Atmosphere

Atmosphere, Vol. 3, Pages 132-163: The Impact of Uncertainties in African Biomass Burning Emission Estimates on Modeling Global Air Quality, Long Range Transport and Tropospheric Chemical Lifetimes

Jason E. Williams — Thu, 09 Feb 2012 00:00:00 CET

The chemical composition of the troposphere in the tropics and Southern Hemisphere (SH) is significantly influenced by gaseous emissions released from African biomass burning (BB). Here we investigate how various emission estimates given in bottom-up BB inventories (GFEDv2, GFEDv3, AMMABB) affect simulations of global tropospheric composition using the TM4 chemistry transport model. The application of various model parameterizations for introducing such emissions is also investigated. There are perturbations in near-surface ozone (O3) and carbon monoxide (CO) of ~60–90% in the tropics and ~5–10% in the SH between different inventories. Increasing the update frequency of the temporal distribution to eight days generally results in decreases of between ~5 and 10% in near-surface mixing ratios throughout the tropics, which is larger than the influence of increasing the injection heights at which BB emissions are introduced. There are also associated differences in the long range transport of pollutants throughout the SH, where the composition of the free troposphere in the SH is sensitive to the chosen BB inventory. Analysis of the chemical budget terms reveals that the influence of increasing the tropospheric CO burden due to BB on oxidative capacity of the troposphere is mitigated by the associated increase in NOx emissions (and thus O3) with the variations in the CO/N ratio between inventories being low. For all inventories there is a decrease in the tropospheric chemical lifetime of methane of between 0.4 and 0.8% regardless of the CO emitted from African BB. This has implications for assessing the effect of inter-annual variability in BB on the annual growth rate of methane.

Atmosphere, Vol. 3, Pages 124-131: Trends in Intense Typhoon Minimum Sea Level Pressure

Stephen L. Durden — Tue, 31 Jan 2012 00:00:00 CET

A number of recent publications have examined trends in the maximum wind speed of tropical cyclones in various basins. In this communication, the author focuses on typhoons in the western North Pacific. Rather than maximum wind speed, the intensity of the storms is measured by their lifetime minimum sea level pressure (MSLP). Quantile regression is used to test for trends in storms of extreme intensity. The results indicate that there is a trend of decreasing intensity in the most intense storms as measured by MSLP over the period 1951–2010. However, when the data are broken into intervals 1951–1987 and 1987–2010, neither interval has a significant trend, but the intensity quantiles for the two periods differ. Reasons for this are discussed, including the cessation of aircraft reconnaissance in 1987. The author also finds that the average typhoon intensity is greater in El Nino years, while the intensity of the strongest typhoons shows no significant relation to El Nino Southern Oscillation.

Atmosphere, Vol. 3, Pages 103-123: An Evaluation of Modeled Plume Injection Height with Satellite-Derived Observed Plume Height

Sean M. Raffuse — Wed, 18 Jan 2012 00:00:00 CET

Plume injection height influences plume transport characteristics, such as range and potential for dilution. We evaluated plume injection height from a predictive wildland fire smoke transport model over the contiguous United States (U.S.) from 2006 to 2008 using satellite-derived information, including plume top heights from the Multi-angle Imaging SpectroRadiometer (MISR) Plume Height Climatology Project and aerosol vertical profiles from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP). While significant geographic variability was found in the comparison between modeled plumes and satellite-detected plumes, modeled plume heights were lower overall. In the eastern U.S., satellite-detected and modeled plume heights were similar (median height 671 and 660 m respectively). Both satellite-derived and modeled plume injection heights were higher in the western U.S. (2345 and 1172 m, respectively). Comparisons of modeled plume injection height to satellite-derived plume height at the fire location (R2 = 0.1) were generally worse than comparisons done downwind of the fire (R2 = 0.22). This suggests that the exact injection height is not as important as placement of the plume in the correct transport layer for transport modeling.

Atmosphere, Vol. 3, Pages 87-102: Atmosphere: A Source of Pathogenic or Beneficial Microbes?

Paraskevi N. Polymenakou — Mon, 16 Jan 2012 00:00:00 CET

The atmosphere has been described as one of the last frontiers of biological exploration on Earth. The composition of microbial communities in the atmosphere is still not well-defined, and taxonomic studies of bacterial diversity in the outdoor air have just started to emerge, whereas our knowledge about the functional potential of air microbiota is scant. When in the air, microorganisms can be attached to ambient particles and/or incorporated into water droplets of clouds, fog, and precipitation (i.e., rain, snow, hail). Further, they can be deposited back to earth’s surfaces via dry and wet deposition processes and they can possibly induce an effect on the diversity and function of aquatic and terrestrial ecosystems or impose impacts to human health through microbial pathogens dispersion. In addition to their impact on ecosystem and public health, there are strong indications that air microbes are metabolically active and well adapted to the harsh atmospheric conditions. Furthermore they can affect atmospheric chemistry and physics, with important implications in meteorology and global climate. This review summarizes current knowledge about the ubiquitous presence of microbes in the atmosphere and discusses their ability to survive in the atmospheric environment. The purpose is to evaluate the atmospheric environment as a source of pathogenic or beneficial microbes and to assess the biotechnological opportunities that may offer.

Atmosphere, Vol. 3, Pages 59-86: An Investigation of Two Highest Ozone Episodes During the Last Decade in New England

Tzu-Ling Lai — Tue, 27 Dec 2011 00:00:00 CET

This study examined the role of meteorological processes in two of the highest ozone (O3) episodes within the last decade at monitoring sites in southern New Hampshire (NH), USA. The highest O3 levels occurred on 14 August 2002 at Thompson Farm (TF) and 22 July 2004 at Castle Springs (CS). Ozone mixing ratios in the 2002 episode showed continual high values (>100 ppbv) at the beginning of the episode, and reached 151 ppbv on 14 August. The 2004 episode consisted of one day of high O3 (>100 ppbv) on 22 July at CS with the peak level of 111 ppbv. Our analysis suggested that the August 2002 high O3 event at TF occurred under stagnant synoptic high-pressure conditions that prevailed over the entire eastern USA for an unusually extended time period. The clear skies and stable meteorological conditions resulted in accumulation of pollutants in the boundary layer. At the same time, the mesoscale low-level-jet (LLJ) played an important role in transporting air masses from the polluted Mid-Atlantic areas to the Northeast. Local land-sea-breeze circulations also added to the impact of this event. Our examination showed that the unprecedented high levels of O3 on 22 July 2004 at CS was driven by two mechanisms, stratospheric intrusion and the Appalachian lee trough (APLT), which was not found during other O3 episodes at the site in the decade long data record. This study demonstrated that unusually high O3 levels at New England rural sites were driven by multi-scale processes, and the regional/local scale processes controlled the magnitude and timing of the local pollution episodes.

Atmosphere, Vol. 3, Pages 33-58: Radar-Based Analysis of Convective Storms over Northwestern Italy

Paolo Davini — Tue, 27 Dec 2011 00:00:00 CET

Thunderstorms may cause large damages to infrastructures and population, therefore the possible identification of the areas with the highest occurrence of these events is especially relevant. Nevertheless, few extensive studies of these phenomena with high spatial and temporal resolution have been carried out in the Alps and none of them includes North-western Italy. To analyze thunderstorm events, the data of the meteorological radar network of the regional meteorological service of Piedmont region (ARPA Piemonte) have been used in this work. The database analyzed includes all thunderstorms occurred during the warm months (April to September) of a 6-year period (2005–2010). The tracks of each storm have been evaluated using a storm tracking algorithm. Several characteristics of the storms have been analyzed, such as the duration, the spatial and the temporaldistribution, the direction and the distance travelled. Obtained results revealed several important characteristics that may be useful for nowcasting purposes providing a first attempt of radar-based climatology in the considered region.

Atmosphere, Vol. 3, Pages 1-32: A Review of Tropospheric Atmospheric Chemistry and Gas-Phase Chemical Mechanisms for Air Quality Modeling

William R. Stockwell — Wed, 21 Dec 2011 00:00:00 CET

Gas-phase chemical mechanisms are vital components of prognostic air quality models. The mechanisms are incorporated into modules that are used to calculate the chemical sources and sinks of ozone and the precursors of particulates. Fifty years ago essential atmospheric chemical processes, such as the importance of the hydroxyl radical, were unknown and crude air quality models incorporated only a few parameterized reactions obtained by fitting observations. Over the years, chemical mechanisms for air quality modeling improved and became more detailed as more experimental data and more powerful computers became available. However it will not be possible to incorporate a detailed treatment of the chemistry for all known chemical constituents because there are thousands of organic compounds emitted into the atmosphere. Some simplified method of treating atmospheric organic chemistry is required to make air quality modeling computationally possible. The majority of the significant differences between air quality mechanisms are due to the differing methods of treating this organic chemistry. The purpose of this review is to present an overview of atmospheric chemistry that is incorporated into air quality mechanisms and to suggest areas in which more research is needed.

Atmosphere, Vol. 2, Pages 715-741: Case Study of Pollutants Concentration Sensitivity to Meteorological Fields and Land Use Parameters over Douala (Cameroon) Using AERMOD Dispersion Model

Pascal Moudi Igri — Wed, 14 Dec 2011 00:00:00 CET

This paper deals with the simulation of the NOx concentration over Douala for the period 2002–2006 by means of the American Meteorological Society (AMS)/Environmental Protection Agency (EPA) Regulatory Model (AERMOD) model, version 07026. Its sensitivity to local meteorological fields and land use parameters are investigated by selecting different buildings (receptors) specific direction and distance from the source and by making changes in land use parameters. Results reveal variations in concentration patterns depending on the roughness length, albedo and the Bowen ratio. Changes in the albedo as well as the Bowen ratio only alter the concentration patterns during convective conditions. For a short averaging time, changes in albedo and Bowen ratio have the same effects on the concentration patterns. These results not only help to accurately choose the indicated areas for implanting industrial sites, to manage risk assessment exposure to pollutants in Douala city and addressing recommendations to policies makers.

Atmosphere, Vol. 2, Pages 702-714: Carbon Dioxide and Methane at a Desert Site—A Case Study at Railroad Valley Playa, Nevada, USA

Emma L. Yates — Thu, 08 Dec 2011 00:00:00 CET

Ground based in-situ measurements of carbon dioxide (CO2) and methane (CH4) at the dry lakebed at Railroad Valley (RRV) playa, Nevada, USA (38°30.234′ N, 115°41.604′ W, elevation 1437 m) were conducted over a five day period from 20–25 June 2010. The playa is a flat, desert site with virtually no vegetation, an overall size of 15 km × 15 km and is approximately 110 km south-west of the nearest city, Ely (elevation 1962 m, inhabitants 4000). The measurements were taken in support of the vicarious calibration experiment to validate column-averaged dry air mole fractions of CO2 and CH4 (XCO2 and XCH4) retrieved from the Greenhouse Gases Observing Satellite (GOSAT) which was launched in January 2009. This work reports on ground-based in-situ measurements of CO2 and CH4 from RRV playa and describes comparisons made between in-situ data and XCO2 and XCH4 from GOSAT.

Atmosphere, Vol. 2, Pages 688-701: A Comparison of Risk Estimates for the Effect of Short-Term Exposure to PM, NO2 and CO on Cardiovascular Hospitalizations and Emergency Department Visits: Effect Size Modeling of Study Findings

Ellen Kirrane — Tue, 06 Dec 2011 00:00:00 CET

Although particulate matter (PM), nitrogen dioxide (NO2) and carbon monoxide (CO) typically exist as part of a complex air pollution mixture, the evidence linking these pollutants to health effects is evaluated separately in the scientific and policy reviews of the National Ambient Air Quality Standards (NAAQS). The objective of this analysis was to use meta-regression methods to model effect estimates for several individual yet correlated NAAQS pollutants in an effort to identify factors that explain differences in the effect sizes across studies and across pollutants. We expected that our consideration of the evidence for several correlated pollutants in parallel could lead to insights regarding exposure to the pollutant mixture. We focused on studies of hospital admissions for congestive heart failure (CHF) and ischemic heart disease (IHD), which have played an important role in the evaluation of the scientific evidence communicated in the PM, NO2, and CO Integrated Science Assessments (ISAs). Of the studies evaluated, 11 CHF studies and 21 IHD studies met our inclusion requirements. The size of the risk estimates was explained by factors related to the pollution mixture, study methods, and monitoring network characteristics. Our findings suggest that additional analyses focusing on understanding differences in effect sizes across geographic areas with different pollution mixtures and monitor network designs may improve our understanding of the independent and combined effects of correlated pollutants.

Atmosphere, Vol. 2, Pages 671-687: Desorption of Herbicides from Atmospheric Particulates During High-Volume Air Sampling

Allan J. Cessna — Mon, 14 Nov 2011 00:00:00 CET

Pesticides can be present in the atmosphere either as vapours and/or in association with suspended particles. High-volume air sampling, in which air is aspirated first through a glass fibre filter to capture pesticides associated with atmospheric particulates and then polyurethane foam (PUF), often in combination with an adsorbent resin such as XAD-2, to capture pesticides present as vapours, is generally employed during atmospheric monitoring for pesticides. However, the particulate fraction may be underestimated because some pesticides may be stripped or desorbed from captured particulates due to the pressure drop created by the high flow of air through the filter. This possibility was investigated with ten herbicide active ingredients commonly used on the Canadian prairies (dimethylamine salts of 2,4-D, MCPA and dicamba, 2,4-D 2-ethylhexyl ester, bromoxynil octanoate, diclofop methyl ester, fenoxaprop ethyl ester, trifluralin, triallate and ethalfluralin) and seven hydrolysis products (2,4-D, MCPA, dicamba, bromoxynil, diclofop, clopyralid and mecoprop). Finely ground heavy clay soil fortified with active ingredients/hydrolysis products was evenly distributed on the glass fibre filters of high-volume air samplers and air aspirated through the samplers at a flow rate of 12.5 m3/h for a 7-day period. The proportion desorbed as vapour from the fortified soil was determined by analysis of the PUF/XAD-2 resin composite cartridges. The extent of desorption from the fortified soil applied to the filters varied from 0% for each of the dimethylamine salts of 2,4-D, MCPA and dicamba to approximately 50% for trifluralin, triallate and ethalfluralin.

Atmosphere, Vol. 2, Pages 655-670: Influence of Reduced Nitrogen Diets on Ammonia Emissions from Cattle Feedlot Pens

Karen Galles — Fri, 11 Nov 2011 00:00:00 CET

Reducing crude protein (CP) in livestock diets may lower ammonia emissions. A feeding trial was conducted with crossbred steers at the Southeast Colorado Research Center in Lamar, Colorado from December 2009 to March 2010. Three diet treatments were investigated: Reduced (11.6% CP), Oscillating (13.5% crude protein 4 days/week and 11.6% CP 3 days/week) and Control (13.5% CP). Intact soil core samples (n = 36 per sampling date) were collected from the pen surfaces on three dates corresponding to 45, 92, and 148 days into the feeding cycle. Four pens from each diet treatment were sampled. Cores were placed into flow-through laboratory chambers for seven days and ammonia fluxes were trapped in acid bubblers that were refreshed every 24 h. Average daily ammonia emissions for the Control diet ranged from 6.6 to 9.4 g NH3 m−2·day−1; average daily emission for the Oscillating diet ranged from 6.3 to 8.8 g NH3 m−2·day−1; and average daily flux for the Reduced diet ranged from 4.1 to 5.8 g NH3 m−2·day−1. Ammonia fluxes from the reduced N treatment were significantly lower (21% to 40%) than from the control diet on the first two sample dates. There was no significant difference between the Oscillating and Control treatments. Reducing CP in cattle feedlot diets may be an effective method for reducing ammonia emissions from pen surfaces. More research is needed to validate these results at commercial scales in different environments to determine if reductions in ammonia can be sustained with lower CP diets without affecting rate of gain, feed efficiency and health.

Atmosphere, Vol. 2, Pages 633-654: Emission Ratios for Ammonia and Formic Acid and Observations of Peroxy Acetyl Nitrate (PAN) and Ethylene in Biomass Burning Smoke as Seen by the Tropospheric Emission Spectrometer (TES)

Matthew J. Alvarado — Wed, 09 Nov 2011 00:00:00 CET

We use the Tropospheric Emission Spectrometer (TES) aboard the NASA Aura satellite to determine the concentrations of the trace gases ammonia (NH3) and formic acid (HCOOH) within boreal biomass burning plumes, and present the first detection of peroxy acetyl nitrate (PAN) and ethylene (C2H4) by TES. We focus on two fresh Canadian plumes observed by TES in the summer of 2008 as part of the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS-B) campaign. We use TES retrievals of NH3 and HCOOH within the smoke plumes to calculate their emission ratios (1.0% ± 0.5% and 0.31% ± 0.21%, respectively) relative to CO for these Canadian fires. The TES derived emission ratios for these gases agree well with previous aircraft and satellite estimates, and can complement ground-based studies that have greater surface sensitivity. We find that TES observes PAN mixing ratios of ~2 ppb within these mid-tropospheric boreal biomass burning plumes when the average cloud optical depth is low ( < 0.1) and that TES can detect C2H4 mixing ratios of ~2 ppb in fresh biomass burning smoke plumes.

Atmosphere, Vol. 2, Pages 617-632: Emission Ratios of the Tropospheric Ozone Precursors Nitrogen Dioxide and Formaldehyde from Australia’s Black Saturday Fires

Emma Young — Mon, 31 Oct 2011 00:00:00 CET

The ‘Black Saturday’ fires were a series of devastating forest fires that burned across Victoria, Australia, during February and March of 2009. In this study we have used satellite data made publically available by NASA from the Ozone Monitoring Instrument (OMI) and the Atmospheric InfraRed Sounder (AIRS) to track the smoke plume from the Black Saturday firestorm and explore the chemical aging of the smoke plume in the first days after emission. We also determined emission ratios for formaldehyde and nitrogen dioxide within smoke from fires actively burning across Victoria between 7 and 17 February 2009. The mean emission ratios with respect to carbon monoxide derived for these two tropospheric ozone precursors are (0.016 ± 0.004 mol.mol−1) for formaldehyde and (0.005 ± 0.002 mol.mol−1) for nitrogen dioxide. The mean emission ratio for formaldehyde with respect to CO is in broad agreement with values previously quoted in the literature for temperate forest fires. However, to our knowledge there are no previous measurements of emission ratios for nitrogen dioxide from Australian temperate forest fires.

Atmosphere, Vol. 2, Pages 567-616: Cloud Processing of Gases and Aerosols in Air Quality Modeling

Wanmin Gong — Mon, 10 Oct 2011 00:00:00 CEST

The representations of cloud processing of gases and aerosols in some of the current state-of-the-art regional air quality models in North America and Europe are reviewed. Key processes reviewed include aerosol activation (or nucleation scavenging of aerosols), aqueous-phase chemistry, and wet deposition/removal of atmospheric tracers. It was found that models vary considerably in the parameterizations or algorithms used in representing these processes. As an emerging area of research, the current understanding of the uptake of water soluble organics by cloud droplets and the potential aqueous-phase reaction pathways leading to the atmospheric secondary organic aerosol (SOA) formation is also reviewed. Sensitivity tests using the AURAMS model have been conducted in order to assess the impact on modeled regional particulate matter (PM) from: (1) the different aerosol activation schemes, (2) the different below-cloud particle scavenging algorithms, and (3) the inclusion of cloud processing of water soluble organics as a potential pathway for the formation of atmospheric SOA. It was found that the modeled droplet number concentrations and ambient PM size distributions were strongly affected by the use of different aerosol activation schemes. The impact on the modeled average ambient PM mass concentration was found to be limited in terms of averaged PM2.5 concentration (~a few percents) but more significant in terms of PM1.0 (up to 10 percents). The modeled ambient PM was found to be moderately sensitive to the below-cloud particle scavenging algorithms, with relative differences up to 10% and 20% in terms of PM2.5 and PM10, respectively, when using the two different algorithms for the scavenging coefficient (Λ) corresponding to the lower and upper bounds in the parameterization for Λ. The model simulation with the additional cloud uptake and processing of water-soluble organic gases was shown to improve the evaluation statistics for modeled PM2.5 OA compared to the IMPROVE network data, and it was demonstrated that the cloud processing of water-soluble organics can indeed be an important mechanism in addition to the traditional secondary organic gas uptake to the particle organic phase.

Atmosphere, Vol. 2, Pages 553-566: Measuring Trace Gas Emission from Multi-Distributed Sources Using Vertical Radial Plume Mapping (VRPM) and Backward Lagrangian Stochastic (bLS) Techniques

Kyoung S. Ro — Fri, 23 Sep 2011 00:00:00 CEST

Two micrometeorological techniques for measuring trace gas emission rates from distributed area sources were evaluated using a variety of synthetic area sources. The vertical radial plume mapping (VRPM) and the backward Lagrangian stochastic (bLS) techniques with an open-path optical spectroscopic sensor were evaluated for relative accuracy for multiple emission-source and sensor configurations. The relative accuracy was calculated by dividing the measured emission rate by the actual emission rate; thus, a relative accuracy of 1.0 represents a perfect measure. For a single area emission source, the VRPM technique yielded a somewhat high relative accuracy of 1.38 ± 0.28. The bLS technique resulted in a relative accuracy close to unity, 0.98 ± 0.24. Relative accuracies for dual source emissions for the VRPM and bLS techniques were somewhat similar to single source emissions, 1.23 ± 0.17 and 0.94 ± 0.24, respectively. When the bLS technique was used with vertical point concentrations, the relative accuracy was unacceptably low,

Atmosphere, Vol. 2, Pages 533-552: Seasonal Gradient Patterns of Polycyclic Aromatic Hydrocarbons and Particulate Matter Concentrations near a Highway

Kyung Hwa Jung — Wed, 21 Sep 2011 00:00:00 CEST

Close proximity to roadways has been associated with higher exposure to traffic-related air pollutants. However, analyses of the effects of season and meteorological parameters on horizontal gradient patterns of traffic-generated air pollutants still need to be elucidated. Our objectives were to: (1) determine effects of season on horizontal gradient patterns of polycyclic aromatic hydrocarbons (PAHs), total suspended particles (TSP), and PM2.5 near a heavily trafficked highway; and (2) examine the effect of day-of-the-week variations (weekday versus weekend) associated with traffic counts on measured airborne-contaminant levels. PAHs (Σ8PAHs [MW 228–278]; gas + particulate), TSP and PM2.5 were monitored at nominal distances (50, 100, and 150 m) from the New Jersey Turnpike every 6 days for periods of 24 h, between September 2007 and September 2008. Seasonal variations in the horizontal gradient patterns of Σ8PAHs were observed. In the summer, Σ8PAHs declined significantly between 50–100 m from the highway (23% decrease), but not between the furthermost distances (100–150 m). An inverse pattern was observed in the winter: Σ8PAHs declined between 100–150 m (26% decrease), but not between the closest distances. Σ8PAHs and TSP, but not PM2.5, concentrations measured on weekends were 12–37% lower than those on weekdays, respectively, corresponding to lower diesel traffic volume. This study suggests that people living in the close proximity to highways may be exposed to varying levels of Σ8PAHs, TSP, and PM2.5 depending on distance to highway, season, and day-of-the-week variations.

Atmosphere, Vol. 2, Pages 510-532: Chemical Mechanism Solvers in Air Quality Models

Hong Zhang — Tue, 13 Sep 2011 00:00:00 CEST

The solution of chemical kinetics is one of the most computationally intensivetasks in atmospheric chemical transport simulations. Due to the stiff nature of the system,implicit time stepping algorithms which repeatedly solve linear systems of equations arenecessary. This paper reviews the issues and challenges associated with the construction ofefficient chemical solvers, discusses several families of algorithms, presents strategies forincreasing computational efficiency, and gives insight into implementing chemical solverson accelerated computer architectures.

Atmosphere, Vol. 2, Pages 484-509: Adaptive Grid Use in Air Quality Modeling

Fernando Garcia-Menendez — Fri, 09 Sep 2011 00:00:00 CEST

The predictions from air quality models are subject to many sources of uncertainty; among them, grid resolution has been viewed as one that is limited by the availability of computational resources. A large grid size can lead to unacceptable errors for many pollutants formed via nonlinear chemical reactions. Further, insufficient grid resolution limits the ability to perform accurate exposure assessments. To address this issue in parallel to increasing computational power, modeling techniques that apply finer grids to areas of interest and coarser grids elsewhere have been developed. Techniques using multiple grid sizes are called nested grid or multiscale modeling techniques. These approaches are limited by uncertainty in the placement of finer grids since pertinent locations may not be known a priori, loss in solution accuracy due to grid boundary interface problems, and inability to adjust to changes in grid resolution requirements. A different approach to achieve local resolution involves using dynamic adaptive grids. Various adaptive mesh refinement techniques using structured grids as well as mesh enrichment techniques on unstructured grids have been explored in atmospheric modeling. Recently, some of these techniques have been applied to full blown air quality models. In this paper, adaptive grid methods used in air quality modeling are reviewed and categorized. The advantages and disadvantages of each adaptive grid method are discussed. Recent advances made in air quality simulation owing to the use of adaptive grids are summarized. Relevant connections to adaptive grid modeling in weather and climate modeling are also described.

Atmosphere, Vol. 2, Pages 464-483: Coupling of Important Physical Processes in the Planetary Boundary Layer between Meteorological and Chemistry Models for Regional to Continental Scale Air Quality Forecasting: An Overview

Pius Lee — Wed, 31 Aug 2011 00:00:00 CEST

A consensus among many Air Quality (AQ) modelers is that planetary boundary layer processes are the most influential processes for surface concentrations of air pollutants. Due to the many uncertainties intrinsically embedded in the parameterization of these processes, parameter optimization is often employed to determine an optimal set or range of values of the sensitive parameters. In this review study, we focus on the two of the most important physical processes: turbulent mixing and dry deposition. An emphasis was put on surveying AQ models that have been proven to resolve meso-scale features and cover a large geographical area, such as large regional, continental, or trans-continental boundary extents. Five AQ models were selected. Four of the models were run in real-time operational forecasting settings for continental scale AQ. The models use various forms of level 2.5 closure algorithms to calculate turbulent mixing. Tuning and parameter optimization has been used to tailor these algorithms to better suit their AQ models which are typically comprised of a coupled chemistry and meteorology model. Longer forecasts and long lead-times are inevitably under increasing demand for these models. Land Surface Models that have the capability for soil moisture and temperature data assimilation will have an advantage to constrain the key variables that govern the partitioning of surface sensible and latent heat fluxes and thus attain the potential to perform better in longer forecasts than those models that do not have this capability. Dry deposition velocity is a very significant model parameter that governs a major surface exchange activity. An exploratory study has been conducted to see the upper bound of roughness length in the similarity equation for aerodynamic resistance.

Atmosphere, Vol. 2, Pages 426-463: Chemical Data Assimilation—An Overview

Adrian Sandu — Mon, 29 Aug 2011 00:00:00 CEST

Chemical data assimilation is the process by which models use measurements to produce an optimal representation of the chemical composition of the atmosphere. Leveraging advances in algorithms and increases in the available computational power, the integration of numerical predictions and observations has started to play an important role in air quality modeling. This paper gives an overview of several methodologies used in chemical data assimilation. We discuss the Bayesian framework for developing data assimilation systems, the suboptimal and the ensemble Kalman filter approaches, the optimal interpolation (OI), and the three and four dimensional variational methods. Examples of assimilation real observations with CMAQ model are presented.

Atmosphere, Vol. 2, Pages 407-425: Air Quality Response Modeling for Decision Support

Daniel S. Cohan — Fri, 26 Aug 2011 00:00:00 CEST

Air quality management relies on photochemical models to predict the responses of pollutant concentrations to changes in emissions. Such modeling is especially important for secondary pollutants such as ozone and fine particulate matter which vary nonlinearly with changes in emissions. Numerous techniques for probing pollutant-emission relationships within photochemical models have been developed and deployed for a variety of decision support applications. However, atmospheric response modeling remains complicated by the challenge of validating sensitivity results against observable data. This manuscript reviews the state of the science of atmospheric response modeling as well as efforts to characterize the accuracy and uncertainty of sensitivity results.

Atmosphere, Vol. 2, Pages 389-406: Sub-Grid Scale Plume Modeling

Prakash Karamchandani — Wed, 24 Aug 2011 00:00:00 CEST

Multi-pollutant chemical transport models (CTMs) are being routinely used to predict the impacts of emission controls on the concentrations and deposition of primary and secondary pollutants. While these models have a fairly comprehensive treatment of the governing atmospheric processes, they are unable to correctly represent processes that occur at very fine scales, such as the near-source transport and chemistry of emissions from elevated point sources, because of their relatively coarse horizontal resolution. Several different approaches have been used to address this limitation, such as using fine grids, adaptive grids, hybrid modeling, or an embedded sub-grid scale plume model, i.e., plume-in-grid (PinG) modeling. In this paper, we first discuss the relative merits of these various approaches used to resolve sub-grid scale effects in grid models, and then focus on PinG modeling which has been very effective in addressing the problems listed above. We start with a history and review of PinG modeling from its initial applications for ozone modeling in the Urban Airshed Model (UAM) in the early 1980s using a relatively simple plume model, to more sophisticated and state-of-the-science plume models, that include a full treatment of gas-phase, aerosol, and cloud chemistry, embedded in contemporary models such as CMAQ, CAMx, and WRF-Chem. We present examples of some typical results from PinG modeling for a variety of applications, discuss the implications of PinG on model predictions of source attribution, and discuss possible future developments and applications for PinG modeling.

Atmosphere, Vol. 2, Pages 358-388: Modeling Smoke Plume-Rise and Dispersion from Southern United States Prescribed Burns with Daysmoke

Gary L. Achtemeier — Fri, 19 Aug 2011 00:00:00 CEST

We present Daysmoke, an empirical-statistical plume rise and dispersion model for simulating smoke from prescribed burns. Prescribed fires are characterized by complex plume structure including multiple-core updrafts which makes modeling with simple plume models difficult. Daysmoke accounts for plume structure in a three-dimensional veering/sheering atmospheric environment, multiple-core updrafts, and detrainment of particulate matter. The number of empirical coefficients appearing in the model theory is reduced through a sensitivity analysis with the Fourier Amplitude Sensitivity Test (FAST). Daysmoke simulations for “bent-over” plumes compare closely with Briggs theory although the two-thirds law is not explicit in Daysmoke. However, the solutions for the “highly-tilted” plume characterized by weak buoyancy, low initial vertical velocity, and large initial plume diameter depart considerably from Briggs theory. Results from a study of weak plumes from prescribed burns at Fort Benning GA showed simulated ground-level PM2.5 comparing favorably with observations taken within the first eight kilometers of eleven prescribed burns. Daysmoke placed plume tops near the lower end of the range of observed plume tops for six prescribed burns. Daysmoke provides the levels and amounts of smoke injected into regional scale air quality models. Results from CMAQ with and without an adaptive grid are presented.

Atmosphere, Vol. 2, Pages 330-357: Climate Variability and Its Impact on Forest Hydrology on South Carolina Coastal Plain, USA

Zhaohua Dai — Tue, 16 Aug 2011 00:00:00 CEST

Understanding the changes in hydrology of coastal forested wetlands induced by climate change is fundamental for developing strategies to sustain their functions and services. This study examined 60 years of climatic observations and 30 years of hydrological data, collected at the Santee Experimental Forest (SEF) in coastal South Carolina. We also applied a physically-based, distributed hydrological model (MIKE SHE) to better understand the hydrological responses to the observed climate variability. The results from both observation and simulation for the paired forested watershed systems indicated that the forest hydrology was highly susceptible to change due to climate change. The stream flow and water table depth was substantially altered with a change in precipitation. Both flow and water table level decreased with a rise in temperature. The results also showed that hurricanes substantially influenced the forest hydrological patterns for a short time period (several years) as a result of forest damage.

Atmosphere, Vol. 2, Pages 303-329: Greenhouse Gas Emissions from Ground Level Area Sources in Dairy and Cattle Feedyard Operations

Md Saidul Borhan — Tue, 09 Aug 2011 00:00:00 CEST

A protocol that consisted of an isolation flux chamber and a portable gas chromatograph was used to directly quantify greenhouse gas (GHG) emissions at a dairy and a feedyard operation in the Texas Panhandle. Field sampling campaigns were performed 5 consecutive days only during daylight hours from 9:00 am to 7:00 pm each day. The objective of this research was to quantify and compare GHG emission rates (ERs) from ground level area sources (GLAS) at dairy and cattle feedyard operations during the summer. A total of 74 air samples using flux chamber were collected from the barn (manure lane and bedding area), loafing pen, open lot, settling basin, lagoons, and compost pile within the dairy operation. For the cattle feedyard, a total of 87 air samples were collected from four corner pens of a large feedlot, runoff holding pond, and compost pile. Three primary GHGs (methane, carbon dioxide, and nitrous oxide) were measured and quantified from both operations. The aggregate estimated ERs for CH4, CO2, and N2O were 836, 5573, 3.4 g hd−1 d−1 (collectively 27.5 kg carbon dioxide equivalent (CO2e) hd−1 d−1), respectively, at the dairy operation. The aggregate ERs for CH4, CO2, and N2O were 3.8, 1399, 0.68 g hd−1 d−1 (1.7 kg CO2e hd−1 d−1), respectively, from the feedyard. The estimated USEPA GHG ERs were about 13.2 and 1.16 kg CO2e hd−1 d−1, respectively, for dairy and feedyard operations. Aggregate CH4, CO2 and N2O ERs at the dairy facility were about 219, 4 and 5 times higher, respectively, than those at the feedyard. At the dairy, average CH4 ERs estimated from the settling basin, primary and secondary lagoons were significantly higher than those from the other GLAS, contributing about 98% of the aggregate CH4 emission. The runoff holding pond and pen surface of the feedyard contributed about 99% of the aggregate CH4 emission. Average CO2 and N2O ERs estimated from the pen surface area were significantly higher than those estimated from the compost pile and runoff pond. The pen surface alone contributed about 93% and 84% of the aggregate CO2 and N2O emission, respectively. Abatement and management practices that address GHG emissions from these sources will likely be most effective for reducing facility emissions.

Atmosphere, Vol. 2, Pages 271-302: Surface Flux Modeling for Air Quality Applications

Jonathan Pleim — Mon, 08 Aug 2011 00:00:00 CEST

For many gasses and aerosols, dry deposition is an important sink of atmospheric mass. Dry deposition fluxes are also important sources of pollutants to terrestrial and aquatic ecosystems. The surface fluxes of some gases, such as ammonia, mercury, and certain volatile organic compounds, can be upward into the air as well as downward to the surface and therefore should be modeled as bi-directional fluxes. Model parameterizations of dry deposition in air quality models have been represented by simple electrical resistance analogs for almost 30 years. Uncertainties in surface flux modeling in global to mesoscale models are being slowly reduced as more field measurements provide constraints on parameterizations. However, at the same time, more chemical species are being added to surface flux models as air quality models are expanded to include more complex chemistry and are being applied to a wider array of environmental issues. Since surface flux measurements of many of these chemicals are still lacking, resistances are usually parameterized using simple scaling by water or lipid solubility and reactivity. Advances in recent years have included bi-directional flux algorithms that require a shift from pre-computation of deposition velocities to fully integrated surface flux calculations within air quality models. Improved modeling of the stomatal component of chemical surface fluxes has resulted from improved evapotranspiration modeling in land surface models and closer integration between meteorology and air quality models. Satellite-derived land use characterization and vegetation products and indices are improving model representation of spatial and temporal variations in surface flux processes. This review describes the current state of chemical dry deposition modeling, recent progress in bi-directional flux modeling, synergistic model development research with field measurements, and coupling with meteorological land surface models.

Atmosphere, Vol. 2, Pages 256-270: Nitrogen Isotope Fractionation and Origin of Ammonia Nitrogen Volatilized from Cattle Manure in Simulated Storage

Chanhee Lee — Tue, 02 Aug 2011 00:00:00 CEST

A series of laboratory experiments were conducted to establish the relationship between nitrogen (N) isotope composition of cattle manure and ammonia emissions, potential contribution of nitrogenous gases other than ammonia to manure N volatilization losses, and to determine the relative contribution of urinary- vs. fecal-N to ammonia emissions during the initial stage of manure storage. Data confirmed that ammonia volatilization losses from manure are most intensive during the first 2 to 3 days of storage and this coincides with a very rapid loss (hydrolysis) of urinary urea. Long-term (30 days) monitoring of δ15N of manure and emitted ammonia indicated that the dynamics of N isotope fractionation may be complicating the usefulness of the isotope approach as a tool for estimating ammonia emissions from manure in field conditions. The relationship between δ15N of manure and ammonia emission appears to be linear during the initial stages of manure storage (when most of the ammonia losses occur) and should be further investigated. These experiments demonstrated that the main source of ammonia-N volatilized from cattle manure during the initial 10 days of storage is urinary-N, representing on average 90% of the emitted ammonia-N. The contribution of fecal-N was relatively low, but gradually increased to about 10% by day 10. There appears to be substantial emissions of nitrogenous gases other than ammonia, most likely dinitrogen gas, which may account for up to 25% of N losses during the first 20 days of manure storage. This finding, which has to be confirmed in laboratory and field conditions, may be indicative of overestimation of ammonia emissions from cattle operations by the current emissions factors.

Atmosphere, Vol. 2, Pages 242-255: Cross-Comparison of MODIS and CloudSat Data as a Tool to Validate Local Cloud Cover Masks

Claudia Notarnicola — Fri, 22 Jul 2011 00:00:00 CEST

This paper presents a cross-comparison of the data acquired by the MODIS and CloudSat sensors in order to understand the limit of the developed cloud-mask algorithm and to provide a quantitative validation assessment of cloud masks by using exclusively remotely sensed data. The analysis has been carried out by comparing both the intermediate levels of the cloud mask such as the brightness temperatures and the reflectance values for different channels, and the cloud mask itself with the cloud profiles as measured by the CloudSat sensor. The comparison between MODIS cloud tests and the CloudSat profiles indicates an agreement with hit rates (H) and Hanssen-Kuiper Skill Score (KSS) varying between 0.7 and 1.0 and 0.4 and 1.0, respectively. In this case, the low values of H and KSS are found due to the limitation of CloudSat to detect low clouds. The comparison between the cloud mask and the CloudSat profile determines H and KSS values between 0.6 and 1, except for one case. The CloudSat profile has also been compared with the Standard MODIS cloud mask in order to understand the improvement obtained in the use of local adapted thresholds. A comparison of MODIS and CALIPSO data is also presented.

Atmosphere, Vol. 2, Pages 222-241: The Coupled Effect of Mid-Tropospheric Moisture and Aerosol Abundance on Deep Convective Cloud Dynamics and Microphysics

Zhiqiang Cui — Tue, 19 Jul 2011 00:00:00 CEST

The humidity of the mid troposphere has a significant effect on the development of deep convection. Dry layers (dry intrusions) can inhibit deep convection through the effect of a thermal inversion resulting from radiation and due to the reduction in buoyancy resulting from entrainment. Recent observations have shown that the sensitivity of cloud top height to changes in mid-tropospheric humidity can be larger than straightforward “parcel dilution” would lead us to expect. Here, we investigate how aerosol effects on cloud development and microphysics are coupled to the effects of mid-tropospheric dry air. The two effects are coupled because the buoyancy loss through entrainment depends on droplet evaporation, so is controlled both by the environmental humidity and by droplet sizes, which are, in turn, controlled in part by the aerosol size distribution. Previous studies have not taken these microphysical effects into account. Cloud development and microphysics are examined using a 2-D non-hydrostatic cloud model with a detailed treatment of aerosol, drop, and ice-phase hydrometeor size spectra. A moderately deep mixed-phase convective cloud that developed over the High Plains of the United States is simulated. We find that a dry layer in the mid troposphere leads to a reduction in cloud updraft strength, droplet number, liquid water content and ice mass above the layer. The effect of the dry layer on these cloud properties is greatly enhanced under elevated aerosol conditions. In an environment with doubled aerosol number (but still realistic for continental conditions) the dry layer has about a three-times larger effect on cloud drop number and 50% greater effect on ice mass compared to an environment with lower aerosol. In the case with high aerosol loading, the dry layer stops convective development for over 10 min, and the maximum cloud top height reached is lower. However, the effect of the dry layer on cloud vertical development is significantly reduced when aerosol concentrations are lower. The coupled effect of mid-tropospheric dry air and aerosol on convective development is an additional way in which long term changes in aerosol may impact planetary cloud processes and climate.

Atmosphere, Vol. 2, Pages 201-221: Influence of Climatic Changes on Pollution Levels in Hungary and Surrounding Countries

Zahari Zlatev — Mon, 18 Jul 2011 00:00:00 CEST

The influence of future climatic changes on some high pollution levels that can cause damage to plants and human beings is studied in this paper. The particular area of interest is Hungary and its surrounding countries. Three important quantities, which are closely related to ozone concentrations, have been investigated. We shall mainly focus on cases where the critical values, prescribed in the directives, are exceeded. Six scenarios, which allow us to compare directly the future and the present levels, have been run over a period of sixteen years. Some of the results obtained in the selected domain by using these scenarios have been carefully studied. The major conclusion is that an increase in temperature in combination with some other factors might lead to rather considerable increases of the damaging effects of ozone on plants and humans.

Atmosphere, Vol. 2, Pages 182-200: Emissions from Ethanol-Gasoline Blends: A Single Particle Perspective

Dabrina D. Dutcher — Wed, 22 Jun 2011 00:00:00 CEST

Due to its agricultural origin and function as a fuel oxygenate, ethanol is being promoted as an alternative biomass-based fuel for use in spark ignition engines, with mandates for its use at state and regional levels. While it has been established that the addition of ethanol to a fuel reduces the particulate mass concentration in the exhaust, little attention has been paid to changes in the physicochemical properties of the emitted particles. In this work, a dynamometer-mounted GM Quad-4 spark ignition engine run without aftertreatment at 1,500 RPM and 100% load was used with four different fuel blends, containing 0, 20, 40 and 85 percent ethanol in gasoline. This allowed the effects of the fuel composition to be isolated from other effects. Instrumentation employed included two Aerosol Time-of-Flight Mass Spectrometers covering different size ranges for analysis of single particle composition, an Aethalometer for black carbon, a Scanning Mobility Particle Sizer for particle size distributions, a Photoelectric Aerosol Sensor for particle-bound polycyclic aromatic hydrocarbon (PAH) species and gravimetric filter measurements for particulate mass concentrations. It was found that, under the conditions investigated here, additional ethanol content in the fuel changes the particle size distribution, especially in the accumulation mode, and decreases the black carbon and total particulate mass concentrations. The molecular weight distribution of the PAHs was found to decrease with added ethanol. However, PAHs produced from higher ethanol-content fuels are associated with NO2− (m/z—46) in the single-particle mass spectra, indicating the presence of nitro-PAHs. Compounds associated with the gasoline (e.g., sulfur-containing species) are diminished due to dilution as ethanol is added to the fuel relative to those associated with the lubricating oil (e.g., calcium, zinc, phosphate) in the single particle spectra. These changes have potential implications for the health effect impacts of particulate emissions from biofuel blends.

Atmosphere, Vol. 2, Pages 171-181: No Borders for Tobacco Smoke in Hospitality Venues in Vienna

Herbert Pletz — Fri, 17 Jun 2011 00:00:00 CEST

In public places many countries banned smoking as the most important indoor source of fine airborne particulate matter. In Austria partial bans have been in force since 2009, with exemptions for the hospitality industry. From February to October 2010 we investigated PM2.5 concentrations in the breathing area of guests in well frequented Viennese establishments of all sizes, and compared these chance indoor samples with PM2.5 concentrations measured during the same half hour at the next outdoor monitoring station. The laser particle counter (OPC1.108, Grimm®) used for indoor measurements had been calibrated by ß-attenuation (FH 62 I-R, Eberline®), which was used outdoors. 48% of 112 venues visited did not fully comply with the law, notwithstanding its weakness. Highest median concentrations (in µg/m3) were found in bars (443.7), followed by nightclubs/discotheques (421.1), pubs (147.7), cafes (106.1) and restaurants (23.4). Concentrations increased with number of smokers present (p < 0.01), with medians of 282.4/241,3/67.6/6.9 µg/m³ in smoking venues/smoking rooms/adjacent non-smoking rooms/exclusive non-smoking venues. Only for the latter, a significant correlation was found with outdoor concentrations (r = 0.48, p < 0.01), while concentrations in non-smoking rooms were higher (p < 0.01) and unrelated to outdoor concentrations, but significantly dependent on concentrations in the adjacent smoking room (r = 0.64, p < 0.01). In conclusion, the partial smoking ban failed and guests of Viennese hospitality venues continue to risk disease from passive smoking, even in so-called “non-smoking rooms”, which are second-hand smoke rooms.

Atmosphere, Vol. 2, Pages 146-170: An Ensemble of Arctic Simulations of the AOE-2001 Field Experiment

Per Axelsson — Wed, 25 May 2011 00:00:00 CEST

An ensemble of model runs with the COAMPS© regional model is compared to observations in the central Arctic for August 2001 from the Arctic Ocean Experiment 2001 (AOE-2001). The results are from a 6-km horizontal resolution 2nd, inner, nest of the model while the outermost model domain covers the pan-Arctic region, including the marginal ice zone and some of the land areas around the Arctic Ocean. Sea surface temperature and ice cover were prescribed from satellite data while sea-ice surface properties were modeled with an energy balance model, assuming a constant ice thickness. Five ensemble members were generated by altering the initialization time for the innermost nest, the surface roughness and the turbulent mixing scheme for clouds. The large size of the outer domain means that the model simulations have substantial deviations from the observations at synoptic-scale time scales. Therefore the evaluation focuses on statistical measures, rather than in details of individual ensemble member performance as compared directly to observations. In this context, the ensemble members are surprisingly similar even though details differ significantly. The ensemble average results features two main systematic problems: a consistent temperature bias, with too low temperatures below 2–3 km and slightly high temperatures through the rest of the troposphere, and a significant underestimation of the lowest clouds. In terms of total cloud cover, however, the model produces a realistic result; it is the very lowest clouds that are essentially missing. The temperature bias initially appears to be related to an interaction between clouds and radiation; the shape of the mean radiative heating-rate profile is very similar to that of the temperature bias. The lack of the lowest clouds could be due to the too low temperatures in conjunction with a cloud scheme that overestimates the transfer of cloud droplets to ice particles that precipitate. The different terms in the surface energy balance as well as the surface stress has only small systematic errors and are surprisingly consistent between the members.

Atmosphere, Vol. 2, Pages 129-145: Climate Signals on the Regional Scale Derived with a Statistical Method: Relevance of the Driving Model’s Resolution

Frank Kreienkamp — Mon, 23 May 2011 00:00:00 CEST

When assessing the magnitude of climate signals in a regional scale, a host of optional approaches is feasible. This encompasses the use of regional climate models (RCM), nested into global climate models (GCM) for an area of interest as well as employing empirical statistical downscaling methods (ESD). In this context the question is addressed: Is an empirical statistical downscaling method capable of yielding results that are comparable to those by dynamical RCMs? Based on the presented ESD method, the comparison of RCM and ESD results show a high amount of agreement. In addition the empirical statistical downscaling can be applied directly to a GCM or a GCM-RCM cascade. The paper aims at comparing the consequences of employing various CGM-RCM-ESD combinations on the derived future changes of temperature and precipitation. This adds to the insight on the scale dependency of downscaling strategies. Results for one GCM with several scenario runs driving several RCMs with and without subsequent empirical statistical downscaling are presented. It is shown that there are only small differences between using the GCM results directly or as a GCM-RCM-ESD cascade.

Atmosphere, Vol. 2, Pages 110-128: Improving Ammonia Emission Modeling and Inventories by Data Mining and Intelligent Interpretation of the National Air Emission Monitoring Study Database

Ji-Qin Ni — Mon, 16 May 2011 00:00:00 CEST

Ammonia emission is one of the greatest environmental concerns in sustainable agriculture development. Several limitations and fundamental problems associated with the current agricultural ammonia emission modeling and emission inventories have been identified. They were associated with a significant disconnection between field monitoring data and knowledge about the data. Comprehensive field measurement datasets have not been fully exploited for scientific research and emission regulations. This situation can be considerably improved if the currently available data are better interpreted and the new knowledge is applied to update ammonia emission modeling techniques. The world’s largest agricultural air quality monitoring database with more than 2.4 billion data points has recently been created by the United States’ National Air Emission Monitoring Study. New approaches of data mining and intelligent interpretation of the database are planned to uncover new knowledge and to answer a series of questions that have been raised. The expected results of this new research idea include enhanced fundamental understanding of ammonia emissions from animal agriculture and improved accuracy and scope in regional and national ammonia emission inventories.

Atmosphere, Vol. 2, Pages 96-109: Effects of Floor Level and Building Type on Residential Levels of Outdoor and Indoor Polycyclic Aromatic Hydrocarbons, Black Carbon, and Particulate Matter in New York City

Kyung Hwa Jung — Mon, 16 May 2011 00:00:00 CEST

Consideration of the relationship between residential floor level and concentration of traffic-related airborne pollutants may predict individual residential exposure among inner city dwellers more accurately. Our objective was to characterize the vertical gradient of residential levels of polycyclic aromatic hydrocarbons (PAH; dichotomized into Σ8PAHsemivolatile (MW 178–206), and Σ8PAHnonvolatile (MW 228–278), black carbon (BC), PM2.5 (particulate matter) by floor level (FL), season and building type. We hypothesize that PAH, BC and PM2.5 concentrations may decrease with higher FL and the vertical gradients of these compounds would be affected by heating season and building type. PAH, BC and PM2.5 were measured over a two-week period outdoor and indoor of the residences of a cohort of 5–6 year old children (n = 339) living in New York City’s Northern Manhattan and the Bronx. Airborne-pollutant levels were analyzed by three categorized FL groups (0–2nd, 3rd–5th, and 6th–32nd FL) and two building types (low-rise versus high-rise apartment building). Indoor Σ8PAHnonvolatile and BC levels declined with increasing FL. During the nonheating season, the median outdoor Σ8PAHnonvolatile, but not Σ8PAHsemivolatile, level at 6th–2nd FL was 1.5–2 times lower than levels measured at lower FL. Similarly, outdoor and indoor BC concentrations at 6th–32nd FL were significantly lower than those at lower FL only during the nonheating season (p < 0.05). In addition, living in a low-rise building was associated significantly with higher levels of Σ8PAHnonvolatile and BC. These results suggest that young inner city children may be exposed to varying levels of air pollutants depending on their FL, season, and building type.

Atmosphere, Vol. 2, Pages 67-95: The Importance of Lateral Boundaries, Surface Forcing and Choice of Domain Size for Dynamical Downscaling of Global Climate Simulations

Morten A.Ø. Køltzow — Wed, 11 May 2011 00:00:00 CEST

Dynamical downscaling by atmospheric Regional Climate Models (RCMs) forced with low-resolution data should produce climate details and add quality and value to the low-resolution data. The aim of this study was to explore the importance of (i) the oceanic surface forcing (sea-surface temperature (SST) and sea-ice), (ii) the lateral boundary condition data, and (iii) the size of the integration domain with respect to improved quality and value in dynamically downscaled data. Experiments addressing the three aspects were performed and the results were investigated for mean sea level pressure (mslp), 2 m air temperature (T2m) and daily precipitation. Although changes in SST gave a clear response locally, changes in the lateral boundary data and the size of the integration domain turned out to be more important with our geographical scope being Norway. The T2m turned out less sensitive to the changes in lateral forcing and the size of the integration domain than mslp and precipitation. The sensitivity for all three variables differed between Norwegian regions; northern parts of Norway were the most sensitive. Even though the sensitivities found in this study might be different in other regions and for other RCMs, these results call for careful consideration when choosing integration domain and driving lateral boundary data when performing dynamical downscaling.

Atmosphere, Vol. 2, Pages 57-66: Diurnal Cycle of the North American Monsoon in a Mesoscale Model Simulation: Evolution of Key Parameters in Relation to Precipitation

Bin Guan — Wed, 06 Apr 2011 00:00:00 CEST

The diurnal cycle of the North American monsoon is analyzed based on the output from a mesoscale model simulation. Statistically significant diurnal cycle in precipitation is identified, with heavy precipitation—essentially convective—dominating in local afternoons. Temporal evolution of key parameters in relation to precipitation is investigated, based on which a sequence of the dynamic/thermodynamic processes underlying precipitation development is proposed. Particularly, the afternoon peak in precipitation is found preceded by enhanced static instability and low-level convergence.

Atmosphere, Vol. 2, Pages 36-56: Challenges and Approaches for Developing Ultrafine Particle Emission Inventories for Motor Vehicle and Bus Fleets

Diane U. Keogh — Thu, 24 Mar 2011 00:00:00 CET

Motor vehicles in urban areas are the main source of ultrafine particles (diameters < 0.1 µm). Ultrafine particles are generally measured in terms of particle number because they have little mass and are prolific in terms of their numbers. These sized particles are of particular interest because of their ability to enter deep into the human respiratory system and contribute to negative health effects. Currently ultrafine particles are neither regularly monitored nor regulated by ambient air quality standards. Motor vehicle and bus fleet inventories, epidemiological studies and studies of the chemical composition of ultrafine particles are urgently needed to inform scientific debate and guide development of air quality standards and regulation to control this important pollution source. This article discusses some of the many challenges associated with modelling and quantifying ultrafine particle concentrations and emission rates for developing inventories and microscale modelling of motor vehicles and buses, including the challenge of understanding and quantifying secondary particle formation. Recommendations are made concerning the application of particle emission factors in developing ultrafine particle inventories for motor vehicle fleets. The article presents a précis of the first published inventory of ultrafine particles (particle number) developed for the urban South-East Queensland motor vehicle and bus fleet in Australia, and comments on the applicability of the comprehensive set of average particle emission factors used in this inventory, for developing ultrafine particle (particle number) and particle mass inventories in other developed countries.

Atmosphere, Vol. 2, Pages 21-35: An Analytical Simple Formula for the Ground Level Concentration from a Point Source

Tiziano Tirabassi — Thu, 24 Mar 2011 00:00:00 CET

The Advection-Diffusion Equation is solved for a constant pollutant emission from a point-like source placed inside an unstable Atmospheric Boundary Layer. The solution is obtained adopting the novel analytical approach: Generalized Integral Laplace Transform Technique. The concentration solution of the equation is expressed through an infinite series expansion. After setting a realistic scenario through the wind and diffusivity parameterizations, the Ground Level Concentration (GLC) is determined, and an explicit approximate expression is provided for it, allowing an analytically simple expression for the position and value of the maximum. Remarks arise regarding the ability to express value and position of the GLC as explicit functions of the parameters defining the Atmospheric Boundary Layer scenario and the source height.

Atmosphere, Vol. 2, Pages 1-20: Comparison of Particulate Mercury Measured with Manual and Automated Methods

Robert Talbot — Thu, 20 Jan 2011 00:00:00 CET

A study was conducted to compare measuring particulate mercury (HgP) with the manual filter method and the automated Tekran system. Simultaneous measurements were conducted with the Tekran and Teflon filter methodologies in the marine and coastal continental atmospheres. Overall, the filter HgP values were on the average 21% higher than the Tekran HgP, and >85% of the data were outside of ±25% region surrounding the 1:1 line. In some cases the filter values were as much as 3-fold greater, with

Atmosphere, Vol. 1, Pages 62-84: The Influence of Stratospheric Sulphate Aerosol Deployment on the Surface Air Temperature and the Risk of an Abrupt Global Warming

Pedro Llanillo — Fri, 10 Dec 2010 00:00:00 CET

We used the ‘Radiative-Convective Model of the Earth-atmosphere system’ (OGIM) to investigate the cooling effects induced by sulphur injections into the stratosphere. The ensemble of numerical calculations was based on the A1B scenario from the IPCC Special Report on Emissions Scenarios (SRES). Several geoengineered scenarios were analysed, including the abrupt interruption of these injections in different scenarios and at different dates. We focused on the surface air temperature (SAT) anomalies induced by stratospheric sulphate aerosol generated in order to compensate future warming. Results show that continuous deployment of sulphur into the stratosphere could induce a lasting decrease in SAT. Retaining a constant aerosol loading equivalent to 6 TgS would delay the expected global warming by 53 years. Keeping the SAT constant in a context of increasing greenhouse gases (GHGs) means that the aerosol loading needs to be increased by 1.9% annually. This would offset the effect of increasing GHG under the A1B scenario. A major focus of this study was on the heating rates of SAT that would arise in different scenarios in case of an abrupt cessation of sulphur injections into the stratosphere. Our model results show that heating rates after geoengineering interruption would be 15–28 times higher than in a case without geoengineering, with likely important consequences for life on Earth. Larger initial sulphate loadings induced more intense warming rates when the geoengineering was stopped at the same time. This implies that, if sulphate loading was increased to maintain constant SAT in the light of increasing GHG concentrations, the later the geoengineering interruption was to occur, the higher the heating rates would be. Consequently, geoengineering techniques like this should only be regarded as last-resort measures and require intense further research should they ever become necessary.

Atmosphere, Vol. 1, Pages 51-61: Assessment of Maximum Possible Urbanization Influences on Land Temperature Data by Comparison of Land and Marine Data around Coasts

Dimitrios A. Efthymiadis — Mon, 06 Dec 2010 00:00:00 CET

Global surface temperature trends, based on land and marine data, show warming of about 0.8 °C over the last 100 years. This rate of warming is sometimes questioned because of the existence of Urban Heat Islands (UHIs). In this study we compare the rate of temperature change estimated from measurements of land and marine temperatures for the same grid squares using 5° by 5° latitude/longitude grid-box datasets. For 1951–2009 the ‘land’ average warmed by 0.02 °C decade−1 relative to the ‘sea surface temperature’ (SST) average. There were regional contrasts in the trends of land/sea temperature differences: the land warmed at a greater rate compared to the SST for regions north of 20°S, but the opposite occurred further south. Given strong forcing of the climate system, we would expect the land to change more rapidly than the ocean, so the differences represent an upper limit to the urbanization effect.

Atmosphere, Vol. 1, Pages 34-50: Oceanic Dimethyl Sulfide Emission and New Particle Formation around the Coast of Antarctica: A Modeling Study of Seasonal Variations and Comparison with Measurements

Fangqun Yu — Mon, 06 Dec 2010 00:00:00 CET

A clear understanding of new particle formation processes in remote oceans is critical for properly assessing the role of oceanic dimethyl sulfide (DMS) emission on the Earth’s climate and associated climate feedback processes. Almost free from anthropogenic pollutants and leafed plants, the Antarctic continent and surrounding oceans are unique regions for studying the lifecycle of natural sulfate aerosols. Here we investigate the well-recognized seasonal variations of new particle formation around Antarctic coastal areas with a recently developed global size-resolved aerosol model. Our simulations indicate that enhanced DMS emission and photochemistry during the austral summer season lead to significant new particle formation via ion-mediated nucleation (IMN) and much higher particle number concentrations over Antarctica and surrounding oceans. By comparing predicted condensation nuclei larger than 10 nm (CN10) during a three-year period (2005–2007) with the long-period continuous CN10 measurements at the German Antarctic station Neumayer, we show that the model captures the absolute values of monthly mean CN10 (within a factor 2–3) as well as their seasonal variations. Our simulations confirm that the observed Antarctic CN10 and cloud condensation nuclei (CCN) seasonal variations are due to the formation of secondary particles during the austral summer. From the austral winter to summer, the zonally averaged CN10 and CCN in the lower troposphere over Antarctica increase by a factor of ~4–6 and ~2–4, respectively. This study appears to show that the H2SO4-H2O IMN mechanism is able to account for the new particle formation frequently observed in the Antarctica region during the austral summer.

Atmosphere, Vol. 1, Pages 15-33: Remote Sensing and Modeling of Cyclone Monica near Peak Intensity

Stephen L. Durden — Mon, 12 Jul 2010 00:00:00 CEST

Cyclone Monica was an intense Southern Hemisphere tropical cyclone of 2006. Although no in situ measurements of Monica’s inner core were made, microwave, infrared, and visible satellite instruments observed Monica before and during peak intensity through landfall on Australia’s northern coast. The author analyzes remote sensing measurements in detail to investigate Monica’s intensity. While Dvorak analysis of its imagery argues that it was of extreme intensity, infrared and microwave soundings indicate a somewhat lower intensity, especially as it neared landfall. The author also describes several numerical model runs that were made to investigate the maximum possible intensity for the observed environmental conditions; these simulations also suggest a lower intensity than estimates from Dvorak analysis alone. Based on the evidence from the various measurements and modeling, the estimated range for the minimum sea level pressure at peak intensity is 900 to 920 hPa. The estimated range for the one-minute averaged maximum wind speed at peak intensity is 72 to 82 m/s. These maxima were likely reached about 24 hours prior to landfall, with some weakening occurring afterward.

Atmosphere, Vol. 1, Pages 3-14: Correlation of Air Quality Data to Ultrafine Particles (UFP) Concentration and Size Distribution in Ambient Air

Kwasny — Mon, 12 Jul 2010 00:00:00 CEST

This study monitored ultrafine particles (UFP) concurrent with environmental air quality data, investigating whether already existing instrumentation used by environmental authorities can provide reference values for estimating UFP concentrations. Of particular interest was the relation of UFP to PM10 (particulate matter) and nitrogen oxides (NOx, NO2) in ambient air. Existing PM measurement methods alone did not correspond exactly enough with the actual particle number, but we observed a link between NOx and NO2 to UFP concentration. The combined data could act as proxy-indicator for authorities in estimating particle number concentrations, but cannot replace UFP monitoring.

Atmosphere, Vol. 1, Pages 1-2: Atmosphere: An International and Interdisciplinary Scientific Open Access Journal

Jacob — Fri, 09 Jul 2010 00:00:00 CEST

The new online, Open Access journal Atmosphere has been launched to present reviews, regular research papers, communications and short notes on atmospheric topics. These topics include experimental and theoretical work related to the physical atmosphere, such as turbulence, atmospheric flow, dynamic and physical processes and mechanisms, atmospheric chemistry, such as changes in atmospheric composition, including aerosols, ozone, air pollution, chemical weather, meteorology and scale interaction, climate, climate change and environmental science, including water and energy cycles.