Table of Contents

Abstract: 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 PM_2.5 concentration (~a few percents) but more significant in terms of PM_1.0 (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 PM_2.5 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 PM_2.5 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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 (X_CO2 and X_CH4) 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 X_CO2 and X_CH4 from GOSAT.

Abstract: 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.