Dear Colleagues,

Air quality has recently received a lot of public interest, not only due to air traffic hazards caused by wildfires or volcanic eruptions, limitation of visibility in National Parks, wilderness and other protected areas, erosion of cultural heritage construction, Arctic haze, and increasing Arctic commercial shipping and cruise-ship traffic as well as Arctic exploration and extraction for fossil resources. The public’s air quality concerns are also motivated by questions regarding the relation of short- and long-term exposure due to various pollutants like ozone, carbon monoxide, black carbon, particulate matter of equal or less than 2.5 µm in diameter (PM_2.5), just to mention a few. Various pollutants have namely been found to be health-adverse, causing asthma, cardio, and even cancerous diseases. Elderly, sensitive people, people with lung- or cardio-related preconditions, and pregnant women are especially at risk for poor air quality related issues. An important aspect of air quality is also the interaction of trace gases and particles with the water and energy cycle via the aerosol impacts on cloud and precipitation formation and reflectivity, as well as water quality in rivers and contaminant input into terrestrial and aqueous ecosystems including the soil and oceans.

This Special Issue about air quality and its impacts on human health as well as water, energy and biogeophysical/biogeochemical cycles will call for submissions of papers that demonstrate the original research that can overcome current gaps in understanding the interactions between air quality and the Earth system. Review articles are also welcome. The topics will include but are not limited to examining the:

1. Relations of air quality and health;
2. impacts of air quality and (Arctic) haze;
3. aerosol–cloud interaction;
4. air quality hazards;
5. air quality climatology and field campaigns; and
6. improvements in air quality modeling including emission modeling and inventories.

Prof. Dr. Nicole Mölders
Dr. Daniele Contini
Dr. Gabriele Curci
Dr. Francesca Costabile
Prof. Dr. Yoshizumi Kajii
Prof. Dr. Prashant Kumar
Dr. Gunnar W. Schade
Dr. Hanwant B. Singh
Dr. Chris G. Tzanis
Prof. Dr. Robert W. Talbot
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Atmosphere is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

• air quality climatology
• air quality change and variability
• longrange transport of air pollutants
• operational air quality monitoring
• air quality field campaigns
• air quality modeling and forecasting
• air quality and health
• emission impacts on weather
• aerosols and clouds
• remote sensing of atmospheric constituents

A Lagrangian Stochastic Particle Trajectory Model (LaStTraM) to Simulate Concentration and Flux Footprints Using the Microclimate Model ENVI-met
Helge Simon *, Jannik Heusinger, Tim Sinsel, Laura Cramer, Stephan Weber, and Michael Bruse
* Geographisches Institut-Geoinformatik, Johannes Gutenberg-Universität Mainz, Germany

Abstract: The number of study sites for the measurement of the surface-energy exchange of energy and greenhouse gases (i.e. carbon dioxide, methane, nitrous oxide) has grown substantially during recent. Flux data is used to increase process understanding of the terrestrial carbon cycle, to constrain models, and to inform policy makers e.g. in the context of climate change research and for modeling purposes. The state-of-the-art method which is used at measurement sites is eddy covariance. For an accurate interpretation of the flux data, it is necessary to estimate the surface area that influences the signal measured at the detector location, which is the so-called flux footprint or flux source area. The concentration or flux footprint of a quantity is a function of the characteristics of the earth surface, the state of the atmosphere as well as the height of the detector above ground level. At the surface, the distribution of sources and sinks (homogenous/heterogeneous), the surface roughness length, and the topography are important factors in shaping the footprint location and dimensions. Atmospheric stability, wind speed and direction as well as turbulent intensity are atmospheric factors influencing the footprint. For this purpose, several models have been published since the 1990s which can be distinguished into four categories: (1) analytical models, (2) Lagrangian stochastic particle dispersion models (LES), (3) large-eddy simulations, and (4) closure models.

Most of the available footprint models are valid only in case of a homogeneous source and in flat topography. This includes all models based on analytically derived mathematical expressions to calculate advection and diffusion of the quantity of interest. LES footprint models and closure models overcome this limitation, i.e., they are able to simulate fluxes in heterogeneous environments, e.g. high vegetation, forests, and urban areas. One characteristic of the first mentioned type of models is the high computational demand. This means that only computer clusters with hundreds of processors are able to calculate footprints in reasonable time. In contrast, Reynolds-Averaged Navier-Stokes (RANS) models have lower computational demand and can hence run on personal computers.

In the present study, the microclimate model ENVI-met, a RANS model, was coupled to a newly developed Lagrangian model called LaStTraM (Lagrangian Stochastic Trajectory Model) to simulate particle trajectories based on the microclimate’s three-dimensional output data. The probability distribution of the particles is calculated using the Lagrangian Stochastic method. Furthermore, it all calculations are running in parallel thus allowing shorter simulation times. An application and evaluation were conducted through a comparison with the commonly used 2D models in two different meteorological cases (stable, unstable) and in three different detector heights. In addition to the comparison with common footprint models, a case study is presented with a simple heterogeneous model domain containing one building and one tree. All examples show good results in comparison to the other models, thus demonstrating LaStTraM’s potential for reliable calculation of footprints homogeneous and heterogenous areas.

Analysis of Spatial-Temporal Pattern of Black Carbon Emission and Dispersion from Biomass Burnings Using Remote Sensing and Monitoring Data in the Greater Metropolitan Region of Sydney
Hiep Nguyen Duc ¹, Kristina Shingles ², David Salter ¹, Gunaratnam Gunashanhar ¹, Matthew Riley ¹, Robert Hynes ¹, and Toan Trieu ^1
1 New South Wales Office of Environment and Heritage, Sydney, Australia
² Department of Environmental Science, Macquarie University, Sydney, Australia  

Abstract: Biomass burnings either due to Hazardous Reduction Burnings (HRBs) in winter or bushfires during summer periods in NSW emit large amount of gaseous pollutants and aerosols which can cause elevated concentrations in metropolitan areas in NSW and beyond. One of the pollutants of concerns is black carbon which is a component of aerosol particles of various sizes and is harmful to health. Remote sensing data from satellites are gradually available for research with rich data sets released on global and local scale as well as aethalometer measurements from a few sites in the OEH network allow researchers to study the emission and dispersion pattern of black carbon in NSW.

This study analyses the characteristics of spatial and temporal patterns of black carbon (BC) in the Greater Metropolitan Region (GMR) of Sydney, Australia, using these data sources as well as dispersion modelling tools available such as HYSPLIT and a WRF-Chem air quality model. The WRF-Chem model is used with FINN (Fire Emission from NCAR) to predict the distribution of BC across the Sydney region during bushfire periods. The prediction of black carbon concentration during a period of bushfires or hazardous reduction burnings (HRBs) from the WRF-Chem air quality model and from MERRA-2 model data is compared with observation data to validate the models.

On the Impact of Trees on Ventilation in a Real Street in Pamplona (Spain)
Jose Luis Santiago ¹, Riccardo Buccolieri ², Esther Rivas ¹, Beatriz Sanchez ¹, Alberto Martilli ¹, Rocio Alonso ¹, Elisa Gatto ² and Fernando Martín ^1
1 Atmospheric Pollution Division, Environmental Department, CIEMAT, Spain
² Dipartimento di Scienze e Tecnologie Biologiche ed Ambientali, University of Salento, Lecce, Italy

Abstract: This paper is devoted to the quantification of changes in ventilation of a real neighbourhood located in Pamplona (Spain) due to street trees. We extend our previous Computational Fluid Dynamics (CFD) modelling study of pollutant dispersion (Santiago et al., 2017, Atmosphere 8, 131) to analyse the variation of street ventilation in several scenarios, accounting for the study street without trees and considering trees with different leaf area density (LAD). Average concentrations at pedestrian level over the whole neighbourhood and over the study street, and wind speed, flow rates and total pollutant fluxes across lateral sides and top of the street are computed to evaluate changes between the different scenarios. Additionally, wind flow and vertical profiles of average flow properties and concentration over the study street are analysed. Accounting for inlet wind flow is almost perpendicular to the study street (prevailing wind direction), results show that as LAD increases, average concentration in the whole neighbourhood due to a decrease of wind speed. On the other hand, the inclusion of trees in a street produces an increase of average pollutant concentration only within this street (not for the whole neighbourhood), in particular for the scenario with highest LAD. New trees with the highest LAD notably change the ventilation of the street producing an increase of total pollutant fluxes inward the street. Additionally, pollutant dispersion within the street is modified reducing the wind speed parallel to the street and turbulent kinetic energy within vegetation canopy. Therefore, changes on street ventilation induced by new trees produce variation of pollutant fluxes inward the street, which could be emitted in other streets, and dispersion of pollutant released within the street, and consequently produces change in average concentration.

Decadal Trends and Variability in Intermountain West Surface Ozone near Oil and Gas Extraction Fields
Ying Zhou ¹, Huiting Mao ¹ and Barkley C. Sive ^2
1 Department of Chemistry, State University of New York, Syracuse, NY 13210, USA
² National Park Service, Air Resources Division, Lakewood, CO 80225, USA

Abstract: Decadal trends in surface ozone (O3) were studied for the U.S. Intermountain West over 2005 – 2015. Widely disparaging trends, or a lack thereof, were found at 8 sites in/near oil and natural gas (O&NG) basins resulting from different controlling factors rather than a simplistic, uniform one. The decreasing trends at Mesa Verde National Park (−0.83 ppbv/yr) and Canyonlands National Park (-0.58 ppbv/yr) were driven by decreased natural gas production and decreased emissions from coal-fired electricity generation nearby. The trend at Wind Cave National Park (−1.16 ppbv/yr) resulted from reduced solar radiation due to increasingly frequent precipitation weather. The lack of trends at the remaining sites was likely caused by the increasing O&NG emissions and decreasing emissions from other anthropogenic activities. Wintertime atmospheric stagnant conditions, often with occurrence of high O₃, were associated with the Arctic Oscillation (AO). Emission reductions of volatile organic compounds (VOCs) and NO_X during negative AO years and VOC emission reductions alone in positive AO years could effectively mitigate high wintertime O₃ within the O&NG basins, as indicated by box model simulations. Our findings suggest that emissions from O&NG extraction activities could alter decadal trends in Intermountain West O₃ design values and hence warrant consideration in developing efficient O₃ mitigation strategies for the Intermountain West.

Effects of Spring Agricultural Fires on Air Quality in Ontario
Corresponding author: Frank Dempsey
Ontario Ministry of the Environment, Conservation and Parks, Canada

Abstract: Agricultural burning of crop debris in fields produces plumes of smoke and combustion products that may be transported long distances and then be detected by ground-level air quality monitoring stations. In Ontario, Canada, smoke plumes have been detected whose origins can be shown to be agricultural burning in regions far to the south or west of Ontario. Effects on air quality include anomalously high concentrations of ozone during several days coincident with increased concentrations of PM_2.5 or nitrogen dioxide. While these events occur each year during the warm season, the examples presented in this study occurred during the month of April during various years, when forest fires are unlikely, ozone concentrations rarely exceed 50 ppb, and atypically high concentrations of ozone (in the range of 70-90 ppb) were clearly anomalous.

Long-Term Characterisation of Submicron Atmospheric Particles in a Urban Background Site in Southern Italy
Adelaide Dinoi, Marianna Conte, Fabio M. Grasso, Daniele Contini *
Institute of Atmospheric Sciences and Climate, ISAC-CNR, 73100 Lecce, Italy

Abstract: There is an increasing evidence that submicron atmospheric particles (<1 µm diameter) play a decisive role in air quality being related to toxicological effects. In addition to long-range contribution, submicron particles are produced from several local sources, including vehicular traffic, one of the most important sources in urban areas, and biomass burning. Furthermore, gas-to-particle conversion processes strongly influence atmospheric concentrations and size distributions. Temporal and spatial variations of size distributions and number concentrations are commonly related to meteorological conditions that regulate the remarkable differences observed during the hours of the day and in different periods of the year. Information on the long-term behavior of particle number size distributions is still scarce, especially in Southern Italy, therefore this study aims to offer a better understanding of the processes controlling the dynamics of atmospheric particles in this area.

Continuous measurements of number size distributions of particles in the size range from 10 to 800 nm were carried out by a scanning mobility particle sizer (SMPS). The measurements were performed from 2015 to 2019 at the Environmental Climate Observatory (ECO) of Lecce, a regional station of GAW/ACTRIS program. The observatory is located on the roof of the ISAC-CNR Institute, inside the University Campus, in a urban background site influenced by direct emission of road traffic and biomass burning. The main objectives were to investigate and evaluate diurnal, weekly and seasonal trends of particle number concentrations, number size distributions, and modal structure of aerosol particles. Meteorological parameters, measured on-site, together with back-trajectory analysis were also taken into account to investigate the impact of circulation of air masses on observed trends.

Bacteria as Cloud Condensation Nuclei (CCN) in the Atmosphere
Mihalis Lazaridis
School of Environmental Engineering, Technical University of Crete, Greece

Abstract: Bacteria activation and Cloud Condensational Nuclei (CCN) formation has been studied in the atmosphere using the classical theory of heterogeneous nucleation. Simulations were performed for the binary system of sulfuric acid – water using laboratory determined contact angles. Realistic model simulations were performed at different atmospheric heights for a set of 140 different bacteria. Model simulations showed that bacteria activation is a potential favorable process in the atmosphere which may enhanced at lower temperatures. CCN formation from bacteria nuclei is dependent on ambient atmospheric conditions (temperature, relative humidity), bacteria size and sulfuric acid concentration. Furthermore, a critical parameter for the determination of bacteria activation is the value of the intermolecular potential between the bacteria’s surface and the critical cluster formed at their surface. In the classical nucleation theory this is parameterized with the contact angle between substrate and critical cluster. Therefore, the dataset of laboratory values of contact angle of water on different bacteria substrates needs to be enriched for realistic simulations of bacteria activation in the atmosphere.

Characterization of the Global Sources of Atmospheric Nitric Oxide from Agricultural Soils
Corresponding author: Viney P. Aneja
Department of Marine, Earth, and Atmospheric Sciences, North Carolina State University, USA

Bias Correction of Operational Air Quality Forecast with Near Real-Time Observations and Machine Learning
Corresponding author: Gabriele Curci
Dipartimento di Scienze Fisiche e Chimiche-CETEMPS, Universita' degli Studi dell'Aquila, Italy

Water-Soluble Dicarboxylic and W-oxocarboxylic Acids in Size-Segregated Aerosols over Northern Japan: Sources and Formation Processes
Dhananjay K. Deshmukh, Kimitaka Kawamura and Minoru Kobayashi
Chubu Institute for Advanced Studies, Chubu University, Japan

Air quality Deterioration by Biomass Burning for Heating and Cooking
Maria Kanakidou
Environmental Chemical Processes Laboratory, University of Crete, Greece

T. Nishanth, M. K. Satheesh Kumar and Kalliat T. Valsaraj *
* Cain Department of Chemical Engineering, Louisiana State University, Baton Rouge, LA 70803, USA 

Francesca Costabile
ISAC-CNR, Italy

Monoterpene-Derived Organic Nitrates Contribute to Nighttime Aerosol Formation in a Mixed, Deciduous Forest
Robert J. Griffin
George R. Brown School of Engineering, Rice University, USA

Title: TBD
Francesca Costabile
ISAC-CNR, Italy

Title: TBD
Francesca Costabile
ISAC-CNR, Italy