The acidity of atmospheric particles and clouds

Acidity, defined as pH, is a central component of aqueous chemistry. In the atmosphere, the acidity of condensed phases (aerosol particles, cloud water, and fog droplets) governs the phase partitioning of semivolatile gases such as HNO3, NH3, HCl, and organic acids and bases as well as chemical reac...

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Veröffentlicht in:	Atmospheric chemistry and physics Jg. 20; H. 8; S. 4809 - 4888
Hauptverfasser:	Pye, Havala O. T., Nenes, Athanasios, Alexander, Becky, Ault, Andrew P., Barth, Mary C., Clegg, Simon L., Collett Jr, Jeffrey L., Fahey, Kathleen M., Hennigan, Christopher J., Herrmann, Hartmut, Kanakidou, Maria, Kelly, James T., Ku, I-Ting, McNeill, V. Faye, Riemer, Nicole, Schaefer, Thomas, Shi, Guoliang, Tilgner, Andreas, Walker, John T., Wang, Tao, Weber, Rodney, Xing, Jia, Zaveri, Rahul A., Zuend, Andreas
Format:	Journal Article
Sprache:	Englisch
Veröffentlicht:	Germany Copernicus GmbH 24.04.2020 Copernicus Publications, EGU Copernicus Publications
Schlagworte:	Acidity Aerosol particles Aerosols Air pollution Air pollution control Ammonia Analysis Anthropogenic factors Atmosphere Atmospheric chemistry Atmospheric processes Buffers (chemistry) Chemical reactions Cloud droplets Cloud water Clouds Clouds (Meteorology) Droplets Dust Emissions Estimates Fog Fog droplets Gases Health Influence INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY Nature Nitrates Nitrogen Nitrogen oxides Nomenclature Nutrients Organic acids Oxides Particulates pH effects Photochemicals Pollutant deposition Pollutants Productivity Sulfur Sulfur compounds Sulphur Terrestrial ecosystems Thermodynamic models Thermodynamics United States > US
ISSN:	1680-7324, 1680-7316, 1680-7324
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Zusammenfassung:	Acidity, defined as pH, is a central component of aqueous chemistry. In the atmosphere, the acidity of condensed phases (aerosol particles, cloud water, and fog droplets) governs the phase partitioning of semivolatile gases such as HNO3, NH3, HCl, and organic acids and bases as well as chemical reaction rates. It has implications for the atmospheric lifetime of pollutants, deposition, and human health. Despite its fundamental role in atmospheric processes, only recently has this field seen a growth in the number of studies on particle acidity. Even with this growth, many fine-particle pH estimates must be based on thermodynamic model calculations since no operational techniques exist for direct measurements. Current information indicates acidic fine particles are ubiquitous, but observationally constrained pH estimates are limited in spatial and temporal coverage. Clouds and fogs are also generally acidic, but to a lesser degree than particles, and have a range of pH that is quite sensitive to anthropogenic emissions of sulfur and nitrogen oxides, as well as ambient ammonia. Historical measurements indicate that cloud and fog droplet pH has changed in recent decades in response to controls on anthropogenic emissions, while the limited trend data for aerosol particles indicate acidity may be relatively constant due to the semivolatile nature of the key acids and bases and buffering in particles. This paper reviews and synthesizes the current state of knowledge on the acidity of atmospheric condensed phases, specifically particles and cloud droplets. It includes recommendations for estimating acidity and pH, standard nomenclature, a synthesis of current pH estimates based on observations, and new model calculations on the local and global scale.
Bibliographie:	ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 14 content type line 23 Natural Sciences and Engineering Research Council of Canada (NSERC) AC05-76RL01830; AGS-1650786; CHE-1454763; CHE-1654149; AGS-1254428; AGS-644998; 1852977; T24-504/17-N; 726165; RGPIN/04315-2014; PANACEA MIS 5021516 Greece and European Union European Regional Development Fund USDOE National Science Foundation (NSF) Hong Kong Research Grants Council European Research Council (ERC) PNNL-SA-148049 Author contributions. HOTP provided overall project coordination including preparation and finalization of synthesized drafts. HOTP and AN designed the overall scope of this study. AN coordinated the supplement. JW and JK led Sect. 1 on the importance of acidity with contributions from AN. AZ led Sect. 2 on definitions of pH. CH led Sect. 3 on proxies of pH. AN led Sect. 4 on the box model intercomparison. Section 4 contains significant portions of text originally created by the Sect. 2 (idealized scenario calculations) and Sect. 3 (proxy calculations) teams. VFM led Sect. 5 on the role of kinetics and mechanisms of pH. RAZ led Sect. 6 on the role of particle size and mixing state. MK and AN led Sect. 7.1 on observations of atmospheric particle pH. JC led Sect. 7.2 on observations of cloud water pH. HOTP led Sect. 8 on large-scale model predictions of pH. Major messages (Sect. 9) written by AN, were created at a workshop organized by HOTP and hosted at EPA in Research Triangle Park. Authors prepared text, figures, and tables in collaboration.
ISSN:	1680-7324 1680-7316 1680-7324
DOI:	10.5194/acp-20-4809-2020