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Atmospheric Effects
Published in Wayne T. Davis, Joshua S. Fu, Thad Godish, Air Quality, 2021
Wayne T. Davis, Joshua S. Fu, Thad Godish
Atmospheric particles can serve as sites for condensation of H2O vapor. Condensation around nucleating particles is an important factor in cloud development and precipitation. Only a small fraction of the total aerosol load of the atmosphere serves as weather-active or cloud condensation nuclei (CCN).
Particulate matter
Published in Abhishek Tiwary, Ian Williams, Air Pollution, 2018
The condensation particle counter (CPC, also known as the condensation nucleus counter (CNC) or Aitken nucleus counter) is used to measure the total number concentration of particles in the diameter range from a few nanometres to 1 μm. The particles are introduced into a chamber where they are exposed to a water- or alcohol-based supersaturated vapour. The particles act as condensation nuclei for droplets that grow to around 10 μm diameter, when they are large enough to be detected and counted, usually by optical methods. As the growth is diffusion-limited, all the droplets are of similar diameter even if the original particles were highly polydisperse. Because the supersaturation is very high, it makes no difference what the original particle was made of – it simply serves as a condensation centre. In some designs the supersaturation is created cyclically by adiabatic expansion, and in some it is created continuously by conduction cooling. Individual particles can be counted if the concentration is low enough. At higher concentrations an optical method based on attenuation of a beam by the droplet cloud is used. Problems may be caused by excessive concentrations of nanoparticles (<20 nm), which are undercounted because the vapour has been depleted. An adaptation of this technique is used to count cloud condensation nuclei (CCN) particles. These are activated by the low supersaturations (0.01%–1%) found in updrafts and clouds. The controlled supersaturation is achieved by maintaining two wetted surfaces at different temperatures.
Atmospheric Chemistry, Measurements, and Models
Published in Winston Chow, Katherine K. Connor, Peter Mueller, Ronald Wyzga, Donald Porcella, Leonard Levin, Ramsay Chang, Managing Hazardous Air Pollutants, 2020
Peter W. Sage, Peter K. Mueller
The recent emergence of the following issues provides impetus for furthering our knowledge of atmospheric chloride compounds: Air toxics. This is the most important issue because the Clean Air Act Amendments of 1990 designate HCl as a hazardous air pollutant (HAP or an “air toxic"). To be able to relate emission rates of HCl to ambient concentrations and human health risks requires an understanding of the formation and removal mechanisms in the atmosphere as well as its toxicity. Moreover, because in the atmosphere chloride salts are converted into HCl and vice versa (as discussed below), the health hazards of anthropogenic HCl emissions ought to be assessed within the context of the total HCl and chloride emissions from all sources.Atmospheric acidity, aerosols, and visibility. Comparing maximum 24-h concentrations (in moles per cubic meter of air volume) from a 1-year data set for the Los Angeles area, HCl concentrations are 30 to 120% of HNO3 concentrations.3 Whereas HNO3 — the predominant gaseous inorganic acid in the Los Angeles area — is produced from atmospheric transformations of NOx emissions, no large anthropogenic sources of HCl are known to exist in the area. It is widely accepted that the reactions of nitric and sulfuric acid with sea-salt aerosols generate HCl in coastal environments.4,9 Given that chloride salts are present not only in sea salt but also in primary particulate matter emissions from natural (e.g., soil dust) and anthropogenic sources, the importance of HCl displacement reactions to ambient acidity and aerosol properties needs to be assessed. For some areas, an adequate representation of gas- and particle-phase chlorides may be necessary in air quality models when these models are used to address atmospheric acidity and visibility.Climate and cloud condensation nuclei (CCN). It has been postulated that sulfate aerosols — formed by the oxidation of oceanic dimethyl sulfide (DMS) and/or anthropogenic SO2 — are important contributors to CCN, which influence the earth’s radiation budget and, hence, climate.10–13 Because chlorides are ever present in marine environments, their presence and interactions, particularly with sulfur compounds, ought to be considered in delineating the linkage between climate and CCN. For instance, the oxidation of SO2 — an intermediate product of DMS-to-sulfate conversion14 — can be catalyzed by chloride ions.15
Organic composition of three different size ranges of aerosol particles over the Southern Ocean
Published in Aerosol Science and Technology, 2020
G. Saliba, K. J. Sanchez, L. M. Russell, C. H. Twohy, G. C. Roberts, S. Lewis, J. Dedrick, C. S. McCluskey, K. Moore, P. J. DeMott, D. W. Toohey
Aerosol-cloud interactions are poorly understood and are the leading source of uncertainty for the top-of-the-atmosphere aerosol radiative forcing (Stocker et al., 2013). Depending on their size and chemical composition particles can act as cloud condensation nuclei (CCN) on which cloud droplets form, affecting cloud brightness and precipitation patterns (Andreae and Rosenfeld 2008). Oceans cover about 70% of Earth and their dark surfaces makes the radiative impacts of clouds particularly important. This is especially relevant over the Southern Ocean (SO), which is the cloudiest region on Earth, as cloud properties are sensitive to aerosol concentrations (Whittlestone and Zahorowski 1998). The often low particle number concentrations in the SO marine boundary layer (MBL) and the remote location of the SO, where the aerosol is minimally perturbed from anthropogenic influence, provide a unique environment to investigate the radiative impacts of aerosol particles (Gabric, Whetton, and Cropp 2001; Ayers and Gillett 2000; Andreae et al. 1999; Quinn et al. 1998).
Trajectory-based analysis on the source areas and transportation pathways of atmospheric particulate matter over Eastern Finland
Published in Tellus B: Chemical and Physical Meteorology, 2020
Olli Väisänen, Liqing Hao, Annele Virtanen, Sami Romakkaniemi
Atmospheric aerosol particles comprise complex mixtures of various organic and inorganic chemical constituents. The aerosol chemical composition is a crucial factor determining particles’ fate and role in the atmosphere, and most notably, their impact on climate. Most of the aerosol types present in the atmosphere tend to cool the climate by reflecting the solar shortwave radiation back to space. In addition, depending on the prevalent meteorological conditions, particles of certain size and chemical composition can act as condensation nuclei for cloud droplets. Therefore, increasing the number of available cloud condensation nuclei (CCN) could potentially lead to increase in cloud droplet concentration, which directly increases cloud albedo (Twomey, 1974), and initiates several potential feedback processes affecting not only cloud microphysical properties but also thickness and mesoscale cloud coverage (Albrecht, 1989; Haywood and Boucher, 2000; Lohmann and Feichter, 2005; Quaas et al., 2020).
Factors affecting the formation of alpha and beta polymorphs in glutaric acid aerosols
Published in Aerosol Science and Technology, 2019
Phoebe C. Belser, Hemanta R. Timsina, Timothy M. Raymond, Dabrina D. Dutcher
To accurately model climate and the atmosphere, the behavior of aerosols must be well understood. The presence of aerosols in the atmosphere plays a large role in cloud formation and therefore climate forcing. Clouds and aerosols are the largest sources of uncertainty in the understanding of climate change (Boucher 2013). These organic aerosols typically make up 20%–80% of the fine particles (by mass) in the atmosphere (Goldstein et al. 2008; Saxena and Hildemann 1996). Within the atmosphere, aerosols have three significant functions. The first is the direct effect, which is aerosols’ ability to scatter light. The indirect aerosol effect is the aerosols' cloud condensation nuclei (CCN) activity or their ability to take on water to form clouds. Lastly, the aerosols play a large role in atmospheric chemistry (Seinfeld and Pandis 2016).