Inorganic carbon, atmospheric aerosols

Atmospheric particles in the troposphere are composed of a complex mixture of highly water-soluble inorganic salts, insoluble mineral dust, and carbonaceous material (which includes organic compounds plus elemental carbon) (Jacobson et al., 2000). Studies in which the chemical composition has been determined as a function of particle size demonstrate a correlation between the chemical composition and the size mode of atmospheric aerosols (Meszaros et al., 1997 Krivacsy and Molnar, 1998 Alves et al.,2000 Maenhaut et al.,2002 Smolik et al., 2003 Samara andVoutsa, 2005). 

Particulate emissions are by-products of fuel combustion, industrial processes, and motor vehicles and are believed to have a significant potential for causing adverse health effects. Carbonaceous material present in atmospheric aerosols is a combination of elemental carbon and organic and inorganic compounds. Particulate matter may also consist of fly ash, minerals, or road dust and contain traces of a number of heavy metals. Population-based studies have consistently found that the association between adverse respiratory effects and particulate concentrations occurs in a number of regions throughout the United States. This association is strongest for PM]o and PM2.5 indices (particulate matter less than 10 and 2.5 pm in diameter, respectively). The observed adverse effects include increases in total mortality, mortality due to respiratory and cardiovascular causes, chronic bronchitis, and hospital visits and admissions for asthma. Elderly or unhealthy individuals and infants appear to comprise subpopulations that are most sensitive to the adverse health effects of PM. 

The major constituents of atmospheric particulate soil, dispersed as an aerosol, are carbon soot, organic matter, and inorganic carbonates [5]. The composition of dust collected from air filters is variable it may even vary with the season of the year [6]. 

Carbonic acid. Water in equilibrium with atmospheric CO2 at 25° C has pH 5.65. Natural acidification of precipitation to pH less than 5.65 can occur in remote maritime air masses due to the presence of NH4HSO4 aerosols (Charlson and Rodhe, 1982). In the soil, the partial pressure of CO2 may be 10-100 and up to 400 times greater than that of the atmosphere (Holland, 1978). Given a CO2 pressure 10 or 100 times that of the atmosphere, pH values of 5.15 and 4.65, respectively, are expected. If additional sources of protons are introduced into the soUs, say, from organic or inorganic acids, the pH is depressed further. 

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