Organic matter major contributors

The concentration of atmospheric aerosols varies considerably in space and time. This variability of the aerosol concentration field is determined by meteorology and the emissions of aerosols and their precursors. For example, the annual average concentration of PM2.5 in North America varies by more than an order of magnitude as one moves from the clean remote to the polluted urban areas of Mexico City and southern California (Figure 8.24). Sulfate dominates the fine aerosol composition in the eastern United States, while organics are major contributors to the aerosol mass everywhere. Nitrates are major components of the PM2.5 in the western United States. The EC makes a relatively small contribution to the particle mass in many areas, but because of its ability to absorb light and its toxicity, it is an important component of atmospheric particulate matter. 

Other major contributors to TSP (not measured) are sulfates, organic matter, and water. 

There is one further major contributor to sedimentary organic matter, bacteria. A large proportion of the energy flow in ecosystems can pass through the detrital food chain, in which heterotrophic bacteria are prominent participants. Heterotrophic bacteria are important in all sedimentary environments, and although they consume organic detritus they supplement the organic matter with their own remains. In some environments autotrophic bacteria may also be important (e.g. the Black Sea see Section 3.4.3c). 

Emissions from motor vehicles are among the major contributors to fine particle concentrations in the urban atmosphere (Schauer et al. 1996 Kleeman et al. 2000) they make substantial direct and indirect contributions to ambient PM levels. Direct particulate emission sources from vehicles include their exhaust (Mulawa et al. 1997 Sagebiel et al. 1997), the mechanical wear of tires and brakes (Rogge et al. 1993 Garg et al. 2000), and the ejection of particles from the pavement (Kupiainen et al. 2005) and unpaved road shoulders (Moosmiiller et al. 1998) as well as re-suspension processes (Nicholson et al. 1989 Stembeck et al. 2002). Indirect contributions include the emission of reactive gases, both organic and inorganic, which form secondary particulate matter via atmospheric transformations. 

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