Health Assessment Document for Diesel Emissions - NSCEP | US ...

1 pollutants depends on the amount of time a specific pollutant resides in the atmosphere and is
2 available for dispersion (Schroeder and Lane, 1988). As primary diesel emissions are a very
3 complex mixture containing thousands of organic and inorganic constituents in the gas and
4 particulate phases that have different chemical reactivities, they are removed by dry and wet
5 deposition processes at different rates. The more reactive compounds with short lifetimes will be
6 removed from the atmosphere relatively quickly; whereas more stable pollutants can be
7 transported over greater distances. Clearly, a knowledge of the atmospheric loss processes and
8 lifetimes for automotive emissions is important, because these lifetimes determine the geographic
9 extent of the influence of these emissions.
1 0 Anthropogenic pollutants can travel through the atmosphere over long distances. In
11 particular, the long-range transport of so2 and its transformation to so; have been studied
12 · extensively (Galloway and Whelpdale, 1980; Lowenthal and Rahn, 1985). The organic
13 pollutants, particularly those adsorbed on carbonaceous particles, are also subjected to long-range
14 transport. Organic compounds, such as P AHs, adsorbed on diesel particulate matter are generally
15 more resistant to atmospheric reactions than those in the gas phase. In addition, particles of
16 smaller diameter (