Primary emission sources due to human activity have increased over geogenic sources by a factor of 2 15, which is larger than the aforementioned factor of 3 average increase in Hg deposition.
These appear to correspond to the time scale of (1) the reduction in the original FDNPP accident surge (primary emission source), (2) the tropospheric transportation and diffusion of the radioactive plume (equivalent to the removal of radioactive aerosols from the atmosphere), and (3) the emission intensity of re-suspension (secondary emission sources).
Fossil fuel combustion is the main emission source for gas pollutants, such as NOX, SO2 and CO2, and coal is now a primary energy source used worldwide with coal combustion being the greatest atmospheric pollution source in China.
Nitro-PAHs (NPAHs), which are nitro-derivatives of PAHs, also are widely distributed in the environment, and result from both primary emissions from combustion sources and atmospheric transformations of PAHs.
It is possible that PM2.5, which originates from primary emissions from combustion sources and from secondary formation in the atmosphere, has different chronic health impacts than larger coarse particles (PM with aerodynamic diameters between 2.5 and 10 μm; PM10 2.5) because of their different composition.
This is largely because many primary CO2 emission sources co-emit aerosols with CO2.
Emission inventories suggest that motor vehicles are the primary direct emission sources of fine and UFPs to the atmosphere in urban areas (Hitchins et al. 2000; Zhu et al. 2002b).
Estimates of Hg emissions to the atmosphere are depicted in Figure 1, based on Holmes et al. Primary emissions include natural geogenic sources (volcanism and erosion; estimated at 500 Mg a 1) and anthropogenic sources (fuel combustion, waste incineration, and mining; 2100 Mg a 1).
Because there are few other sources of primary emissions of carbonaceous material such as coal and fuel oil combustion in California, approximately 80% or more of the EC is derived from diesel exhaust (Schauer and Cass 2000).
We classified compounds based on the availability of concentration data, emissions sources, and the primary route of exposure.
