Submicron aerosols, primary

Primary Submicron Aerosols PAHs and Elemental Carbon... 

The total mass of particulate matter per unit volume of air is perhaps the simplest integral property, and it is on this quantity that U.S. federal standards for particulate pollution have been based. Until recently there was a single primary (health related) standard of 50 g/m (annual geometric mean) and 150 /rg/m- (maximum 24-hr concentration not to be exceeded more than once per year), with an upper cutoff in panicle size of 10 /ttm (PMio). However, epidemiological studies indicate an association between adverse health effects, including enhanced mortality, and submicron aerosol concentrations in many U.S. cities (Pope cl al.. 1995). This has led to the establishment of an additional mass ba.sed standard for particles smaller than 2.5 /im (PMj.j) (U.S. EPA, 1996). There is also a separate health-based standard for lead, one component of the atmospheric aerosol. 

Pj = U for primary chemical components. Coagulation is included in (13.14). which can easily be shown to be a form of the GDE inlegniled over particle mass. Sedimentation is neglected for the submicron range. A time-smoothed conservation equation for the mean square aerosol concentration fluctuations... 

Urban aerosols are mixtures of primary particulate emissions from industries, transportation, power generation, and natural sources and secondary material formed by gas-to-par-ticle conversion mechanisms. The number distribution is dominated by particles smaller than 0.1 /xm, while most of the surface area is in the 0.1 to 0.5 /xm size range. On the contrary, the aerosol mass distribution has usually two distinct modes, one in the submicron regime (referred to as the accumulation mode) and the other in the coarse particle regime (Figure 7.12). 

---