Overview of Secondary Organic Aerosol Formation Pathways

1 Overview of Secondary Organic Aerosol Formation Pathways 

Secondary organic aerosol material is formed in the atmosphere by the mass transfer to the aerosol phase of low vapor pressure products of the oxidation of organic gases. As organic gases are oxidized in the gas phase by species such as the hydroxyl radical (OH), ozone (03), and the nitrate radical (N03), their oxidation products accumulate. Some of these products have low volatilities and condense on the available particles in an effort to establish equilibrium between the gas and aerosol phases. 

The mass transfer flux of these products to the aerosol phase, J will be proportional to the difference between their gas-phase concentration cg and their concentration in the gas phase at the particle surface ceq  

FIGURE 14.11 Proposed gas-phase reaction mechanism for the cyclohexene-ozone reaction. 

The preceding description of aerosol formation from the cyclohexene-ozone reaction reflected the presumed mechanism of secondary organic aerosol formation for a number of years. In actuality, when organic species are already present in particles, as they frequently 

TABLE 13.10 Products of the Cyclohexene-Ozone Gas-Phase Reaction 

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