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Current atmospheric models do not include secondary organic aerosol (SOA)production from gas-phase reactions of polycyclic aromatic hydrocarbons(PAHs). Recent studies have shown that primary emissions undergo oxidation inthe gas phase, leading to SOA formation. This opens the possibility thatlow-volatility gas-phase precursors are a potentially large source of SOA. Inthis work, SOA formation from gas-phase photooxidation of naphthalene,1-methylnaphthalene (1-MN), 2-methylnaphthalene (2-MN), and1,2-dimethylnaphthalene (1,2-DMN) is studied in the Caltech dual28-m3 chambers. Under high-NOx conditions and aerosol massloadings between 10 and 40 μg m−3, the SOA yields (mass of SOAper mass of hydrocarbon reacted) ranged from 0.19 to 0.30 for naphthalene,0.19 to 0.39 for 1-MN, 0.26 to 0.45 for 2-MN, and constant at 0.31 for1,2-DMN. Under low-NOx conditions, the SOA yields were measured to be0.73, 0.68, and 0.58, for naphthalene, 1-MN, and 2-MN, respectively. The SOAwas observed to be semivolatile under high-NOx conditions andessentially nonvolatile under low-NOx conditions, owing to the higherfraction of ring-retaining products formed under low-NOx conditions.When applying these measured yields to estimate SOA formation from primaryemissions of diesel engines and wood burning, PAHs are estimated to yield3–5 times more SOA than light aromatic compounds over photooxidationtimescales of less than 12 h. PAHs can also account for up to 54% of thetotal SOA from oxidation of diesel emissions, representing a potentiallylarge source of urban SOA

atmospheric chemistry and physics

Secondary organic aerosol formation from photooxidation of naphthalene and alkylnaphthalenes: implications for oxidation of intermediate volatility organic compounds (IVOCs)