Intermediate-volatility organic compounds: a potential source of ambient oxidized organic aerosol.

Smog chamber experiments were conducted to investigate secondary organic aerosol (SOA) formation from intermediate volatility and semivolatile organic compounds (IVOCs and SVOCs). We present evidence for the formation of highly oxygenated SOA from the photooxidation of n-heptadecane, which is used as a proxy for IVOC emissions. The SOA is consistent with multiple generations of oxidation chemistry resulting from OH radical exposure equivalent to approximately 0.5 days of atmospheric processing under high-NO(x) and low-CoA conditions. The SOA has a calculated O/C ratio of 0.59, which is higher than typical for chamber-generated SOA. The mass spectrum of the SOA, as measured with a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS), is similar to the OOA-2 factor determined for Mexico City. SOA formed from the low-NO(x), low-C(OA), oxidation of n-heptadecane is less oxidized because of differences in the chemical mechanism and lower integrated OH exposure. SOA formed from both the oxidation of n-heptadecane under high-NO(x), high-C(OA) conditions and the oxidation of n-pentacosane, a proxy for semivolatile organic emissions, does not produce highly oxygenated SOA, largely because of the condensation of early generation oxidation products.