A Study on Photo-Oxidation Under High-Nox Conditions Forming Secondary Organic Aerosols From Isoprene

DOI : http://dx.doi.org/10.13005/msri/060119

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The oxidation of isoprene (2-methyl-1,3-butadiene) is known to play a central role in the photochemistry of the troposphere, but is generally not considered to lead to the formation of secondary organic aerosol (SOA), due to the relatively high volatility of known reaction products. However, in the chamber studies described here, we measure SOA production from isoprene photo-oxidation under high-NOx conditions, at significantly lower isoprene concentrations than had been observed previously. Mass yields are low (0.9-3.0%), but because of large emissions, isoprene photo-oxidation may still contribute substantially to global SOA production. Results from photo-oxidation experiments of compounds structurally similar to isoprene (1,3-butadiene and 2- and 3-methyl-1-butene) suggest that SOA formation from isoprene oxidation proceeds from the further reaction of first-generation oxidation products (i.e., the oxidative attack of both double bonds). The gas-phase chemistry of such oxidation products is in general poorly characterized and warrants further study.

Photo-oxidation; isoprene; NOx; Secondary organic aerosols