A review of Secondary Organic Aerosol (SOA) formation from isoprene

Abstract

Recent field and laboratory evidence indicates that the oxidation of isoprene, (2-methyl-1,3-butadiene, C5H8) forms secondary organic aerosol (SOA). Global biogenic emissions of isoprene (600 Tg yr 1 are sufficiently large that the formation of SOA in even small yields results in substan- tial production of atmospheric particulate matter, likely hav- ing implications for air quality and climate. Here we present a review of field measurements, experimental work, and modeling studies aimed at understanding the mechanisms, yield, and atmospheric importance of isoprene-derived SOA. SOA yields depend on a number of factors, including organic aerosol loading (Mo), NOx level (RO2 chemistry), and, be- cause of the importance of multigenerational chemistry, the degree of oxidation. These dependences are not always in- cluded in SOA modules used in atmospheric transport mod- els, and instead most yield parameterizations rely on a single set of chamber experiments (carried out over a limited range of conditions); this may lead to very different estimates of the atmospheric importance of isoprene SOA. New yield param- eterizations, based on all available laboratory data (Mo=0 50 µg m 3 are presented here, so that SOA formation may be computed as a function of Mo, NOx level, and tempera- ture. Current research needs and future research directions are identified.

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