Journal of Geophysical Research: Atmospheres

Cover image for Vol. 122 Issue 10

Impact Factor: 3.454

ISI Journal Citation Reports © Ranking: 2016: 19/85 (Meteorology & Atmospheric Sciences)

Online ISSN: 2169-8996

Associated Title(s): Journal of Geophysical Research

Comparing secondary organicaerosol formation in two U.S. cities

Secondary organic aerosols (SOAs) form from the oxidation of volatile organic compounds (VOCs) in the atmosphere, and the composition and abundance of SOAs affect their effects on air quality, human health, and the planetary radiation budget. To investigate how the production of SOAs varies with location, Zhang et al. (2012) conducted a parallel set of experiments in Los Angeles, Calif., and Atlanta, Ga. Both cities see a large amount of volatile organic compounds thrown into the air because of anthropogenic emissions, largely stemming from vehicles. Atlanta, unlike Los Angeles, also sees a large amount of biogenic emissions from vegetation in the region. To understand how shifts in environmental conditions and the sources of VOCs can affect the resultant SOAs, the authors measured how water-soluble organic compounds partition between gas and particle phases in both Los Angeles and Atlanta. This partitioning reflects the prevalence of the various reaction mechanisms that turn volatile organics into secondary organic compounds. The authors found that in Los Angeles the overall abundance of secondary organics peaked during the day and fell during the night. In Atlanta, however, this diurnal shift was much more muted. By analyzing the gas/aerosol partitioning of nitrate, the authors estimated the effect of changing humidity on the partitioning of volatile organics. They found that in Atlanta, the particulate partition tracked changes in relative humidity, while in Los Angeles there was no such connection. They suggest that the differing sources of VOCs, with Los Angeles being primarily anthropogenic emissions and Atlanta being a mix of anthropogenic and biogenic, lead to the differing SOA daily cycles and partitioning mechanisms.

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