6 March 2008
A recently published paper was highlighted in the 18 February 2008 edition of ScienceDaily, an electronic news source that features breaking science news: Cloud Chemistry Concocts Aerosols.
In this paper "Secondary organic aerosol yields from cloud-processing of isoprene oxidation products" published in the 31 January 2008 issue of Geophysical Research Letters, NOAA ESRL scientists in the Chemical Sciences Division and their colleagues at the NOAA Air Resources Laboratory, Rutgers University, and Colorado State University have unveiled additional sources of secondary organic aerosols (SOA) in the atmosphere. Isoprene, the most abundant biogenic hydrocarbon, is emitted from natural sources (some trees and other vegetation) and represents a newly recognized source of atmospheric SOAs. Using model studies based on laboratory experiments, the authors suggest that clouds provide the environment for the transformation of isoprene and its byproducts into aerosol particles. The clouds are able to uptake water-soluble organics formed from isoprene, which are then oxidized within the cloud and form SOAs after cloud droplet evaporation. The authors show that this SOA formation pathway is greatly affected by the amount of nitrogen oxides (NOx) present. These findings can be used to help explain enhanced SOA formation from isoprene in correlation with anthropogenic tracers (NOx). The work thus helps explain why SOA derived from natural emissions (isoprene) have been observed to have a high correlation with anthropogenic pollution.
Background: Incoming solar radiation is scattered by aerosols (atmospheric fine particles), a process that has a cooling effect on global climate. Organic aerosols are classified as "primary" or "secondary." To isolate secondary organic aerosols and the influence they have on global climate is much more elusive than identifying primary aerosols. This is because SOA are not directly emitted, but are formed as a result of reactions of precursors gases in the atmosphere.
Significance: Cloud-derived SOA concentration is boosted as cloud contact-time and liquid water content increase. The authors expect that such information can help improve climate and air quality models. This research contributes to the Air Quality Program within NOAA's Weather and Water Goal and to the Chemical Research and Modeling Program's "Understanding Climate Processes" capabilities within NOAA's Climate Goal.