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Atmospheric oxidation of isoprene and 1,3-Butadiene: influence of aerosol acidity and Relative humidity on secondary organic aerosol
Lewandowski, M., M. Jaoui, J. Offenberg, J. Krug, AND Tad Kleindienst. Atmospheric oxidation of isoprene and 1,3-Butadiene: influence of aerosol acidity and Relative humidity on secondary organic aerosol. Atmospheric Chemistry and Physics Discussions. Copernicus Gesellschaft mbH, Gottingen, Germany, 15:3773-3783, (2015).
The National Exposure Research Laboratory’s (NERL’s) Human Exposure and Atmospheric Sciences Division (HEASD) conducts research in support of EPA’s mission to protect human health and the environment. HEASD’s research program supports Goal 1 (Clean Air) and Goal 4 (Healthy People) of EPA’s strategic plan. More specifically, our division conducts research to characterize the movement of pollutants from the source to contact with humans. Our multidisciplinary research program produces Methods, Measurements, and Models to identify relationships between and characterize processes that link source emissions, environmental concentrations, human exposures, and target-tissue dose. The impact of these tools is improved regulatory programs and policies for EPA.
The effects of acidic seed aerosols on the formation of secondary organic aerosol (SOA)have been examined in a number of previous studies, several of which have observed strong linear correlations between the aerosol acidity (measured as nmol H+ per m3 air sample volume)and the percent change of secondary organic carbon (SOC). The measurements have used several precursor compounds representative of different classes of biogenic hydrocarbons including isoprene, monoterpenes, and sesquiterpenes. To date, isoprene has displayed the most pronounced increase in SOC, although few measurements have been conducted with anthropogenic hydrocarbons. In the present study, we examine several aspects of the effect of aerosol acidity on the secondary organic carbon formation from the photooxidation of 1,3-Butadiene, as well as extending the previous analysis of isoprene. The photooxidation products measured in the absence and presence of acidic sulfate aerosols were generated either through photochemical oxidation of SO2 or by nebulizing mixtures of ammonium sulfate and sulfuric acid into a 14.5 m3 smog chamber system. The results showed that, like isoprene and β-caryophyllene, 1,3-butadiene SOC yields linearly correlate with increasing acidic sulfate aerosol. The observed acid sensitivity of 0.11 %SOC increase per nmol m-3 increase in H+ was approximately a factor of three less than that measured for isoprene. The results also showed that the aerosol yield decreased with increasing humidity for both isoprene and 1,3-butadiene, although to different degrees. Increasing the absolute humidity from 2 to 12 g m-3 reduced the 1,3-butadiene yield by 45% and the isoprene yield by 85%.
LEWANDOWSKI ET AL BDE+ISO ACIDITY V6 REVISED PAPER WT COPYEDITS.PDF (PDF,NA pp, 398.75 KB, about PDF)
Record Details:Record Type: DOCUMENT (JOURNAL/PEER REVIEWED JOURNAL)
Organization:U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AND DEVELOPMENT
NATIONAL EXPOSURE RESEARCH LABORATORY
HUMAN EXPOSURE AND ATMOSPHERIC SCIENCES DIVISION
PROCESS MODELING RESEARCH BRANCH