The Effects of Isoprene in Biogenic New Particle Formation in the Presence of SO2
LEE TISZENKEL, Vignesh Vasudevan Geetha, Shanhu Lee, The University of Alabama in Huntsville
Abstract Number: 402
Working Group: Aerosol Chemistry
Abstract
New particle formation (NPF) from the interactions between biogenic and anthropogenic precursors is responsible for a large portion of atmospheric sub-micron particles. Surveys of the ambient atmosphere have found that NPF seldom occurs when isoprene dominates organic emissions, such as in the southeastern United States or the Amazon. These isoprene-dominant regions are responsible for significant error in NPF modelling due to a lack of comprehensive laboratory data that can explain observations. Previous laboratory investigations of isoprene effects on purely biogenic NPF have found that synergetic effects of isoprene and HOx on monoterpene oxidation contribute to suppression of biogenic NPF. However, pure biogenic nucleation is extremely rare in the real atmosphere due to the ubiquitous presence of anthropogenic pollutants such as sulfur dioxide. We present the results of laboratory studies of isoprene effects on the mixed organic/inorganic system. Particles were produced in a laminar flow reactor from α-pinene oxidation and sulfuric acid. Sulfuric acid was formed in-situ from the reaction of sulfur dioxide with hydroxyl radicals produced from the monoterpene and ozone reaction. Sulfuric acid concentrations were measured with two nitrate CIMS at the beginning and end of the flow tube. Highly-oxidized organic compounds, organosulfates and sulfuric acid clusters were measured with the nitrate HRToF-CIMS at the end of the flow tube. Experiments were done with a fixed α-pinene concentration, with varying sulfuric acid concentration and varying isoprene:α-pinene carbon ratio up to 11, which mimics conditions in the most isoprene-dominant biomes. We found that at sulfuric acid concentrations exceeding 1 pptv, nucleation proceeds at rates similar to purely inorganic nucleation, consistent with previous studies of the mixed organic/inorganic system. At sub-pptv sulfuric acid concentrations, the presence of isoprene suppresses nucleation and growth rates, indicating that biogenic and anthropogenic particle formation processes proceed at similar rates in this regime.