Isoprene Forms Secondary Organic Aerosol Through Cloud Processing: A Model Study
Abstract
Cloud processing of water-soluble organic vapors has been proposed as a pathway for the formation of organic particulate matter (PM) in the atmosphere (i.e., secondary organic aerosol; SOA). The simulations described below suggest that cloud processing of isoprene is a substantial contributor to atmospheric oxalic acid and SOA formation. Isoprene, a biogenic volatile organic compound (VOC) of global importance, forms highly water-soluble glyoxal, methylglyoxal, and glycolaldehyde in the gas phase. These carbonyls favorably partition into cloud droplets where they oxidize to organic acids (e.g., glyoxylic acid, glycolic acid, pyruvic acid, and oxalic acid). In this study we developed a box model to examine the importance of isoprene chemistry to in-cloud formation of SOA. The box model incorporates gas- and aqueous-phase chemistry and phase transfer of relevant water-soluble species. Simulations were conducted under clean conditions typical of the tropical Amazon (i.e., high emission flux of isoprene and low emissions of anthropogenic pollutants). Simulation results show that isoprene forms a substantial amount of organic acids through cloud processing. More than 80% of oxalic acid is expected to remain in the particle phase after cloud evaporation. This study suggests that cloud processing of isoprene is a substantial contributor to atmospheric water-soluble SOA that can alter the microphysics of cloud condensation nuclei (CCN). This work also discusses the sensitivity of the model to important model parameters.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2004
- Bibcode:
- 2004AGUFM.A21C0753L
- Keywords:
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- 0305 Aerosols and particles (0345;
- 4801);
- 0317 Chemical kinetic and photochemical properties;
- 0320 Cloud physics and chemistry;
- 0368 Troposphere: constituent transport and chemistry