AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
SOA Formation through Aqueous Chemistry: Volatility and Yields
BARBARA TURPIN, Yong Bin Lim, Diana Ortiz-Montalvo, Allison Schwier, V. Faye McNeill, Rutgers University
Abstract Number: 429 Working Group: Aerosol Chemistry
Abstract Oxidation of organic emissions leads to the abundant formation of small, polar compounds that readily partition into cloud, fog and aerosol waters. Subsequent reactions in the aqueous phase can form low volatility products that remain in the particle phase even after water evaporation. Liquid water is the most abundant condensed phase species in the atmosphere. Thus, gas followed by aqueous chemistry could be a substantial source of secondary organic aerosol (SOAaq). If gas phase production of a water-soluble compound is slow, the compound will be rapidly depleted from the gas phase when it encounters a cloud, and the subsequent aqueous chemistry will proceed as in a batch reactor. If gas-phase production is rapid, that compound will be taken up and present continuously in the aqueous phase with its aqueous products, as in a continuously stirred tank reactor (CSTR).
We used chemical modeling and droplet evaporation experiments to develop insights regarding yields, composition and volatility of SOAaq from aromatic and alkene emissions for these bounding scenarios. Droplet evaporation experiments were conducted using organic mixtures that mimic the aqueous chemical composition predicted by chemical modeling for CSTR and batch reactor scenarios. Monodisperse droplets were generated, evaporated and the resulting particle size was measured. The volatility behavior of mimics was compared with standards with known vapor pressure. Gas-particle partitioning of SOAaq species was also studied using Aerosol Chemical Ionization Mass Spectrometry. Effective heats of vaporization were lower for the complex mixture of organic products than the theoretical values for pure components. Effective vapor pressure was substantially lower when ammonia was added. Modeling results suggest that glyoxal/methylglyoxal SOAaq yields from CSTR scenarios are greater because of oligomerization of unreacted aldehyde; yields of organic acids were virtually identical for batch and CSTR scenarios. Implications to SOAaq formation in clouds and wet aerosols will be discussed.