AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Unresolved Complex Mixture Emissions from Combustion Sources and Their Potential to Form Secondary Organic Aerosol
SHANTANU JATHAR, Havala Pye, Peter Adams, Allen Robinson, Carnegie Mellon University
Abstract Number: 308 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract The Center for Atmospheric Particle Studies (CAPS, Pittsburgh PA) has undertaken numerous studies to investigate secondary organic aerosol (SOA) formation from various combustion sources (aircraft, gasoline and diesel light-duty vehicles, biomass). Across the different sources, we make two robust conclusions. One, a significant fraction of the gas- and vapor-phase organic emissions remain unspeciated or unresolved; these include semi-volatile and intermediate volatility organic compounds and are referred to as an unresolved complex mixture (UCM) And two, after a few hours of photochemical processing, SOA accounts for a significant fraction of the (primary+secondary) aerosol mass, most of which cannot be explained by speciated SOA precursors. We hypothesize that the unexplained SOA arises from the gas-phase oxidation of these UCM emissions. In this work, we propose a simple method to model SOA formation from UCM emissions and use it to quantify UCM’s influence on the regional and global SOA budget.
The UCM SOA is parameterized similar to the SOA formation from single species like benzene or alpha-pinene, where the UCM is considered as a single species. We estimate that at atmospherically relevant organic aerosol concentrations (5-20 microgram per cubic-metre), gasoline vehicle, diesel vehicle, aircraft and biomass burning emissions have a substantial SOA yield (10-30%). We use three independent sources (Schauer et al., 1999-2002, EPA’s SPECIATE, CMU) to estimate UCM emissions from combustion sources. Globally, we find that UCM emissions could be two-thirds of total anthropogenic SOA precursor emissions (~33 Tg/yr). If these UCM emissions were included in existing SOA models (very few of which explicitly account for UCM emissions), a simple calculation suggests that it could result in doubling the anthropogenic SOA production worldwide.