Summary of Key Points • Secondary organic aerosol from isoprene, monoterpenes, sesquiterpenes, and aromatics contributes substantially to organic carbon in PM 2.5 in the eastern U.S. mainly during the summer. Other U.S. areas under study. • Aromatic contribution higher than typically predicated in air quality models. • Organic carbon in PM 2.5 was found to range from 2 – 5 μgC m -3 throughout the year with primary sources dominating in the winter and SOC dominating during the summer. Primary and secondary contributions can be offsetting leading to minor seasonal trends. • Estimates of SOC contribution from biogenic HC precursors found to be substantially greater than anthropogenic HC precursors in the eastern U.S. • Results consistent with SOC contributions to the organic carbon measured in laboratory mixtures and with 14 C data measured in laboratory experiments and from 14 C in field studies.
Next Steps • Conduct studies combining both CMB analysis for primary compounds and mass fractions for secondary compounds to see the degree of consistency between SOA and “other OC” from the CMB analysis. • Look at alternative double derivative technique to improve sensitivity of tracers from aromatic hydrocarbons. • Use information from laboratory and field studies to provide basis for an improved SOA module for CMAQ. • Determine tracers compounds from other classes of possible SOA producing hydrocarbons, such as, high MW alkanes, etc. • Determine tracer compounds from additional high volume aromatic hydrocarbons (e.g., m-xylene, 1,2,4-TMB) and sesquiterpenes (e.g., α- humulene, α-farnesene). • Examine SOA production from complex mixtures. • Further study role of acid-catalysis on SOA formation and possible tracer compounds produced.