Radical initiated secondary aerosol formation—Particle measurements during the 2009 TEXAQS

Particulate matters play important roles in the formation and transformation of ozone. Although photooxidation of volatile organic compounds (VOCs) with respect to ozone formation in the gas phase is well understood, many unknowns still exist in heterogeneous mechanisms that process soot, secondary aerosols (both inorganic and organic), and key radical precursors such as formaldehyde (HCHO) and nitrous acid (HONO). The field data collected in the 2009 Study of Houston Atmospheric Radical Precursors (SHARP), aka, 2009 Texas Air Quality Study (TEXAQS) by our group at the Moody Tower consist of 1) radiometer data to estimate local photolysis rates, 2) instantaneous Lasair particle size distributions, 3) an archive of single particle samples taken with the Time Resolved Aerosol Collector (TRAC) sampler, and 4) hourly OC and EC measurements. The time resolution of the TRAC sampler is 30 minutes for routine measurements, and 15 minutes during some identified “events” (usually in the mid-afternoon) of high ozone and secondary organic or sulfate particle formation. The latter events last typically about an hour. Strong correlation between photochemical activities and organic carbon was observed. Preliminary analysis of our data indicates that secondary organic aerosol is a component of the carbonaceous aerosols observed in Houston. On-going analysis of single particles will reveal more about the composition, sources, and transformation of primary and secondary aerosols initiated by photolysis and subsequent heterogeneous reactions.