33. Particulate Matter Organic Acids Measured Using the Particle-into-Liquid Sampler (PILS) at the St. Louis – Midwest Supersite

(1) Environmental Engineering Program, Washington University, Campus Box 1180, One Brookings Drive, St. Louis, MO, 63130/USA

(2) School of Earth & Atmospheric Sciences, 311 Ferst Drive, Georgia Institute of Technology, Atlanta, GA 30332/USA

Sustained particulate matter ion measurements by the Georgia Tech / BNL Particle-Into-Liquid Sampler (PILS) have been conducted at the St. Louis – Midwest Supersite core monitoring location in East St. Louis (IL) since May 2001. In addition to providing semicontinuous data streams for the major ions (sulfate, nitrate, and ammonium), PILS has provided insights into aerosol climatology and atmospheric dynamics for other ionic species. This poster presentation will highlight recent findings on organic acid particulate matter species (formate, acetate, oxalate). For example, in November 2002 we observed a multiday event for fine particulate matter acetate with concentrations following a diurnal profile indicative of formation by secondary processes; these profiles were not observed during other seasons. We conjecture that the meteorological conditions during this late fall time period promoted the acetate particle formation – the summer months favor photochemical production of acetate but the high temperatures favor partitioning to the gas phase, while the winter months feature relatively low photochemical activity towards acetate production. Indeed, during the multiday acetate event the temperatures were cool - normal for this time period - but the solar radiation intensity was relatively high for November. Additional examples will highlight observations for other organic ions.