The Ambient Organic Aerosol Soluble in Water: Measurements, Chemical Characterization, and an Investigation of Sources

Abstract

This thesis characterizes the ambient fine organic carbon aerosol and investigates its sources through the development and deployment of new measurement techniques. The focus is on organic compounds that are soluble in water (WSOC), which comprise a large fraction of the organic aerosol, yet little has been known about its chemical nature.

A method was developed for quantitative on-line measurements of WSOC by using a Particle-into-Liquid Sampler (PILS) to capture ambient particles into a flow of purified water, which is then forced through a liquid filter and the carbonaceous content quantified by a Total Organic Carbon (TOC) analyzer. This system allows for a continuous 6 minute (ground-based) or 3 s integrated measurement (airborne) with a limit of detection of 0.1 microgramsC/m3 and uncertainty of 10%.

Furthermore, a new quantitative method was developed to group speciate the WSOC. In the first step, WSOC is separated by use of XAD-8 resin into its hydrophilic (WSOCxp) and hydrophobic (WSOCxr) fractions. This separation can be performed on-line by coupling the XAD-8 column with the PILS-TOC or off-line on WSOC extracted from integrated filter samples. If off-line, a second step involving size-exclusion chromatography (SEC) is used to chromatographically separate by organic functional groups the WSOCxp and recovered hydrophobic fraction (WSOCxrr). During this step, the WSOCxp is further separated into aliphatic acids with less than four carbons, neutrals, and bases. The WSOCxrr can be separated into acids and neutrals.

Results showing the capabilities of the PILS-TOC both on the ground at the St. Louis Midwest Supersite and when airborne during the New England Air Quality Study/Intercontinental Transport and Chemical Transformation 2004 mission conducted in the northeastern U.S. will be presented. Ambient results from urban sites where a PILS-TOC was coupled with a XAD-8 column will be discussed. Data from the two-step speciation performed on samples collected from urban Atlanta summer and winter, and biomass burning in rural Georgia in a region of prescribed burning are presented. Finally, WSOC measurements obtained in Atlanta and its surrounding regions from both the speciation measurements and PILS-TOC will be used to investigate the sources of WSOC in the southeastern U.S.