Organic Particle Functional Groups, Sources, and Oxidation in Houston during TexAQS

Dr. Lynn M. Russell, Professor of Atmospheric Chemistry
Scripps Institution of Oceanography
University of California, San Diego

Organic compounds typically constitute over one-third of the mass of submicron atmospheric particles, which affect the direct and indirect roles of particles on perturbing the Earth's climate. Submicron particles collected on Teflon filters aboard the R/V Ronald Brown during the Texas Air Quality Study and Gulf of Mexico Atmospheric Composition and Climate Study (TexAQS/GoMACCS) 2006 in and around the port of Houston, Texas, were measured by Fourier Transform Infrared (FTIR) and X-ray Fluorescence (XRF) for organic functional groups and elemental composition. Organic mass (OM) concentrations (1 to 25 mg m-3) for ambient particle samples measured by FTIR showed good agreement with measurements made with an Aerosol Mass Spectrometer (AMS). The fractions of organic mass identified as alkane and carboxylic acid groups were 46% and 31%, respectively. Three different types of air masses were identified based on the air mass origin and the radon concentration, with significantly higher carboxylic acid group mass fractions in air masses from the North (33%) than the South (28%) or Gulf (25%). Positive Matrix Factorization (PMF) analysis attributed carboxylic acid fractions of 29-34% to factors with mild or strong correlations (r>0.5) to elemental signatures of oil combustion and 9-23% to wood smoke, indicating that part of the carboxylic acid fraction of OM was formed by the same sources that controlled the metal emissions, namely the oil and wood combustion activities. The implication is that a substantial part of the measured carboxylic acid contribution was formed independently of traditionally "secondary" processes, which would be affected by atmospheric (both photochemical and meteorological) conditions and other emission sources. The carboxylic acid group fractions in the Gulf and South air masses were largely oil combustion emissions from ships as well as background marine sources, with only limited recent land influences (based on radon concentrations). Alcohol groups accounted for 17% of OM (mostly associated with oil combustion emissions and background processed sources), and amine groups accounted for 4-5% of OM in all air masses. Organosulfate groups were found in Gulf and South air masses, accounting for 1% and 3% of OM, respectively. Two-thirds of the OM and oxygen-to-carbon (O/C) measured could be attributed to oil and wood combustion sources based on mild or strong correlations to co-emitted, nonvolatile trace metals, with the remaining one-third being associated with atmospherically-processed organic aerosol. The cloud condensation nuclei (CCN) fraction (normalized by total condensation nuclei) had weak correlations to the alcohol and amine group fractions and mild correlation with O/C, also varying inversely with alkane group fraction. The chemical components that influenced f(RH) were sulfate, organic, and nitrate fraction, but this contrast is consistent with the size-distribution dependence of CCN counters and nephelometers.

Lynn M. Russell is Professor of Atmospheric Chemistry at Scripps Institution of Oceanography on the faculty of University of California at San Diego. She completed her undergraduate work at Stanford University. She received a Ph.D. in Chemical Engineering from the California Institute of Technology for her studies of marine aerosols. Her postdoctoral work as part of the National Center for Atmospheric Research Advanced Studies Program investigated aerosol and trace gas flux and entrainment in the marine boundary layer. Her research is in the area of aerosol particle chemistry, including the behavior of particles in marine and anthropogenically-influenced conditions. This research has been supported by the Dreyfus Foundation, the National Science Foundation, the Office of Naval Research, the National Aeronautics and Space Administration, and the James S. McDonnell Foundation. She received the Whitby Award of the American Association of Aerosol Research in 2003 for her contributions on atmospheric aerosol processes. Her research group at Scripps pursues both modeling and measurement studies of atmospheric aerosols, with a focus on understanding fundamental processes that affect atmospheric aerosols.