Organic composition of single and submicron particles in different regions of western North America and the eastern Pacific during INTEX-B 2006

摘要

Single particles were collected from an aircraft platform as part of theIntercontinental Chemical Transport Experiment – Phase B (INTEX-B) conductedover the eastern Pacific and western North America. Single particle spectrawere obtained using scanning transmission X-ray microscopy-near edge X-rayabsorption fine structure spectroscopy (STXM-NEXAFS). Bulk submicronparticles were also collected and organic functional group and elementalconcentrations were quantified with Fourier transform infrared (FTIR)spectroscopy and X-ray fluorescence (XRF). Single particle spectra wereclassified into metaclasses associated with different sources and atmosphericprocessing. Particles with spectra indicative of secondary organic aerosolproduction and combustion sources were found at several locations and a rangeof altitudes. At lower altitudes, particles with spectra resembling soil dustand biomass burning fingerprints were commonly observed. The types ofparticle spectra most commonly observed aloft were similar to those observedduring a previous study over the northwestern Pacific, indicating thatlong-range transport may have been an important particle source. Singleparticle spectra provided evidence that condensation and surface-limitedoxidation contributed to particle growth. Organic mass (OM) concentrationsranged from 1 to 7 μg m and averaged 2.4–4.1 μg m.Alkane functional groups were the largest fraction of OM, averaging1.9–2.1 μg m or 50–76% of OM, followed by alcoholfunctional groups (0.35–0.39 μg m, 9–14%). Organic andelemental concentrations are compared within and among geographical air massregions: "Pacific" free troposphere, "Continental" free troposphere,"Seattle" metropolitan region, and the California "Central Valley". OMconcentrations were highest and most variable in the Central Valley(3.5±2 μg m). Oxygen-to-carbon ratios were relativelyconstant in the Central Valley but variable for the Continental air masses.Overall, the OM concentrations showed greater variability within air masscategories as compared to averages among them, suggesting sampled air massregions included a variety of sources and processing of organic aerosol.