Regional differences in organic composition of submicron and single particles during INTEX-B 2006

Organic functional group and elemental concentrations were measured with Fourier transform infrared (FTIR) spectroscopy and X-ray fluorescence (XRF) from an aircraft platform as part of the Intercontinental Chemical Transport Experiment – Phase B (INTEX-B) conducted over the eastern Pacific and western North America. Single particle spectra were obtained using scanning transmission X-ray microscopy-near edge X-ray absorption fine structure spectrometry (STXM-NEXAFS). Organic mass (OM) concentrations ranged from 1 to 7 μg m−3 and averaged 2.4-4.1 μg m−3. Alkane functional groups were the largest fraction of OM, averaging 1.9-2.1 μg m−3 or 50-76% of OM. Alcohol functional groups comprised the second largest fraction of OM (0.350.39 μg m−3, 9-14%). Organic and elemental concentrations are compared within and among geographical air mass regions: “Pacific” free troposphere, “Continental” free troposphere, “Seattle” metropolitan region, and the California “Central Valley”. OM concentrations were highest and most variable in the Central Valley (3.5±2 μg m−3). Alcohol functional group concentrations were highest in the Continental and Central Valley and lowest in the Pacific and Seattle air masses. Oxygen-to-carbon ratios were relatively constant in the Central Valley but variable for the Continental air masses. Most elemental concentrations did not show large variations among or within air mass categories. Overall, the OM concentrations showed greater variability within air mass categories as compared to averages among them, suggesting sampled air mass regions included a variety of sources, processing, and losses of organic aerosol. Single particle spectra obtained by STXM-NEXAFS were classified into metaclasses associated with different sources and atmospheric processing. Particles with spectra indicative of secondary organic aerosol production and combustion sources were found at several locations and a range of altitudes. At lower altitudes, particles with spectra resembling soil dust and biomass burning fingerprints were commonly observed. Single particle spectra provided evidence that condensation and surface-limited oxidation contributed to particle growth.