Chemical signatures for sources and reactions of organic atmospheric aerosols.

摘要

Two new analysis procedures have been developed for the classification of atmospheric aerosol-phase organic compounds, adding to the current understanding of aerosol composition, solubility, and reaction mechanisms. The first utilizes Fourier Transform Infra-Red (FTIR) spectroscopy to measure the organic and inorganic functional group composition of submicron aerosol samples on Teflon filters. A four-solvent rinsing procedure separates these functional groups into solubility fractions, providing some of the first simultaneous information about the water-soluble and insoluble organic carbon in atmospheric aerosol particles. The second procedure uses scanning transmission X-ray microscopy (STXM) to measure spatial distributions of carbon, potassium, calcium, oxygen, and nitrogen functional groups with a resolution of better than 0.1 mum. STXM is the first technique to measure the mixing state of organic functional groups within individual aerosol particles.; Aircraft-based FTIR measurements of submicron aerosol in the Caribbean identified fractional water soluble organic carbon (WSOC) compositions that increased with altitude. These measurements, combined with STXM, were the first to identify internally-mixed WSOC in dust aerosol from Saharan Africa. Near Japan, FTIR and thermal-optical transmittance (TOT) measurements of organic carbon (OC) were related with a slope of 0.91 and an R2 value of 0.93, suggesting that the techniques quantify very similar groups of species as OC. TOT relies on an estimated ratio for conversion of OC to organic mass, and FTIR provided the first calculations of this ratio that were based on a majority of the TOT-measured OC. FTIR measurements during three New Jersey rain events provided the first evidence that water-soluble functional groups are scavenged more efficiently than hydrophobic species. STXM measurements of Caribbean, Asian, and U.S. aerosol samples revealed organic compositions that varied as functions of particle size. A novel technique for relating this size-dependence to atmospheric oxidation and condensation processes was used to determine organic aerosol oxidative conversion rates ranging from 13--24% of organic mass per day. These rate measurements, the first based on atmospheric aerosol particles, are a factor of three lower than those typically used in climate models.