摘要:

The chemical composition of secondary organic aerosol (SOA) particles, formed by the dark ozonolysis of alpha-pinene, was characterized by a high-resolution time-of-flight aerosol mass spectrometer. The experiments were conducted using a continuous-flow chamber, allowing the particle mass loading and chemical composition to be maintained for several days. The organic portion of the particle mass loading was varied from 0.5 to >140 mu g/m(3) by adjusting the concentration of reacted alpha-pinene from 0.9 to 91.1 ppbv. The mass spectra of the organic material changed with loading. For loadings below 5 mu g/m(3) the unit-mass-resolution m/z 44 (CO2+) signal intensity exceeded that of m/z 43 ( predominantly C2H3O+), suggesting more oxygenated organic material at lower loadings. The composition varied more for lower loadings (0.5 to 15 mu g/m(3)) compared to higher loadings (15 to >140 mu g/m(3)). The high-resolution mass spectra showed that from >140 to 0.5 mu g/m(3) the mass percentage of fragments containing carbon and oxygen (CxHyOz+) monotonically increased from 48% to 54%. Correspondingly, the mass percentage of fragments representing CxHy+ decreased from 52% to 46%, and the atomic oxygen-to-carbon ratio increased from 0.29 to 0.45. The atomic ratios were accurately parameterized by a four-product basis set of decadal volatility (viz. 0.1, 1.0, 10, 100 mu g/m(3)) employing products having empirical formulas of C1H1.32O0.48, C1H1.36O0.39, C1H1.57O0.24, and C1H1.76O0.14. These findings suggest considerable caution is warranted in the extrapolation of laboratory results that were obtained under conditions of relatively high loading (i.e., >15 mu g/m(3)) to modeling applications relevant to the atmosphere, for which loadings of 0.1 to 20 mu g/m(3) are typical. For the lowest loadings, the particle mass spectra resembled observations reported in the literature for some atmospheric particles.

附注:

ISI Document Delivery No.: 406WPTimes Cited: 24Cited Reference Count: 55Shilling, J. E. Chen, Q. King, S. M. Rosenoern, T. Kroll, J. H. Worsnop, D. R. DeCarlo, P. F. Aiken, A. C. Sueper, D. Jimenez, J. L. Martin, S. T.National Science Foundation [ATM-0513463]; NSF [ATM-0449815]; EPA [STAR-RD-83216101-0]; EPA STAR fellowship ; Danish Agency for Science Technology and Innovation [272-06-0318]; NASA ESS fellowshipThis material is based upon work supported by the National Science Foundation under Grant No. ATM-0513463. The development of the method for quantifying O/C and H/C was supported by NSF grant ATM-0449815 and EPA grant STAR-RD-83216101-0. SMK and PFD acknowledge support from the EPA STAR fellowship program. TR acknowledges support from the Danish Agency for Science Technology and Innovation under Grant No. 272-06-0318. QC and ACA acknowledge support from the NASA ESS fellowship program. This paper has not been reviewed by any funding agency and thus any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of a funding agency.Copernicus publicationsKathlenburg-lindau