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Published April 13, 2010 | Published + Supplemental Material
Journal Article Open

Response of an aerosol mass spectrometer to organonitrates and organosulfates and implications for atmospheric chemistry


Organonitrates (ON) are important products of gas-phase oxidation of volatile organic compounds in the troposphere; some models predict, and laboratory studies show, the formation of large, multifunctional ON with vapor pressures low enough to partition to the particle phase. Organosulfates (OS) have also been recently detected in secondary organic aerosol. Despite their potential importance, ON and OS remain a nearly unexplored aspect of atmospheric chemistry because few studies have quantified particulate ON or OS in ambient air. We report the response of a high-resolution time-of-flight aerosol mass spectrometer (AMS) to aerosol ON and OS standards and mixtures. We quantify the potentially substantial underestimation of organic aerosol O/C, commonly used as a metric for aging, and N/C. Most of the ON-nitrogen appears as NO_x^+ ions in the AMS, which are typically dominated by inorganic nitrate. Minor organonitrogen ions are observed although their identity and intensity vary between standards. We evaluate the potential for using NO_x^+ fragment ratios, organonitrogen ions, HNO_3^+ ions, the ammonium balance of the nominally inorganic ions, and comparison to ion-chromatography instruments to constrain the concentrations of ON for ambient datasets, and apply these techniques to a field study in Riverside, CA. OS manifests as separate organic and sulfate components in the AMS with minimal organosulfur fragments and little difference in fragmentation from inorganic sulfate. The low thermal stability of ON and OS likely causes similar detection difficulties for other aerosol mass spectrometers using vaporization and/or ionization techniques with similar or larger energy, which has likely led to an underappreciation of these species.

Additional Information

© 2010 by the National Academy of Sciences. Edited by Barbara J. Finlayson-Pitts, University of California, Irvine, CA, and approved January 29, 2010 (received for review October 25, 2009). Published online before print March 1, 2010. This study was funded by National Science Foundation Grants ATM 0449815 and 0650061, National Oceanic and Atmospheric Administration Grant NA08OAR4310565, and Department of Energy Biological and Environmental Research/Atmospheric Science Program Grant DEFG0208ER64627. We thank D. Eatough (Brigham Young University) for the ion chromatography data. We thank J. Kroll, B. Finlayson-Pitts, and two anonymous reviewers for useful suggestions. Author contributions: D.K.F. and J.L.J. designed research; D.K.F. and A.M. performed research; A.M., J.D.S., J.H.S., and P.J.Z. contributed new reagents/analytic tools; D.K.F., K.S.D., and J.L.J. analyzed data; and D.K.F. and J.L.J. wrote the paper.

Attached Files

Published - Farmer2010p9809P_Natl_Acad_Sci_Usa.pdf

Supplemental Material - pnas.0912340107_SI.pdf


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