Elemental analysis of aerosol organic nitrates with electron ionization high-resolution mass spectrometry

Abstract. Four hydroxynitrates (R(OH)R'ONO₂) representative of atmospheric volatile organic compound (VOC) oxidation products were synthesized, nebulized and sampled into an Aerodyne High Resolution Time of Flight Aerosol Mass Spectrometer (HR-ToF-AMS). The resulting mass spectrum was used to evaluate calibration factors for elemental analysis of organic nitrates by AMS, and to determine the distribution of nitrogen in the detected fragments in a search for an AMS signature of organic nitrates. We found that 30% of the detected nitrogen mass is in the NO⁺ and NO₂⁺ fragments, 12% at NH_x⁺ fragments, 5% at C_xH_yO_zN⁺ fragments, and 53% at various C_xH_yN⁺ fragments. Elemental analysis indicated that nitrogen was detected with higher efficiency than carbon and hydrogen, but oxygen was detected with reduced efficiency compared to previously reported results for a suite of organics which did not include organic nitrates. The results are used to suggest the maximum corrections to ambient O:C and N:C ratios based on AMS measurements.