Ultrahigh-resolution FT-ICR mass spectrometry characterization of α-pinene ozonolysis SOA

Secondary organic aerosol (SOA) of alpha-pinene ozonolysis with and without hydroxyl radical scavenging hexane was characterized by ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Molecular formulas for more than 900 negative ions were identified over the mass range of 100-850 u. Hydroxyl radicals formed during the ozonolysis of alpha-pinene might be expected to alter the composition of SOA, however a majority of the molecular formulas were identified in all three experiments and with a few exceptions they had similar relative abundances. Thus, the detailed composition of SOA was only slightly influenced by the presence or absence of hydroxyl radical scavenging hexane. The negative-ion mass spectra of the SOA contained four groups of peaks with increasing mass spectral complexity corresponding to increasing molecular weight. The mean values of 0:C decreased from 0.55 to 0.42 with increasing molecular weight, but the mean value of H:C, approximately 1.5, did not change with increasing molecular weight. The molecular formulas with the highest relative abundances in Groups I and II contained 5-7 and 7-10 oxygen atoms and 3-4 and 5-7 double bond equivalents, respectively. The molecular formulas with the highest relative abundances in Groups III and IV contained 10-13 and 13-16 oxygen atoms and 7-9 and 9-11 double bond equivalents, respectively. Observations of the oxygen content and the double bond equivalents of the SOA products suggest a complex mixture of accretion reaction mechanisms, without an easily confirmable dominating pathway. (C) 2011 Elsevier Ltd. All rights reserved.