Bulk Organic Aerosol Analysis by Proton-Transfer-Reaction Mass Spectrometry: An Improved Methodology for the Determination of Total Organic Mass, O:C and H:C Elemental Ratios, and the Average Molecular Formula

We have recently shown in this journal (Müller et al. Anal. Chem. 2017 , 89 , 10889 - 10897 ) how a proton-transfer-reaction mass spectrometry (PTR-MS) analyzer measured particulate organic matter in urban atmospheres using the " Ch emical A nalysis of Ae r osol On line" (CHARON) inlet. Our initial CHARON studies did not take into account fragmentation of protonated analyte molecules, which introduced a small but significant negative bias in the determination of bulk organic aerosol parameters. Herein, we studied the ionic fragmentation of 26 oxidized organic compounds typically found in atmospheric particles. This allowed us to derive a correction algorithm for the determination of the bulk organic mass concentration, m OA , the bulk-average hydrogen-to-carbon ratio, (H:C) bulk , the bulk-average oxygen-to-carbon ratio, (O:C) bulk , and the bulk-average molecular formula, MF bulk . The correction algorithm was validated against AMS data using two sets of published data. Finally, we determined MF bulk of particles generated from the reaction of α-pinene and ozone and compared and discussed the results in relation to the literature.