Ion chemistry of ClONO2 involving NO3− core ions: A detection scheme for ClONO2 in the atmosphere

Abstract

Rate constants and product branching ratios for reactions involving atmospherically interesting ions and ClONO2 have been measured. H3O+ reacts rapidly with ClONO2, but hydrates of H3O+ do not. This implies that ClONO2 does not play a central role in the positive ion chemistry of the atmosphere. CO3− reacts with ClONO2 to form NO3−. Both NO3− and NO3− (H2O) react with ClONO2 to form NO3− (ClONO2). H2O does not react with NO3− (ClONO2), which is essential to the proposed in situ measurement technique. NO3− (ClONO2) does react with HNO3 and HCl, producing NO3− (HNO3) in both cases. The reaction of NO3− (HCl) with ClONO2 also produces NO3− (HNO3). These latter two efficient reactions, which are discussed in detail in a separate publication, are analogous to the efficient neutral heterogeneous reaction of HCl with ClONO2 which is important in the chemistry of the Antarctic stratosphere. A detection scheme is presented for atmospheric ClONO2 based on the reactions studied and utilizing mass spectrometry. A ClONO2 detection limit of 107 molecules cm−3 is estimated based on the operating characteristics of current ion‐molecule based mass spectrometric field instruments.