Halogen atoms and their oxides, termed reactive halogens, play a key role in atmospheric chemistry; being important oxidants that affect the lifetime of important trace gases and participating in the cycles which produce or destroy ozone. For example, tropospheric chlorine atoms are thought to contribute to a non-negligible portion of the removal of the greenhouse gas methane, and bromine monoxide is thought to play an important role in the oxidation of elemental mercury into a form that more readily deposits to ecosystems.
Chlorine monoxide may also contribute though that remains uncertain. The sources of tropospheric chlorine, bromine, and iodine atoms and oxides remain highly uncertain and poorly constrained. We have recently shown with measurements of ClNO2, a chlorine atom precursor formed by nighttime reactions of reactive nitrogen on aerosol particles, and analysis of aerosol and precipitation network data, that chlorine atom chemistry may be more widespread than currently predicted. We used the UWCM box model with a set of additional reactions to study the effects of chlorine atom chemistry and the multiphase chemistry of chlorine atom precursors on urban ozone production. This work was described in Riedel, et al ACP 2014. Click here to download the latest version of UWCM box model and the set of additional reactions used by Riedel et al. We have extended our measurement capabilities to include other halogen atom precursors (such as Cl2, Br2, BrCl, and HOCl). We plan to use our ion chemistry with a high-resolution time of flight mass spectrometer to make unambiguous assignments of our ion signal to halogen species by relying on their naturally occurring isotopic ratios. This work is currently funded through an NSF CAREER award.