Project No: 16218626

Title: Investigating inorganic iodine in Hong Kong, total loading, speciation, multiphase photochemistry, and impacts

Principal Investigator: Dr. Theodore K KOENIG

Co-Investigator: Prof. Zhe WANG

Abstract:

Atmospheric iodine is a major contributor to ozone destruction in the troposphere and to new particle formation and growth impacting human health and the radiative balance of Earth. Iodine is also a critical micronutrient whose availability is partly mediated by the atmosphere. Measurements of atmospheric iodine have generally focused on oxides which are active in photochemical ozone destruction and on oxoacids central to particle formation and growth. There have not been reports on atmospheric iodine levels in Hong Kong in over twenty years and the likely terrestrial sources of iodine indicated at the time remain unidentified. Recent years have seen major advances in our understanding of the atmospheric chemistry of iodine and revisions of its speciation and chemical mechanism. Preliminary investigations in Hong Kong have identified the consistent presence of several gaseous iodine species, possibly including some previously unreported in the atmosphere indicating understanding likely remains incomplete. A major gap in current understanding is that several lines of evidence indicate that particulate reservoirs of iodine are not stable and that there is extensive and active multiphase chemistry. However, the mechanism by which this occurs remains uncertain and so far there have been only limited investigations. We propose to employ online and offline techniques to measure total and speciated inorganic iodine in gas and particles. Aerosol Mass Spectrometry (AMS), Chemical Ionization Mass Spectrometry (CIMS) using nitrate (NO3) and bromide (Br) ions and a Volatilization Inlet for Aerosol (VIA), and Inductively Coupled Plasma Mass spectrometry (ICP-MS). Cross-sensitivity between species and phases will be checked in calibrations with an Aerosol Flow Tube (AFT). The AFT will further be used to investigate specific multiphase chemical reactions simultaneously monitoring iodine in both phases, with a particular focus on heterogenous reduction of iodate, understood to be the most stable reservoir. The AFT will also be used to investigate the chemical features and identity of the potentially novel species identified in existing ambient data. The same instruments will be used to collect ambient data in two coordinated campaigns and iteratively inform lab experiments. Ambient campaigns will also include a Long Path (LP) Differential Optical Absorption Spectroscopy (DOAS), to assess spatial homogeneity and connect with remote sensing data elsewhere. Measurements from both campaigns and experiments will be examined in chemical box models to update chemical mechanisms and to assess impacts on ozone, particulate matter, and human health; as well as global models to additionally examine transport of iodine.