Production, Emission, and Oxidation of Marine Trace Gases
Our research interests in this area are threefold. The first project focuses on the production of volatile organic compounds in the surface ocean, the second project focuses on chemical reactions occurring at the air-sea interface, and the third focuses on bacteria mediated production pathways for small molecules in the surface ocean.
Project A Overview: Volatile organic compounds (VOC) play a controlling role in both regulating oxidant loadings and setting the production rate of secondary organic aerosol (SOA) in both terrestrial and marine environments. To date, the vast majority of research has focused on terrestrial sources of VOC, with specific attention to the factors that control the emission rates of isoprene (C5H8), monoterpenes (C10H16), and sesquiterpenes (C15H24). In comparison, considerably less is known about marine VOC emissions (Shaw et al., 2010). Similar to terrestrial processes, the spatio-temporal distribution of marine VOC emissions is thought to be highly variable, depending on the number concentration and species of phytoplankton and/or bacteria. It has been suggested that marine VOC emissions in highly productive regions of the oceans: 1) impact oxidant loadings in the marine boundary layer (MBL), 2) contribute to SOA production, and 3) alter particle size and microphysical properties, thus impacting cloud formation and persistence in the MBL. At present, there exists an extreme paucity of experimental data of BVOC fluxes to constrain global models of ocean BVOC emissions and their subsequent impact on climate and atmospheric chemistry.
Project B Overview: The production rate of tropospheric ozone, depends critically on the concentrations of nitrogen oxides (NOx ≡ NO + NO2), volatile organic compounds (VOCs), trace oxidants (e.g., OH, NO3, and Cl) and the wavelength dependent actinic flux. Accurate model representation of O3 mixing ratios and the sensitivityof O3 to changes in NOx and VOC emissions rely heavily on a complete description of the factors that control NOx lifetimes and in turn the concentrations of atmospheric oxidants. Modeling studies, constrained by laboratory and field observations, suggest that nocturnal processes involving the nitrate radical (NO3) and N2O5, both products of NOx oxidation, can account for as much as 50% of the NOx removal rate (Alexander et al., 2009). Incorporation of the heterogeneous reaction of N2O5 on chloride containing aerosol particles (Finlayson-Pitts et al., 1989; Behnke et al., 1997) serves as both an efficient NOx recycling and halogen activation mechanism via the production of photo-labile nitryl chloride (ClNO2) in both coastal (Osthoff et al., 2008) and continental airmasses (Thornton et al., 2010). To date, study of the impact of nocturnal processes on the lifetime of NOx and the production of reactive halogen species in the marine boundary layer has concentrated on gas-phase reactions and heterogeneous and multiphase processes occurring on/within aerosol particles, with little attention paid to reactions occurring at the air-sea interface. This project focuses on direct measurements of the vertical flux of N2O5 and ClNO2 obtained via eddy covariance at a polluted coastal site to provide observation-based constraints on the role of the air-sea interface in setting the lifetime of reactive nitrogen and the production rate of reactive halogens in the marine boundary layer.
Project C Overview: Volatile organic compounds (VOC) play a controlling role in both regulating oxidant loadings and setting the production rate of secondary organic aerosol (SOA). To date, the vast majority of research has focused on terrestrial sources of VOC, while studies of marine VOC emissions have concentrated on a select few molecules (e.g., DMS, organic halides), and nearly exclusively on the role of phytoplankton in regulating their production rates. Here, we focus on the production of VOC and reduced nitrogen compounds (e.g., NH3) that are mediated by bacteria and or oxidation/photochemistry of DOM in the SML with the objective of determining production rates related to bacteria cell count and product yields for small organic molecules (e.g., aldehydes and ketones) formed following deposition of O3 to the SML.
Representative Publications:
Kim et al. A controlling role for the air-sea interface in the chemical processing of reactive nitrogen in the coastal marine boundary layer in PNAS 2014. Link to the article.
Kim et al. Air-Sea exchange of biogenic volatile organic compounds and the impact on aerosol particle size distributions in GRL 2017. Link to the article.
Novak and Bertram, Reactive VOC Production from Photochemical and Heterogeneous Reactions Occuring at the Air-Ocean Interface Accounts of Chemical Research 2020. Link to the article.
Group Members: Delaney Kilgour and Chris Jernigan
Funding Sources: NSF