Laboratory Measurements And Modeling Of Trace Atmospheric Species

Author : Gordon Novak
Publisher :
ISBN 13 :
Total Pages : 257 pages
Book Rating : 4.:/5 (126 download)

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Download or read book Water Interfaces as a Source and Sink of Reactive Trace Gases in the Atmosphere written by Gordon Novak and published by . This book was released on 2020 with total page 257 pages. Available in PDF, EPUB and Kindle. Book excerpt: The ocean surface serves as a source and sink for a diverse set of reactive trace gases in the atmosphere, including volatile organic compounds (VOC), reactive halogens, and oxidized and reduced nitrogen compounds. The exchange of reactive trace gases between the atmosphere and ocean has been shown to alter atmospheric oxidant concentrations and drive particle nucleation and growth. Uncertainties in cloud radiative forcing and aerosol-cloud interactions are among the largest uncertainties in current global climate models. Climate models are particularly sensitive to cloud cover over the remote ocean due to large changes in albedo between the ocean surface and cloud tops. Oceanic emissions contribute to cloud condensation nuclei concentrations, either through the direct emission of particles during wave breaking, or through the formation of secondary aerosol particles following the emission of reactive gas-phase compounds. Despite generally small and diffuse oceanic emission rates for reactive trace gases, it has been shown that oxidant and particle number concentrations are acutely sensitive to air-sea trace gas exchange rates and the chemical composition of emitted species. To date, field measurements of air-sea reactive gas exchange have focused primarily on the emission of gases of biological origin, such as dimethyl sulfide (DMS). While DMS emissions are relatively well constrained, the gas-phase oxidation that connects DMS to sulfate aerosol is less well understood. Recent laboratory measurements suggest that heterogeneous and photochemical reactions occurring at the air-sea interface can also lead to the production and emission of a wide array of reactive VOC. When laboratory-based measurements are used to derive global scale emissions, the calculated sea-to-air fluxes of reactive VOC generated from heterogeneous and photochemical processes are comparable or larger in magnitude to the sea-to-air flux of DMS. It is not yet clear how the mechanisms proposed in these laboratory experiments translate to atmospheric conditions. The proposed abiotic emissions are also a potential source of VOC in regions of low biological activity which carries important implications for regional and global modeling. This thesis presents work to directly constrain the magnitude and speciation of biotic and abiotic ocean-atmosphere VOC exchange and subsequent processing in the atmosphere. Chapter 1 details direct eddy covariance flux measurements of O3 deposition to the coastal ocean from a deployment to Scripps Pier La Jolla, CA in 2018. The rate of O3 deposition to the ocean is important as both a sink of O3 which is an air pollutant and greenhouse gas, and also because it controls the magnitude of potential abiotic emissions from heterogeneous chemistry at the ocean atmosphere interface. Chapter 2 presents the first broad survey of VOC air-sea exchange by eddy covariance flux at the coastal Scripps Pier site. This study directly targeted biotic and abiotic VOC emission fluxes and included coincident measurements of solar irradiance, O3 mixing ratios, and ocean biochemical parameters. In Chapter 3 I describe the use of eddy covariance flux measurements from an airborne platform on the NASA Atmospheric Tomography mission (ATom) as a probe of cloud processing and uptake in the marine boundary layer. Cloud uptake can act as a terminal sink of low volatility species in the boundary layer, affecting VOC, HOx, and NOx budgets in cloud capped boundary layers. Chapters 4 and 5 describe the characterization of new chemical ionization mass spectrometry methods which enable the high sensitivity and precision measurements necessary for the eddy covariance technique. Chapter 4 presents detailed calibrations of benzene cluster cation reagent ions for the detection of isoprene, monoterpenes, and sesquiterpenes. Chapter 5 is a detailed characterization of oxygen anion reagent ion chemistry (Ox-CIMS) which enables extremely high sensitivity detection of O3 necessary for measurements of O3 deposition to the ocean. Together this thesis describes new tools for and new observations of the air-sea exchange of reactive trace gases.