HR: 0800h
AN: A11A-0843    [Abstracts]
TI: Photochemical Production of Alkyl Nitrates in the Tropical Pacific Ocean
AU: * Dahl, E E
EM: edahl@esf.edu
AF: Department of Earth System Science, University of California at Irvine, 1212 Croul Hall, Irvine, CA 92697 United States
AU: Yvon-Lewis, S A
EM: syvon-lewis@ocean.tamu.edu
AF: Department of Oceanography, Texas A&M University, 3146 TAMU, College Station, TX 77843 United States
AU: Saltzman, E S
EM: esaltzma@uci.edu
AF: Department of Earth System Science, University of California at Irvine, 1212 Croul Hall, Irvine, CA 92697 United States
AB: Alkyl nitrates are important to the tropospheric NOx/ozone cycle because they represent a significant fraction of the reactive nitrogen (NOy). Previous work has shown that there is an oceanic source of alkyl nitrates. A photochemical mechanism for the formation of alkyl nitrates in seawater has been proposed. This mechanism involves the reaction of ROO and NO, where ROO is an alkyl peroxy radical. ROO and NO radicals in seawater are derived from the photolysis of DOM and nitrite, respectively. In this study, the photochemical production of low molecular weight alkyl nitrates (C1-C3) was observed in shipboard incubation experiments in the tropical Pacific during the PHASE 1 cruise. Seawater samples from several regions, including high and low-chlorophyll areas, were collected and incubated. Alkyl nitrate production rates as high as 2 nM/hour were observed. The production rate of alkyl nitrates was clearly dependent upon the initial concentration of nitrite, most likely as the source for NO radicals. While the magnitude of production varied between sample locations, the ratios of the production rates of the various alkyl nitrates remained relatively constant. The observed production ratios of methyl, ethyl, isopropyl, and n-propyl nitrate were 5.9:1.0:0.1:0.2. These ratios presumably reflect the speciation of peroxy radicals formed in seawater, and the yield of alkyl nitrates from the ROO+NO reaction. The observed production rate ratios are similar to the concentration ratios of alkyl nitrates observed in ambient seawater and the overlying atmosphere during the study. A comparison of the measured production rates and the observed concentrations, suggests that photochemically produced alkyl nitrates are a major source of atmospheric alkyl nitrates in the surface ocean and marine atmosphere.
DE: 0312 Air/sea constituent fluxes (3339, 4504)
DE: 0315 Biosphere/atmosphere interactions (0426, 1610)
DE: 0469 Nitrogen cycling
DE: 4820 Gases
DE: 4852 Photochemistry
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005