Dominance of atypical oxidant sources in the polluted wintertime boundary layer: insights from the WINTER C-130 aircraft campaign
Abstract
As part of the Wintertime Investigation of Transport, Emissions, and Reactivity (WINTER) campaign in February - March 2015, a suite of measurements were made across the northeastern U.S. aboard the NSF/NCAR C-130 aircraft to constrain the abundance and distribution of oxidant sources, including O3, HCHO, HONO, ClNO2, and Cl2. These observations together with models of daily photolysis rates are used to assess the horizontal and vertical contributions to the primary daytime oxidant source over polluted continental regions and in the marine boundary layer (MBL) during winter. In the marine boundary layer, the observations suggest that ClNO2 represents 30 - 80% of the total integrated daytime primary radical source, often dominating the OH source from O3 photolysis to O1D, and routinely competing with HCHO. HONO was typically less than 10% of the primary oxidant source in the MBL neglecting daytime formation. In the near surface layer over land, HONO was often 20 - 30% of the primary oxidant source, scaling with urban NOx sources, but its contribution in the vertical was variable and often its importance was uncertain due to instrument detection limits near 20 pptv. ClNO2 was almost always less than 15% of the daily oxidant source in the inland continental boundary layer. HCHO and O3 photolysis were generally comparable, each accounting for 30 - 50% of the oxidant source on average in both regions. In the continental boundary layer, HCHO was almost always more important as a primary oxidant source than that from O3 photolysis. Sources of HCHO in the wintertime boundary layer remain uncertain, but HCHO concentrations were often correlated with carbon monoxide, and together with the lack of significant biogenic VOC emissions, suggests anthropogenic sources dominate. We discuss the important contribution of regional anthropogenic emissions to the oxidative capacity of wintertime polluted regions via ClNO2, HONO, and HCHO.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFM.A42A..01T
- Keywords:
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- 0317 Chemical kinetic and photochemical properties;
- ATMOSPHERIC COMPOSITION AND STRUCTUREDE: 0365 Troposphere: composition and chemistry;
- ATMOSPHERIC COMPOSITION AND STRUCTUREDE: 0368 Troposphere: constituent transport and chemistry;
- ATMOSPHERIC COMPOSITION AND STRUCTUREDE: 3305 Climate change and variability;
- ATMOSPHERIC PROCESSES