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Volume 18, issue 15
Atmos. Chem. Phys., 18, 11185-11203, 2018
https://doi.org/10.5194/acp-18-11185-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Atmos. Chem. Phys., 18, 11185-11203, 2018
https://doi.org/10.5194/acp-18-11185-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 10 Aug 2018

Research article | 10 Aug 2018

Global impact of nitrate photolysis in sea-salt aerosol on NOx, OH, and O3 in the marine boundary layer

Prasad Kasibhatla1, Tomás Sherwen2,3, Mathew J. Evans2,3, Lucy J. Carpenter2, Chris Reed2,4, Becky Alexander5, Qianjie Chen5, Melissa P. Sulprizio6, James D. Lee2, Katie A. Read2, William Bloss7, Leigh R. Crilley7, William C. Keene8, Alexander A. P. Pszenny9, and Alma Hodzic10,11 Prasad Kasibhatla et al.
  • 1Nicholas School of the Environment, Duke University, Durham, NC 27708, USA
  • 2Wolfson Atmospheric Chemistry Laboratories, Department of Chemistry, University of York, York YO10 5DD, UK
  • 3National Centre for Atmospheric Science, University of York, York YO10 5DD, UK
  • 4Facility for Airborne Atmospheric Measurements (FAAM), Cranfield University, Cranfield, MK43 0AL, UK
  • 5Department of Atmospheric Sciences, University of Washington, Seattle, WA 98195, USA
  • 6John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA
  • 7School of Geography, Earth and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK
  • 8Department of Environmental Sciences, University of Virginia, Charlottesville, VA 22904, USA
  • 9Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, NH 03824, USA
  • 10National Center for Atmospheric Research, Boulder, CO 80305, USA
  • 11Laboratoire d'Aérologie, Université de Toulouse, CNRS, Paul Sabatier University, France

Abstract. Recent field studies have suggested that sea-salt particulate nitrate (NITs) photolysis may act as a significant local source of nitrogen oxides (NOx) over oceans. We present a study of the global impact of this process on oxidant concentrations in the marine boundary layer (MBL) using the GEOS-Chem model, after first updating the model to better simulate observed gas–particle phase partitioning of nitrate in the marine boundary layer. Model comparisons with long-term measurements of NOx from the Cape Verde Atmospheric Observatory (CVAO) in the eastern tropical North Atlantic provide support for an in situ source of NOx from NITs photolysis, with NITs photolysis coefficients about 25–50 times larger than corresponding HNO3 photolysis coefficients. Short-term measurements of nitrous acid (HONO) at this location show a clear daytime peak, with average peak mixing ratios ranging from 3 to 6 pptv. The model reproduces the general shape of the diurnal HONO profile only when NITs photolysis is included, but the magnitude of the daytime peak mixing ratio is under-predicted. This under-prediction is somewhat reduced if HONO yields from NITs photolysis are assumed to be close to unity. The combined NOx and HONO analysis suggests that the upper limit of the ratio of NITs : HNO3 photolysis coefficients is about 100. The largest simulated relative impact of NITs photolysis is in the tropical and subtropical marine boundary layer, with peak local enhancements ranging from factors of 5 to 20 for NOx, 1.2 to 1.6 for OH, and 1.1 to 1.3 for ozone. Since the spatial extent of the sea-salt aerosol (SSA) impact is limited, global impacts on NOx, ozone, and OH mass burdens are small ( ∼ 1–3 %). We also present preliminary analysis showing that particulate nitrate photolysis in accumulation-mode aerosols (predominantly over continental regions) could lead to ppbv-level increases in ozone in the continental boundary layer. Our results highlight the need for more comprehensive long-term measurements of NOx, and related species like HONO and sea-salt particulate nitrate, to better constrain the impact of particulate nitrate photolysis on marine boundary layer oxidant chemistry. Further field and laboratory studies on particulate nitrate photolysis in other aerosol types are also needed to better understand the impact of this process on continental boundary layer oxidant chemistry.

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Recent measurements of NOx and HONO suggest that photolysis of particulate nitrate in sea-salt aerosols is important in terms of marine boundary layer oxidant chemistry. We present the first global-scale assessment of the significance of this new chemical pathway for NOx, O3, and OH in the marine boundary layer. We also present a preliminary assessment of the potential impact of photolysis of particulate nitrate associated with other aerosol types on continental boundary layer chemistry.
Recent measurements of NOx and HONO suggest that photolysis of particulate nitrate in sea-salt...
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