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Nature. 2016 Apr 28;532(7600):489-91. doi: 10.1038/nature17195. Epub 2016 Apr 11.

Rapid cycling of reactive nitrogen in the marine boundary layer.

Author information

1
Wadsworth Center, New York State Department of Health, Albany, New York, USA.
2
Department of Environmental Health Sciences, State University of New York, Albany, New York, USA.
3
Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles (UCLA), California, USA.
4
Department of Atmospheric and Oceanic Sciences, University of Colorado at Boulder, Boulder, Colorado, USA.
5
Department of Physics, University of Helsinki, Helsinki, Finland.
6
National Center for Atmospheric Research, Boulder, Colorado, USA.
7
Pacific Northwest National Laboratory, Richland, Washington, USA.
8
NOAA, Earth System Research Laboratory, Chemical Sciences Division, Boulder, Colorado, USA.
9
Cooperative Institute for Research in Environmental Sciences, University of Colorado at Boulder, Boulder, Colorado, USA.
10
Institute for Meteorology and Geophysics, University of Innsbruck, Innsbruck, Austria.
11
University of Eastern Finland, Kuopio, Finland.

Abstract

Nitrogen oxides are essential for the formation of secondary atmospheric aerosols and of atmospheric oxidants such as ozone and the hydroxyl radical, which controls the self-cleansing capacity of the atmosphere. Nitric acid, a major oxidation product of nitrogen oxides, has traditionally been considered to be a permanent sink of nitrogen oxides. However, model studies predict higher ratios of nitric acid to nitrogen oxides in the troposphere than are observed. A 'renoxification' process that recycles nitric acid into nitrogen oxides has been proposed to reconcile observations with model studies, but the mechanisms responsible for this process remain uncertain. Here we present data from an aircraft measurement campaign over the North Atlantic Ocean and find evidence for rapid recycling of nitric acid to nitrous acid and nitrogen oxides in the clean marine boundary layer via particulate nitrate photolysis. Laboratory experiments further demonstrate the photolysis of particulate nitrate collected on filters at a rate more than two orders of magnitude greater than that of gaseous nitric acid, with nitrous acid as the main product. Box model calculations based on the Master Chemical Mechanism suggest that particulate nitrate photolysis mainly sustains the observed levels of nitrous acid and nitrogen oxides at midday under typical marine boundary layer conditions. Given that oceans account for more than 70 per cent of Earth's surface, we propose that particulate nitrate photolysis could be a substantial tropospheric nitrogen oxide source. Recycling of nitrogen oxides in remote oceanic regions with minimal direct nitrogen oxide emissions could increase the formation of tropospheric oxidants and secondary atmospheric aerosols on a global scale.

PMID:
27064904
DOI:
10.1038/nature17195
[Indexed for MEDLINE]

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