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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/acp-2016-1100
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
02 Jan 2017
Review status
A revision of this discussion paper was accepted for the journal Atmospheric Chemistry and Physics (ACP) and is expected to appear here in due course.
Global deposition of total reactive nitrogen oxides from 1996 to 2014 constrained with satellite observations of NO2 columns
Jeffrey A. Geddes1,a and Randall V. Martin2 1Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia, Canada
2Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts, USA
amow at: Department of Earth and Environment, Boston University, Boston, Massachusetts, USA
Abstract. Reactive nitrogen oxides (NOy) are a major constituent of the nitrogen deposited from the atmosphere, but observational constraints on their deposition are limited by poor or nonexistent measurement coverage in many parts of the world. Here we apply NO2 observations from multiple satellite instruments (GOME, SCIAMACHY, and GOME-2) to constrain the global deposition of NOy over the last two decades. We accomplish this by producing top-down estimates of NOx emissions from inverse modeling of satellite NO2 columns over 1996–2014, and including these emissions in the GEOS-Chem chemical transport model to simulate chemistry, transport, and deposition of NOy. Our estimates of long-term mean wet nitrate (NO3) deposition are highly consistent with available measurements in North America, Europe, and East Asia combined (r = 0.83, normalized mean bias = −7 %, N = 136). Likewise, our calculated trends in wet NO3 deposition are largely consistent with the measurements, with 129 of the 136 gridded model-data pairs sharing overlapping 95 % confidence intervals. We find that global mean NOy deposition over 1996–2014 is 56.0 Tg N yr−1, with a minimum in 2006 of 50.5 Tg N and a maximum in 2012 of 60.8 Tg N. Regional trends are large, with opposing signs in different parts of the world. Over 1996 to 2014, NOy deposition decreased by up to 60 % in eastern North America, doubled in regions of East Asia, and declined by 20 % in parts of Western Europe. About 40 % of the global NOy deposition occurs over oceans, with deposition to the North Atlantic Ocean declining and deposition to the northwestern Pacific Ocean increasing. Using the residual between NOx emissions and NOy deposition over specific land regions, we investigate how NOx export via atmospheric transport has changed over the last two decades. Net export from the continental United States decreased substantially, from 2.9 Tg N yr−1 in 1996 to 1.5 Tg N yr−1 in 2014. On the other hand, export from China more than tripled between 1996 and 2011 (from 1.0 Tg N yr−1 to 3.5 Tg N yr−1), before a striking decline to 2.5 Tg N yr−1 by 2014. We find that declines in NOx export from some Western European countries have counteracted increases in emissions from neighbouring countries to the east. A sensitivity study indicates that simulated NOy deposition is robust to uncertainties in NH3 emissions with a few exceptions. Our novel long-term study provides timely context on the rapid redistribution of atmospheric nitrogen transport and subsequent deposition to ecosystems around the world.

Citation: Geddes, J. A. and Martin, R. V.: Global deposition of total reactive nitrogen oxides from 1996 to 2014 constrained with satellite observations of NO2 columns, Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2016-1100, in review, 2017.
Jeffrey A. Geddes and Randall V. Martin
Jeffrey A. Geddes and Randall V. Martin

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Short summary
Here we apply NO2 observations from multiple satellite records with the help of a chemical transport model to constrain the global deposition of reactive nitrogen oxides (NOy) over the last two decades. NOy deposition decreased by up to 60 % in eastern North America, doubled in regions of East Asia, and declined by 20 % in parts of Western Europe. We also find changes in the export of NOy via atmospheric transport, with direct impacts on countries downwind of source regions.
Here we apply NO2 observations from multiple satellite records with the help of a chemical...
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