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Using satellite observations of tropospheric NO_2 columns to infer long-term trends in US NO_x emissions: the importance of accounting for the free tropospheric NO_2 background

Silvern, Rachel F. and Jacob, Daniel J. and Mickley, Loretta J. and Sulprizio, Melissa P. and Travis, Katherine R. and Marais, Eloise A. and Cohen, Ronald C. and Laughner, Joshua L. and Choi, Sungyeon and Joiner, Joanna and Lamsal, Lok N. (2019) Using satellite observations of tropospheric NO_2 columns to infer long-term trends in US NO_x emissions: the importance of accounting for the free tropospheric NO_2 background. Atmospheric Chemistry and Physics, 19 (13). pp. 8863-8878. ISSN 1680-7324. https://resolver.caltech.edu/CaltechAUTHORS:20190801-084113348

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Abstract

The National Emission Inventory (NEI) of the US Environmental Protection Agency (EPA) reports a steady decrease in US NO_x emissions over the 2005–2017 period at a rate of 0.1 Tg N a^(−1) (53 % decrease over the period), reflecting sustained efforts to improve air quality. Tropospheric NO_2 columns observed by the satellite-based Ozone Monitoring Instrument (OMI) over the US show a steady decrease until 2009 but a flattening afterward, which has been attributed to a flattening of NO_x emissions, contradicting the NEI. We show here that the steady 2005–2017 decrease in NO_x emissions reported by the NEI is in fact largely consistent with observed network trends of surface NO_2 and ozone concentrations. The OMI NO_2 trend is instead similar to that observed for nitrate wet deposition fluxes, which is weaker than that for anthropogenic NO_x emissions, due to a large and increasing relative contribution of non-anthropogenic background sources of NO_x (mainly lightning and soils). This is confirmed by contrasting OMI NO_2 trends in urban winter, where the background is low and OMI NO_2 shows a 2005–2017 decrease consistent with the NEI, and rural summer, where the background is high and OMI NO_2 shows no significant 2005–2017 trend. A GEOS-Chem model simulation driven by NEI emission trends for the 2005–2017 period reproduces these different trends, except for the post-2009 flattening of OMI NO_2, which we attribute to a model underestimate of free tropospheric NO_2. Better understanding is needed of the factors controlling free tropospheric NO_2 in order to relate satellite observations of tropospheric NO_2 columns to the underlying NO_x emissions and their trends. Focusing on urban winter conditions in the satellite data minimizes the effect of this free tropospheric background.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.5194/acp-19-8863-2019DOIArticle
ORCID:
AuthorORCID
Silvern, Rachel F.0000-0002-6683-3238
Jacob, Daniel J.0000-0002-6373-3100
Mickley, Loretta J.0000-0002-7859-3470
Sulprizio, Melissa P.0000-0003-4641-5546
Travis, Katherine R.0000-0003-1628-0353
Marais, Eloise A.0000-0001-5477-8051
Cohen, Ronald C.0000-0001-6617-7691
Laughner, Joshua L.0000-0002-8599-4555
Choi, Sungyeon0000-0003-1608-343X
Joiner, Joanna0000-0003-4278-1020
Alternate Title:Using satellite observations of tropospheric NO2 columns to infer long-term trends in US NOx emissions: the importance of accounting for the free tropospheric NO2 background
Additional Information:© 2019 Author(s). This work is distributed under the Creative Commons Attribution 4.0 License. Published by Copernicus Publications on behalf of the European Geosciences Union. Received: 18 February 2019 – Discussion started: 25 February 2019. Revised: 24 May 2019 – Accepted: 3 June 2019 – Published: 12 July 2019. Author contributions: DJJ, LJM, and RFS designed the study. RFS and MPS conducted model simulations. RFS analyzed satellite, surface, and model data. KRT contributed NEI emissions in GEOS-Chem and supported data analysis. LJM, EAM, RCC, and JLL helped with scientific interpretation and discussion. SC, JJ, and LNL provided OMI data and supporting guidance. RFS and DJJ wrote the manuscript and all authors provided input on the paper for revision before submission. The authors declare that they have no conflict of interest. This study's contents are solely the responsibility of the grantee and do not necessarily represent the official views of the US EPA. Further, US EPA does not endorse the purchase of any commercial products or services mentioned in the publication. This research has been supported by the US Environmental Protection Agency (grant no. 83587201). Daniel J. Jacob was supported by the NASA Earth Science Division. Review statement: This paper was edited by Qiang Zhang and reviewed by two anonymous referees.
Funders:
Funding AgencyGrant Number
Environmental Protection Agency (EPA)83587201
NASAUNSPECIFIED
Issue or Number:13
Record Number:CaltechAUTHORS:20190801-084113348
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20190801-084113348
Official Citation:Silvern, R. F., Jacob, D. J., Mickley, L. J., Sulprizio, M. P., Travis, K. R., Marais, E. A., Cohen, R. C., Laughner, J. L., Choi, S., Joiner, J., and Lamsal, L. N.: Using satellite observations of tropospheric NO2 columns to infer long-term trends in US NOx emissions: the importance of accounting for the free tropospheric NO2 background, Atmos. Chem. Phys., 19, 8863-8878, https://doi.org/10.5194/acp-19-8863-2019, 2019
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:97573
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:01 Aug 2019 16:29
Last Modified:03 Oct 2019 21:32

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