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Proc Natl Acad Sci U S A. 2018 May 15;115(20):5099-5104. doi: 10.1073/pnas.1801191115. Epub 2018 Apr 30.

Unexpected slowdown of US pollutant emission reduction in the past decade.

Author information

1
Atmospheric Chemistry Observations and Modeling Laboratory, National Center for Atmospheric Research, Boulder, CO 80301; zhejiang@ustc.edu.cn.
2
School of Earth and Space Sciences, University of Science and Technology of China, Hefei, Anhui, 230026, China.
3
Chemical Sciences Division, National Oceanic and Atmospheric Administration Earth System Research Laboratory, Boulder, CO 80305.
4
Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, Boulder, CO 80309.
5
Atmospheric Chemistry Observations and Modeling Laboratory, National Center for Atmospheric Research, Boulder, CO 80301.
6
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91009.
7
Research and Development Center for Global Change, Japan Agency for Marine-Earth Science and Technology, Yokohama, 236-0001, Japan.
8
Department of Mechanical Engineering, University of Colorado Boulder, Boulder, CO 80309.
9
Department of Physics, University of Toronto, Toronto, ON M5S 1A7, Canada.
10
Department of Hydrology and Atmospheric Sciences, University of Arizona, Tucson, AZ 85721.
11
Department of Atmospheric Science, Colorado State University, Fort Collins, CO 80523.
12
Department of Meteorological and Air Quality, Wageningen University, Wageningen, 6700, The Netherlands.
13
Satellite Observations Department, Royal Netherlands Meteorological Institute, De Bilt, 3731, The Netherlands.

Abstract

Ground and satellite observations show that air pollution regulations in the United States (US) have resulted in substantial reductions in emissions and corresponding improvements in air quality over the last several decades. However, large uncertainties remain in evaluating how recent regulations affect different emission sectors and pollutant trends. Here we show a significant slowdown in decreasing US emissions of nitrogen oxides (NO x ) and carbon monoxide (CO) for 2011-2015 using satellite and surface measurements. This observed slowdown in emission reductions is significantly different from the trend expected using US Environmental Protection Agency (EPA) bottom-up inventories and impedes compliance with local and federal agency air-quality goals. We find that the difference between observations and EPA's NO x emission estimates could be explained by: (i) growing relative contributions of industrial, area, and off-road sources, (ii) decreasing relative contributions of on-road gasoline, and (iii) slower than expected decreases in on-road diesel emissions.

KEYWORDS:

decadal scale variation; emission regulations; nitrogen oxides

PMID:
29712822
PMCID:
PMC5960319
DOI:
10.1073/pnas.1801191115
[Indexed for MEDLINE]
Free PMC Article

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