the Creative Commons Attribution 3.0 License.
the Creative Commons Attribution 3.0 License.
Inconsistent decadal variations between surface and free tropospheric nitrogen oxides over United States
Zhe Jiang
Helen Worden
John R. Worden
Daven K. Henze
Dylan B. A. Jones
Avelino F. Arellano
Emily V. Fischer
Liye Zhu
Kazuyuki Miyazaki
K. Folkert Boersma
Vivienne H. Payne
Abstract. Decreases in surface emissions of nitrogen oxides (NOx = NO + NO2) in North America have led to substantial improvements in air-quality over the last several decades. Here we show that satellite observations of tropospheric nitrogen dioxide (NO2) columns over the contiguous United States (US) do not decrease after about 2009, while surface NO2 concentrations continue to decline through to the present. This divergence, if it continues, could have a substantial impact on surface air quality due to mixing of free-tropospheric air into the boundary layer. Our results show only limited contributions from local effects such as fossil fuel emissions, lightning, or instrument artifacts, but we do find a possible relationship of NO2 changes to decadal climate variability. Our analysis demonstrates that the intensity of transpacific transport is stronger in El Niño years and weaker in La Niña years, and consequently, that decadal-scale climate variability impacts the contribution of Asian emissions on North American atmospheric composition. Because of the short lifetime, it is usually believed that the direct contribution of long-range transport to tropospheric NOx distribution is limited. If our hypothesis about transported Asian emissions is correct, then this observed divergence between satellite and surface NOx could indicate mechanisms that allow for either NOx or its reservoir species to have a larger than expected effect on North American tropospheric composition. These results therefore suggest more aircraft and satellite studies to determine the possible missing processes in our understanding of the long-range transport of tropospheric NOx.
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Zhe Jiang et al.
Interactive discussion


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RC1: 'Referee Comment', Anonymous Referee #2, 27 Jun 2017
Interactive discussion


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RC1: 'Referee Comment', Anonymous Referee #2, 27 Jun 2017
Zhe Jiang et al.
Zhe Jiang et al.
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