Publication Date:
2017-09-19
Description:
Increasing free tropospheric ozone (O 3 ), combined with the high elevation and often deep boundary layers at western U.S. surface stations, poses challenges in attaining the more stringent 70 ppb O 3 National Ambient Air Quality Standard. As such, use of observational data to identify sources and mechanisms that contribute to surface O 3 is increasingly important. This work analyzes surface and vertical O 3 observations over California and Nevada from 1995 to 2015. Over this period, the number of high O 3 events (95th percentile) at the U.S. Environmental Protection Agency Clean Air Status and Trends Network (CASTNET) sites has decreased during summer, as a result of decreasing U.S. emissions. In contrast, an increase in springtime 5th percentile O 3 indicates a general increase of baseline O 3 . During 2012 there was a peak in exceedances and in the average spring-summer O 3 mixing ratios at CASTNET sites. Goddard Earth Observing System-Chem results show that the surface O 3 attributable to transport from the upper troposphere and stratosphere was increased in 2013 compared to 2012, highlighting the importance of measurements aloft. Vertical O 3 measurements from aircraft, ozonesondes, and lidar show distinct seasonal trends, with a high percentage of elevated O 3 laminae (O 3 〉 70 ppb, 3–8 km) during spring and summer. Analysis of the timing of high O 3 surface events and correlation between surface and vertical O 3 data is used to discuss varying sources of western U.S. surface O 3 . Published 2017. This article is a U.S. Government work and is in the public domain in the USA.
Print ISSN:
2169-897X
Electronic ISSN:
2169-8996
Topics:
Geosciences
,
Physics
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