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An Assessment of Ground Level and Free Tropospheric Ozone Over California and Nevada
Author(s) -
Yates E. L.,
Johnson M. S.,
Iraci L. T.,
Ryoo J.M.,
Pierce R. B.,
Cullis P. D.,
Gore W.,
Ives M. A.,
Johnson B. J.,
Leblanc T.,
Marrero J. E.,
Sterling C. W.,
Tanaka T.
Publication year - 2017
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1002/2016jd026266
Subject(s) - troposphere , environmental science , ozone , tropospheric ozone , atmospheric sciences , ground level ozone , percentile , climatology , lidar , meteorology , geography , geology , statistics , remote sensing , mathematics
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 .