Impact of transported background ozone inflow on summertime air quality in a California ozone exceedance area D. D. Parrish1, K. C. Aikin1,2, S. J. Oltmans3, B. J. Johnson3, M. Ives4, and C. Sweeny3 1NOAA ESRL Chemical Sciences Division, 325 Broadway, Boulder, CO 80305, USA 2CIRES, University of Colorado, Boulder, CO 80309, USA 3NOAA ESRL Global Monitoring Division, 325 Broadway, Boulder, CO 80305, USA 4Humboldt State Marine Lab, 570 Ewing St., Trinidad Head, CA, 95570, USA
Abstract. Ozone sondes launched from Trinidad Head, California provide a measure of
background O3 transported ashore, and allow an evaluation of the impact
of this transport on air quality in California's Northern Sacramento Valley.
A strong summertime vertical O3 gradient and correlation analysis
indicate that O3-rich air from above the marine boundary layer is
transported to the surface. Surface O3 is found to increase
proportionally to the transported background. At the surface site
experiencing the highest O3 concentrations, the mean maximum daily 8-h
average (MDA8) O3 on exceedance days (i.e. those days when MDA8 O3
exceeds 75 ppbv) is 20 ppbv higher than on non-exceedance days. The
transported background O3, as measured 22 h earlier by the Trinidad
Head sondes, accounts for more than half (11 ppbv) of this difference. This
finding contrasts with conclusions from model calculations that indicate the
US policy relevant O3 background is generally 15–35 ppbv, and that it
is lower, rather than higher, during pollution episodes. The present work
indicates that O3 transported on hemispheric scales substantially
impacts air quality in some areas of the US.
Citation: Parrish, D. D., Aikin, K. C., Oltmans, S. J., Johnson, B. J., Ives, M., and Sweeny, C.: Impact of transported background ozone inflow on summertime air quality in a California ozone exceedance area, Atmos. Chem. Phys., 10, 10093-10109, doi:10.5194/acp-10-10093-2010, 2010.