Observationally based estimates of U.S. background ozone contributions to NAAQS exceedances in California urban areas

David D Parrish1,2, Lindsay M. Young3, Mia H. Newman3, Kenneth C. Aikin3,4 and Thomas B Ryerson3, (1)University of Colorado at Boulder, Cooperative Institute for Research in Environmental Sciences - CIRES, Boulder, CO, United States, (2)NOAA/ESRL/Chemical Sciences Laboratory, Tropospheric Chemistry, Boulder, CO, United States, (3)NOAA/ESRL/Chemical Sciences Division, Boulder, CO, United States, (4)Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, United States