A regional-scale modeling study of Ozone transport from oceanic background to northern Sacramento Valley during ARCTAS/California period

Background O3 transported from the eastern Pacific together with locally-formed ozone contributes to high surface ozone levels in California. Previous model work concluded that in North America background O3 was generally 15~35ppb and decreased on polluted days. However, observations indicate that observed O3 is directly proportional to transported background over northern Sacramento Valley during summertime, and it takes 20~30 hours for O3 to be transported from the coast at 1~2.5km to inland O3 non-attainment areas. In this study the coastal site Trinidad Head and three inland sites in the Sacramento Valley are selected for analysis. Based on 60km/18 layers/6hour resolution calculations using the STEM chemical transport model, we use back trajectory and source contribution analyses during ARCTAS/California period and conclude that observed O3 is proportional to transported background air. In addition, the best correlations are captured between Trinidad Head at 400~1000m and the inland sites, after 36~39 hours transport times. The impacts of model resolution on these results are also evaluated. The results are extended to look at the impact of boundary conditions over the eastern Pacific on predicted surface concentrations of ozone over California using results from the ARCTAS/California experiments.