Process analysis and sensitivity study of regional ozone formation over the Pearl River Delta, China, during the PRIDE-PRD2004 campaign using the Community Multiscale Air Quality modeling system

摘要

In this study, the Community Multiscale Air Quality (CMAQ) modeling systemis used to simulate the ozone (O₃) episodes during the Program ofRegional Integrated Experiments of Air Quality over the Pearl River Delta,China, in October 2004 (PRIDE-PRD2004). The simulation suggests that O₃pollution is a regional phenomenon in the Pearl River Delta (PRD). ElevatedO₃ levels often occurred in the southwestern inland PRD, Pearl Riverestuary (PRE), and southern coastal areas during the 1-month field campaign.Three evolution patterns of simulated surface O₃ are summarized basedon different near-ground flow conditions. More than 75% of days featuredinteractions between weak synoptic forcing and local sea-land circulation.Integrated process rate (IPR) analysis shows that photochemical productionis a dominant contributor to O₃ enhancement from 09:00 to 15:00 localstandard time in the atmospheric boundary layer over most areas withelevated O₃ occurrence in the mid-afternoon. The simulated ozoneproduction efficiency is 2–8 O₃ molecules per NO_x moleculeoxidized in areas with high O₃ chemical production. Precursors ofO₃ originating from different source regions in the central PRD aremixed during the course of transport to downwind rural areas duringnighttime and early morning, where they then contribute to the daytimeO₃ photochemical production. The sea-land circulation plays animportant role on the regional O₃ formation and distribution over PRD.Sensitivity studies suggest that O₃ formation isvolatile-organic-compound-limited in the central inland PRD, PRE, andsurrounding coastal areas with less chemical aging (NO_x/NO_yx-limited in the rural southwestern PRD with aged air(NO_x/NO_y<0.3).