Regional ozone pollution and observation-based approach for analyzing ozone-precursor relationship during the PRIDE-PRD2004 campaign

Abstract An intensive field campaign, Program of Regional Integrated Experiments of Air Quality over Pear River Delta (PRIDE-PRD2004), was carried out in Pearl River Delta (PRD) in October 2004 to provide an in-depth understanding and a comprehensive record of O 3 , PM 2.5 and other air pollutants in this quickly developing region of China. Two super sites, one in Guangzhou urban center and the other at a downwind rural site Xinken, were extensively equipped with research-grade instruments. In addition, 16 stations of the PRD air quality monitoring network participated in the campaign to provide regional scale spatial coverage. We found high levels of O 3 exceeding China's National Standard throughout the PRD region and clear evidence of regional scale photochemical production of O 3 . Furthermore, the data suggested that in situ photochemical production was the primary source of high concentrations of O 3 in the upwind area, and that the ozone photochemical production efficiency was highly non-linear with greater value at lower NO x . This non-linear relationship between photochemical production of O 3 and its precursors has an important implication for the O 3 control strategy. The ozone–precursor relationship was examined by using an observation-based model (OBM). Large positive relative incremental reactivity (RIR) values for VOCs and negative values for NO x were found, suggesting that O 3 production was usually in VOC-limited regime in both Guangzhou and Xinken sites, while reducing NO x could increase O 3 . However, we caution that this conclusion was reached in a campaign of limited time period and the OBM results could differ in other seasons. Finally, high concentrations of HONO were observed at the two super sites. Current known gas phase source of HONO could account for only a fraction of the observed values, particularly at the Guangzhou site. An unknown and presumed heterogeneous source of HONO would be required to sustain the observed concentrations. At these high levels of HONO, the OH concentration and ozone production would be 2–4 times higher than the case with gas phase source only.