On the relationship between ozone and its precursors in the Pearl River Delta: application of an observation-based model (OBM)

Background, aim, and scope Photochemical smog, characterizedby high concentrations of O3 and fine particles, is ofgreat concern in the urban areas, in particular megacitiesand city clusters like the Pearl River Delta.Materials, methods, and results Ambient ozone (O3) and itsprecursors were simultaneously measured at two sites in thePearl River Delta, namely, Wan Qing Sha (WQS) inGuangzhou and Tung Chung (TC) in Hong Kong, from23 October to 01 December 2007 in order to explore theirpotential relationship. Eight high O3 episode days wereidentified at WQS and two at TC during the samplingcampaign, indicating a more serious O3 pollution inGuangzhou than in Hong Kong. An observation-basedmodel was employed to determine the ozone–precursorrelationship. At both sites, O3 production was found to bevolatile organic compound (VOC)-limited, which is consistentwith previous observations. Anthropogenic hydrocarbonsplayed a key role in O3 production, while reducingnitric oxide emissions aided the buildup of O3 concentrations.Among VOC species, the summed relativeincremental reactivity (RIR) of the top 12 compoundsaccounted for 89% and 85% of the total RIR at WQS andTC, respectively, indicating that local photochemical O3formation can be mainly attributed to a small number ofVOC species.Discussion and conclusions A large increment in bothsimulated HO2 and O3 concentrations was achieved withadditional input of hourly carbonyl data. This suggestedthat apart from hydrocarbons, carbonyls might significantlycontribute to the O3 production in the Pearl River Delta.