Photochemical production of ozone in Beijing during the 2008 Olympic Games

摘要

As a part of the CAREBeijing-2008 campaign, observations of O, oxidesof nitrogen (NO and NO), CO, and hydrocarbons (NMHCs)were carried out at the air quality observatory of the Peking University inBeijing, China during August 2008, including the period of the 29th SummerOlympic Games. The measurements were compared with those of theCAREBeijing-2006 campaign to evaluate the effectiveness of the air pollutioncontrol measures, which were conducted for improving the air quality inBeijing during the Olympics. The results indicate that significant reductionin the emissions of primary air pollutants had been achieved; the monthlyaveraged mixing ratios of NO, NO, CO, and NMHCs decreasedby 42.2, 56.5, 27.8, and 49.7 %, respectively. In contrast to the primarypollutants, the averaged mixing ratio of O increased by 42.2 %.Nevertheless, it was revealed that the ambient levels of total oxidant(O = O+NO+1.5 NO) and NO werereduced by 21.3 and 77.4 %, respectively. The contradictions betweenO and O were further examined in two case studies. Ozoneproduction rates of 30–70 ppbv h and OPEx of ~8 mole mole were observed on a clear-sky day in spite of the reducedlevels of precursors. In that case, it was found that the mixing ratio ofO increased with the increasing NO/NO ratio, whereas the NO mixing ratio leveled off when NO/NO>8. Consequently, the ratio ofO to NO increased to above 10, indicating the shift fromVOC-sensitive regime to NO-sensitive regime. However, in the othercase, it was found that the O production was inhibited significantlydue to substantial reduction in the NMHCs. According to the observations, itwas suggested that the O and/or O production rates in Beijingshould have been reduced as a result of the reduction in the emissions ofprecursors during the Olympic period. However, the nighttime O levelsincreased due to a decline in the NO-O titration, and the middayO peak levels were elevated because of the shift in the photochemicalregime and the inhibition of NO formation.