[1] Total reactive nitrogen oxides (NO y ) are among the key components in the chemistry of ozone production. In order to improve the understanding of the formation mechanisms of high-ozone events in Beijing, China, an intensive experiment on the reactive nitrogen oxides was carried out at the observatory of Peking University during the Campaign of Air Quality Research in Beijing and surrounding areas in 2006 (CAREBeijing-2006) campaign. In this study, analysis focusing on the data of high O 3 episodes was performed to examine the relationship between the concentration of total oxidant and the composition of NO y . High levels of NO and NO y were observed in the morning rush hours, indicating the influences of fresh emissions from local traffic. However, the ratio of [NO] to [NO y ] was only 11-60% in the morning, implying that there was a substantial amount of aged air pollutants remained overnight in the stagnant air mass. Significant increases in the NO z mixing ratio (= [NO y ]-[NO x ]) were observed during the period from the morning toward early afternoon, consistent with the increasing oxidant level. Ozone production efficiency of NO x (OPE x ), which was derived from the NO z -O x regression, was found to range from 3.9 to 9.7 mol/mol in Beijing. Furthermore, it was revealed that the daily [NO z ] maximum was proportional to the NO x peak level in the morning, and that OPE x decreased with the increases of [NO z ] in a hyperbolic form. According to the results, abatement in NO x emission would not be effective toward reducing ozone concentrations in Beijing.
Abstract. As a part of the CAREBeijing-2008 campaign, observations of O 3 , oxides of nitrogen (NO x and NO y ), CO, and hydrocarbons (NMHCs) were carried out at the air quality observatory of the Peking University in Beijing, China during August 2008, including the period of the 29th Summer Olympic Games. The measurements were compared with those of the CAREBeijing-2006 campaign to evaluate the effectiveness of the air pollution control measures, which were conducted for improving the air quality in Beijing during the Olympics. The results indicate that significant reduction in the emissions of primary air pollutants had been achieved; the monthly averaged mixing ratios of NO x , NO y , CO, and NMHCs decreased by 42.2, 56.5, 27.8, and 49.7 %, respectively. In contrast to the primary pollutants, the averaged mixing ratio of O 3 increased by 42.2 %. Nevertheless, it was revealed that the ambient levels of total oxidant (O x = O 3 +NO 2 +1.5NO z ) and NO z were reduced by 21.3 and 77.4 %, respectively. The contradictions between O 3 and O x were further examined in two case studies. Ozone production rates of 30-70 ppbv h −1 and OPEx of ∼8 mole mole −1 were observed on a clear-sky day in spite of the reduced levels of precursors. In that case, it was found that the mixing ratio of O 3 increased with the increasing NO 2 /NO ratio, whereas the NO z mixing ratio leveled off when NO 2 /NO>8. Consequently, the ratio of O 3 to NO z increased to above 10, indicating the shift from VOC-sensitive regime to NO x -sensitive regime. However, in the other case, it was found that the O 3 production was inhibited significantly due to substantial reduction in the NMHCs. According to the observations, it was suggested that the O 3 and/or O x production rates in BeijingCorrespondence to: C. C.-K. Chou (ckchou@rcec.sinica.edu.tw) should have been reduced as a result of the reduction in the emissions of precursors during the Olympic period. However, the nighttime O 3 levels increased due to a decline in the NO-O 3 titration, and the midday O 3 peak levels were elevated because of the shift in the photochemical regime and the inhibition of NO z formation.
The first observation of the photothermoelectric effect in a nanoporous silicon (NPSi) device indicates that the photocurrent is dependent on the position of light-induced local heating from illumination at the Au-electrode/NPSi interface.
This study investigated seasonal variations in the mass concentration and chemical composition of ambient aerosols observed at three stations (coastal, mountainous, and downtown sites) in northern Taiwan from March 2009 to February 2012. The results show that the major aerosol components include ammonium, sulfate, nitrate, sea salt, dust, organic carbon, and elemental carbon, whereas the mass fraction of each species depends on the sampling location and season. A significant correlation (r = 0.7–0.8) was observed in aerosol concentrations measured at the respective stations, indicating that aerosol concentrations were dominated by regional‐scale factors. Ammonium, sulfate, and nitrate consistently reached respective peak values in the spring in conjunction with dust particle levels. This shows that the transport of dust and particulate air pollutants from the Asian continent has affected the atmospheric environment in this area. Distinct seasonality was observed for sea salt and secondary organic carbon (SOC): sea salt levels peaked in the autumn, whereas SOC levels peaked in the summer, implying that their sources were regulated by independent seasonal factors. Correlation between sea salt concentration and surface wind speed was derived from coastal measurements and showed a high value for the wind speed sensitivity parameter of around 0.37 for our location. In addition, it was revealed that the SOC concentration in aerosols was positively correlated with oxidant photolysis index (Ox × UVB), suggesting that the SOC seasonality was dominated by hydroxyl radical production.
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