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Abstract: Ground-based zenith-sky DOAS observation was carried out from October 1, 2009 to September 30, 2010 in Shanghai, China to measure the O4 and H2O absorption in visible band and to illustrate the dependence of their correlation slope on the aerosol pollution type. Good correlations between O4 and H2O DSCDs can be found through linear regression analysis whether it was sunny, cloudy, overcast, or rainy. The correlation slope varied seasonally in the order of summer < autumn, spring < winter. In particular, the correlation slope and fluctuation were small in the summer. It was found that slope values also relied on sky conditions generally in the sequence of dusty > sunny > cloudy > overcast > rainy. The implication of the variation of slope to the aerosol pollution type was discussed for typical heavy dust and haze episodes occurred in March 2010 and October 2009, respectively. As the correlation slope abruptly increased during the heavy dust due to low moisture content and enhanced O4 absorption caused by abundant suspended dry crustal particles, the slope dropped suddenly in the haze episode owing to the significant augment of H2O absorption. Thus, the much discrepant correlation patterns may be regarded as a characteristic signature for dust and haze events. [Copyright &y& Elsevier]

Abstract: Observation of NO3 radicals was performed in an urban area of Shanghai using differential optical absorption spectroscopy from August 15 to October 7, 2011. With the exception of the data below detection limit (0.008 ppb), the observed mean NO3 mixing ratios were 0.016 ± 0.009 ppb with a range of 0.008–0.095 ppb. Under the assumption of steady state, the NO3 production rates were calculated ranging from 0.08 ppb h− 1 to 12.85 ppb h− 1 throughout the observation, and averaged at 1.10 ± 1.09 ppb h− 1. The calculated NO3 lifetime was determined from several seconds to a maximum value of about 900 s with an average of 102 ± 93 s. The correlation of NO3 production rates to the NO2 mixing ratio is about 0.76, which is larger than the correlation between NO3 production rates and O3. Hence, the variability of NO3 production mainly results from the ambient NO2 levels present. The positive correlation between the NO3 mixing ratio and its production rates indicates that direct sinks cannot be neglected for the nitrate radical''s chemistry in Shanghai, especially under polluted conditions. However, the slope of the logarithmic correlation between NO3 lifetime and NO2 mixing ratio is very close to −1, which means that the NO3 removal strongly depends on the indirect loss process. Moreover, the atmospheric suspended particles have an important impact on NO3 lifetime because the NO3 removal was accelerated by the high PM10 concentration, e.g. all NO3 lifetime are below 30 s when the PM10 concentration was larger than 0.05 mg m− 3 during the severe pollution episode in October. [Copyright &y& Elsevier]

Abstract: The Yangtze River Delta (YRD) region is one of the most economically developed regions of China and characterized by high level of urbanization, which comes with the consequence of severe deterioration of its atmospheric environment in a large regional scale. In order to characterize the fine particle pollution features representative for YRD, especially for the abundant and complex carbonaceous component, we deployed advanced on-line measurement at a regional site in Jiaxing in the central YRD area during June 29–July 15 (the summer campaign) and December 11–23 (the winter campaign), with a high resolution aerosol mass spectrometer (AMS) and a single particle soot photometer (SP2). The mean PM1 mass concentration was observed to be 32.9 μg m−3 in summer, with organic matter (OM) and black carbon (BC) contributing 32.1 and 9.1%, respectively, and 41.9 μg m−3 in winter, with OM and BC contributing 30.3 and 16.9%, respectively. The O/C ratio of OM, an indicator for the oxidation level of organic aerosol, was calculated to be 0.28 in summer and 0.33 in winter, and the number fraction of internally mixed BC particles (NIB), an indicator for the aging level of BC, was calculated to be 0.51 in summer and 0.53 in winter. Two popular independent methods were used to estimate the amount of secondary organic aerosol (SOA) in Jiaxing: one is the positive matrix factorization method utilizing the high resolution aerosol mass spectra (the AMS-PMF method), and the other is the simple OC/EC ratio method (the OC/EC method). The AMS-PMF method estimated that SOA averagely accounted for 68.3 and 30.2% of OM in summer and winter, respectively. The SOA amount estimated by the OC/EC method was found to agree well with that by the AMS-PMF method in summer, but strong biomass burning events in winter made the OC/EC method over-estimate SOA largely. The seasonal variation of SOA indicates that SOA production in YRD is more determined by ambient temperatures than by precursors. [Copyright &y& Elsevier]

A continuous and heavy photochemical pollution episode when Typhoon Nari occurred during Sep. 14–19, 2001 in Hong Kong was studied by use of the new generation of regional air quality model WRF–chem V2.1, in which the meteorological model (WRF) and chemical model (chem) are fully coupled on line. In this episode, the regional air quality monitoring stations in Hong Kong recorded high concentrations of O3, CO and NO x for six days, the maximum concentration of O3 reached 191ppb, and the atmospheric visibility dropped to 1.8km. Investigations showed that WRF–chem can basically simulate this continuous photochemical pollution episode, with the best correlation coefficient of the simulated and the observed O3 concentrations being 0.84. The production and loss of O3 were significant in this episode, and the largest rates were 22.7 and −17.6ppbh−1, respectively. The simulated meteorological conditions showed high temperature, lower relative humidity, strong solar radiation, northerly airstream, and stable boundary layer structure in Hong Kong during the episode, these weather factors were conducive to formation and maintenance of photochemical pollution. It was also clear that the vertical transport played an important role in this episode. As controlled by downdraft at the outside of Typhoon system with more stable atmosphere, air pollutants were limited and accumulated in the low level of boundary layer, leading to high O3 concentration from photochemical formation. [Copyright &y& Elsevier]