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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]

Long-term observation of atmospheric nitrous acid (HONO) was performed from August 2010 to June 2012 in urban area of Shanghai, China. In total, valid data for nineteen months were obtained. The monthly average HONO mixing ratio varied from 0.60 ppb in February 2011 to 1.20 ppb in December 2010, but no obvious monthly or seasonal variations were observed. The mean mixing ratio of HONO was obtained as 0.92 ± 0.57 ppb, with average HONO mixing ratio of 1.08 ± 0.63 ppb for night-time, and 0.76 ± 0.44 ppb for daytime. It was found that HONO mixing ratio is dependent on NO2 mixing ratio both in daytime and at night. Besides, high HONO level during daytime implicates that strong daytime sources must be active in Shanghai. The ratio of HONO to NO2 varied from 0.3% to 42.3% with a typical error of 1% and more than 99% of them below 17%. When NO2 mixing ratio was above 30 ppb, the HONO/NO2 ratio (HONO/NO2 averaged over 5.0 ppb intervals of NO2 mixing ratio) was nearly constant at 3.3 ± 0.2%. When the NO2 mixing ratio is below 30 ppb, however, the HONO/NO2 ratio appeared to increase as the NO2 mixing ratio decreased. Additionally, HONO/NO2 ratio depends obviously on relative humidity at night, while there is no obvious correlation between them during daytime. The average conversion frequency of HONO in sixteen selected days was about 0.007 h−1 under different NO2 pollution scenarios and higher conversion frequency tends to be occurred at lower NO2 levels. [ABSTRACT FROM AUTHOR]

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]