| An observational study on the temporal and spatial distributions of atmospheric NO2, O3, SO2, and HONO (gaseous nitrous acid) in both urban and surban area of Shanghai was carried out in the study, by means of active multi-axis DOAS (differential optical absorption spectroscopy).Chapter 2 describes an active multi-axis DOAS system developed by ourselves. The system has 4 transmitting/receiving telescopes integrated together and can project 4 independent measuremental beams. The beams share one xenon short-arc as the light source. The angle between different beams can be adjusted up to 28°. The concentrations of the air pollutants among the 4 beams can be measured simultaneously. The inherent difference in measurement between different beams was then examined, in the way that the 4 beams were set to point at the same retro-reflector and measure the concentration of NO2 in the same area. Their measurement results were compared with each other by linear regression. The comparison shows good consistency between the results from the 4 beams. The correlation coefficient (R2) between the measurement results from any two beams is no less than 0.97, and the average difference between them is smaller than 1 ppb.The formal observation has two periods. Chapter 3 refers to the first peroid, during which the observation was mostly focused to study the vertical distribution of air pollutiontants, and only one pollutant species could be measured at a time. In the site of Fudan University (FDU) that locates in the urban area of Shanghai, NO2 and SO2 were observed for about a month respectively. Chapter 4 refers to the second period, during which the time variation of pollutants and the relationship between different species were more concerned. The simultaneous measurement of 4 pollutant species in this period accumulated an amount of data of more than a year. Moreover, a comparison observation was carried out in a rural site of Fenhu (FH).During the first period, with a planar CCD sensor employed to detect the spectra, the vertical profiles of air pollutants were observed in the FDU site. The vertical region of observation was 0-88 m, and was equally devided into 4 layers. The vertical distribution of NO2 was measured for almost a month from Oct to Nov,2008. The vertical distribution of SO2 was measured for a little more than a month from Apr to Jun,2009. The study of this peroid got the conclusions as follows:(1) The diurnal variation of NO2 shows a double-peak pattern, the 2 peaks occur in the early morning and the evening respectively, while the valleys occur in the afternoon and the wee hours. The vertical profile shows that the layer of 44-66 m has the highest NO2 concentration, while the layer of 66-88m the lowest. The vertical gradient of NO2 is relatively higher at night and lower in the day; the maximum gradient occurs in the evening, while the minimum occurs in the morning, with a biggest inter-layer difference of 17 ppb and 3 ppb, respectively.(2) The concentration of SO2 varies rather randomly. The average diurnal variation exhibits a single-peak pattern with the peak in the morning. The vertical distribution of SO2 in the observation region is relatively even, with the biggest inter-layer difference of 3 ppb. The concentration in the layers of 44-66 m and 0-22 m is a little higher than that in the other two layers, exhibiting an anti-S shaped average vertical profile. When the SO2 concentration is low, the concentration near ground is slightly higher than that in the upper layers; but when polluted air mass arrives, the concentration in the upper layers becomes higher than that near ground.During the second period, with an integrated PDA spectrometer employed to detect the spectra, the concentrations of NO2, O3, SO2, and HONO were measured simultaneously. But for the sake of the spectrometer, the pollutants were measured in only one beam. The measurement in the FDU site lasted from Jun 2009 to Oct 2010; the comparison measurement in the FH site lasted from Jul 2010 to Oct 2010. According to the measurement results, studies were made on the diurnal and seasonal variation of the 4 pollutant species, the relationship between meteorological factors and pollution degree, the weekend effect, and the impact of HONO on photochemical pollution. The pollution patterns of the 2 sites were compared as well. The following conclusions were made:(1) In the FDU site, the diunal variation of NO2 exhibits a double-peak pattern all year long, with the peaks occur in the early morning and the evening, and the valleys occur in the afternoon and the wee hours. The seasonal variation profile of NO2 is winter>fall>spring>summer. The analysis according to meteorological factors proves that the FDU site is in a region with relatively high NO2 concentration; there is an evident negative correlation between the concentration and wind-speed; the sensitivity with wind-direction is also found to be a little strong. The NO2 concentration in the FDU site has an obvious weekend effect, with an average concentration during evening rush hours on weekdays 6 ppb higher than that on holidays. In the FH site, the diunal variation of NO2 exhibits a single-peak pattern with the peak and valley occur in the wee hours and the afternoon, respectively. The average NO2 concentration in the FH site is lower than that in the FDU site.(2) The diurnal viariation of O3 exhibits a single-peak pattern in the both sites, with the peak and valley occur in the afternoon and the wee hours, respectively. The seasonal variation profile of O3 in the FDU site is spring> summer>fall>winter. The analysis according to meteorological factors proves that O3 is realitively well-mixed near the FDU site; the impacts on the O3 concentration of wind-speed and wind-direction are both found to be low. Serious photochemical pollution was observed in Fenhu, with a highest O3 hourly average concentration of 211 ppb.(3) The diurnal variation of SO2 in different seasons exhibits the patterns of single-peak or multi-peak; the main peak usually occurs in the early or the late morning. The seasonal variation profile of SO2 in the FDU site is winter>fall>spring>summer. The average concentration in winter is 2.4 times as high as that in summer; the daily variation of SO2 in winter is found to have an anticorrelation with the variation of temperature. The analysis according to meteorological factors proves that the FDU site is in a region with low SO2 concentration, but there are polluted regions nearby. Such distribution made the SO2 concentration in the site a strong sensitivity with wind-direction, and also a special kind of correlation with wind-speed that they're hardly correlated when wind-speed is below 2 m·s-1, but negatively correlated when wind-speed is below 2 m·s-1. The SO2 concentration measured in the FH site is almost equal to that in the FDU site during the same period.(4) The diurnal viariation of HONO exhibits a single-peak pattern in the both sites, with the peak and valley occur in the early morning and the afternoon, respectively. The seasonal variation profile of HONO in the FDU site is summer>fall≈winter>spring. The HONO concentration in the summer of 2009 is much higher than that in the summer of 2010, with a highest hourly average concentration of 7.43 ppb. The analysis according to meteorological factors proves that the FDU site is in a region with relatively high HONO concentration; the concentration has an evident negative correlation with wind-speed, and also a strong sensitivity with wind-direction. The maximum HONO eoncentration in the morning correlates to the intensity of photochemical pollution in the same day in a certain extent; the collrelation is relatively high in fall and winter, but low in summer. The nocturnal HONO concentration in the FH site is slightly higher than that in the FDU site, but the daytime concentrations in the two sites are almost equal.
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