III. ENVIRONMENT MONITORING AND URBAN PLANNING
A. Environmental quality in Shanghai
In 1994, the monitoring data of air quality in Shanghai, such as sulphur dioxide, nitrogen oxides, total suspended particulate matter, smoke, sulphuration rate, fluoride, carbon monoxide, precipitation, and Pb, were assessed according to the class 2 standard of the National Air Quality Standard (GB3095-82).
(a) Sulphur dioxide
The annual average concentration of sulphur dioxide in Shanghai was 0.038 mg/m3, which meets the class 2 standard in National Air Quality Standard (GB3095-82). But the concentration varied sharply (figures 21 & 22); the concentration in urban area exceeded the limits in class 2 standard for air quality, while in the suburbs it was lower. The lowest, which is only l6 per cent of the limit in standard concentration, was observed in adjacent counties. The seasonal variation also showed that in urban areas the concentration of SO2 is relatively higher in winter and spring, and then declined in the summer months, June to August. However, in the suburbs and adjacent counties the seasonal change was insignificant. There are two factors that influence the temporal variation and spatial distribution of SO2 in Shanghai: one is the total emission volume which dictates that the concentration of SO2 in urban areas is higher than that in the suburbs and adjacent counties, and the other is a meteorological factor. In winter and spring, inverse temperature layers near the ground and relatively low wind velocities occur frequently in Shanghai and make a significant contribution to the annual peak concentration of SO2 in that period. For instance, the average daily concentration of SO2 was as high as 0.2mg/m3 when the inverse temperature layer of 500m in thickness occurred in the last ten days of January 1994. In summer, when Shanghai enters into its rainy season, the heavy rains and tropical storms greatly contribute to the lower concentration of SO2 during that period. -
Figure 21. The yearly variation in annual daily SO2 concentration in Shanghai
The concentration of SO2 variation has been lessened (figure 21). Despite the increase by 70 per cent of coal consumption in the whole city, from 20.817 million tons in 1985 to 35.13 million tons in 1994, the SO2 concentration in the whole city and in the urban area reduced by 47 per cent and 52 per cent respectively. Ten years ago the industrial block in Xinhua Road was heavily polluted by SO2. Then, the concentration amounted to 0.16 mg/m3, whereas now the concentration can meet the limit of class 2 standard for air quality.
(b) Nitrogen oxides
In 1994 the concentration of nitrogen oxides could easily meet the limits in class 2 standard for air quality in the whole city except the urban area where the concentration of nitrogen oxides only exceeded the limit by 9.8 per cent. The seasonal variation is almost the same as that of SO2. The characteristics of spatial variation of the concentration, which has formed since the mid-1980s, is that such concentrations in ChangNing, YangPu, and HongKou districts are higher than other areas (figures 20 & 21).
Figure 22. The yearly variation in annual daily NOx concentration in Shanghai
The monitoring data revealed a trend of NOx concentration slowly increasing since the mid-1980s, reaching its peak in the period 1990-1993 and then being controlled in 1994 as indicated by the fact that NOx concentration in the whole city and in the urban area reduced by 12.5 per cent and 21.1 per cent respectively compared with that of 1993 (figure 22).
(c) Total Suspended Particulate (TSP)
The monitoring data in 1994 showed that the TSP concentration in the urban areas and in the whole city was 0.29 mg/m3 and 0.247 mg/m3 respectively. It was obvious that the degree of TSP pollution is heavier than SO2 and NOx because of the high average diurnal TSP concentration and high rate of exceeding the limits in the class 2 of the air quality standard. The seasonal variation of TSP had the same trend as SO2. The characteristic of TSP spatial variation was that the high TSP concentration covered a large area (figure 23) due to the solid particles caused by the large- scale infrastructure construction and heavy traffic. In the mid-1980s, the high TSP concentration only covered the area around the XinHua Road and industrial blocks in YangPu district. Now these two distinct islands of high TSP concentration were replaced by high TSP concentration over the whole city indicating that the cause of TSP pollutants has changed from industrial emissions to particles released by infrastructure construction. In 1994 the TSP concentration in the urban area decreased by 5.4 per cent compared with that of 1993, and the concentration in the whole city was almost the same as in 1993 but reduced by 12.2 per cent compared with that in 1990.
Figure 23. The spatial variation of TSP concentration in Shanghai in 1994 (mg/m3)
In 1994, the average monthly dustfall was 12.62 ton/km2 in the whole city, thus exceeding the class 2 in standard for air quality by 59.4 per cent, which was the worst of all the monitoring variables. The dustfall pollution in winter and spring was heavier than in summer and autumn due to the burning of more coal in the colder seasons. The combustible organic matter accounted for 23.8 per cent of the content in dustfall. The characteristics of dustfall spatial variation (figure 24) show that in the mid-1980s there were three high value areas located in XingHua Road in ChangNing and LuWan districts, industrial blocks in YangPu district, but the pollution in the above areas had been controlled and improved. The new high dustfall areas were in LongHua in the southwest, and part of ZhaBei district in north, which was similar to that of TSP.
Figure 24. The yearly variation of dustfall volume in Shanghai
Although dustfall pollution is still heavy, it has been alleviated year by year. This positive outcome is due to the designation of "no black smoke zones" and then "zones with smoke-and-dust under control". If the trend continues, the dustfall in the urban area will meet the class 2 standard by1997.
(e) Acid rain
In 1994, the average pH of rainwater was 5.42 in Shanghai. The frequency of acid rain was 15.9 per cent assessed by the national standard, in which the acid rain is defined as having a pH lower than 5.60. The pH of rainwater and the frequency of acid rain are 5.68 and 13.8 per cent the urban area; The two variables vary insignificantly between the urban area, the suburbs and the adjacent- counties. The low pH of rain water in winter and spring is consistent with the small precipitation in -those season. ln the spatial variation of pH rainwater in the urban area (figure 25), two low value areas were located around the Jin'an Temple and in HongKou district, partly overlapping the high concentration areas of SO2 and NOx. The average ion concentration in rainwater from high to low is: SO 2->Ca2+>NH+>Cl->NO-, indicating that sulphur oxides and nitrogen oxides are the main constituents in acid rain in Shanghai. Compared with the spatial variation of pH in 1986, the low value area has become distinctly smaller.
Figure 25. Acid rain in Shanghai
(f) Other monitoring variables
It is noteworthy that in l994 the concentration of carbon monoxide and Pb increased. For instance, the average concentration of carbon monoxide increased by 48 per cent compared with that in 1993. Spatially, the concentration of the two variables in the urban area is obviously higher than in the suburbs and adjacent counties due to the large number of motor vehicles, heavier traffic and low motor vehicle velocity. In the future, more effort must be made in atmospheric environmental protection in order to control the emission of motor vehicle's exhaust gases.
(g) The comprehensive assessment of air quality
To evaluate air quality by the comprehensive atmospheric index method, the value of four monitoring variables such as SO2, NOX, TSP and dustfall in the urban area, suburbs, adjacent counties and in the whole city are adopted to calculate the above index* and the pollution load coefficient**—the degree of single pollutant's contribution to the air pollution, to decide the main pollutant in air pollution. The result indicates that the air pollution level declines from the urban area to the suburbs and then to adjacent counties. In addition, the pollutant's concentration distribution, of which the highest concentration frequently occurs in industrial blocks in the north and south of the central city, is consistent with the industrial allocation. According to the coefficient calculated, the main pollutants of air pollution in the urban area and in the suburbs in order are dustfall, TSP, NOx and SO2; and in adjacent counties the order is TSP, dustfall, NOx and SO2. For example, the pollution load coefficient in the urban area of TSP plus dustfall reaches 65 per cent, which demonstrates that air pollution is mainly caused by dust.
In recent years, air pollution in Shanghai has been alleviated significantly with the decrease of SO2 and NOx concentrations, the pH value of rainwater has increased and acid rain became more infrequent. As the city continues to grow, the dust raised by the large volume of infrastructure construction and heavy traffic, plus heavier Pb and carbon monoxide pollution, should be given a greater priority in air pollution protection.
Shanghai is a populous industrial metropolis. It's unique urban climate is characterized by heat island effect, dry island effect and dust island effect, of which heat island effect is the principal cause of the other two conditions. This type of climate strengthens the accumulation of pollutants in the city centre, and therefore has a particularly aggravating impact upon air pollution in Shanghai.
Figure 26. Air pollution load co-efficient in Shanghai urban area