|Alternative Title||Study on urban-exurban differences of ambient air quality in Beijing|
|Place of Conferral||北京|
|Keyword||空气污染 Air Pollution 城郊差异 Urban-exurban Differences 影响因素 Influencuing Factors 北京 Beijing|
|Other Abstract||Air environment quality is closely related to urban comprehensive competitive power. It affects urban investment environment, residents’ health and sustainable urban development directly. As the capital city and economic and political centre of China, Beijing’s rapid development has caused soaring energy and resource demand, increasing motor vehicle quantities and spreading of constructions sites, which can affect urban air quality directly. In this study, the concentrations of air pollutants SO2, CO, NOx, O3 and PM2.5 in three representative regions of Beijing i.e. central urban, urban-fringe and exurban were analyzed based on the data from 2008 to 2010. Study on urban-exurban differences of air environment quality and its influencing factors is an important topic. It can provide scientific basis for the formulation of air pollution control measurements. Main results and conclusions are as follows:|
1) Comparisons of air environment quality between central urban and urban-fringe regions: the monthly variation trends of SO2, CO and NOx were similar, so were the seasonal variation trends. Generally, the average concentrations in January and December were higher than those in other months, while the average concentrations from May to August were lower than those in other months. The seasonal variations of SO2, CO and NOx concentrations showed such patterns: winter > autumn > spring > summer. The SO2 and NOx concentrations in central urban region were generally lower than those in urban-fringe region due to the residents’ domestic use of coal burning in urban-fringe region. The differences of CO concentrations between the two regions were not obvious, which might be due to complicated CO sources. The O3 concentration also showed distinct changes over months and seasons. The average O3 concentrations from Jun to August were 1.9-5.5 times the concentrations in January and December. The O3 concentration was highest in summer, and lowest in winter. The O3 concentrations between the two regions had little differences.From January 2008 to March 2009, the average mass concentration of PM2.5 in urban-fringe region was 59.1μg/m3, which was 36% lower than that in central urban region. However, from March 2009 to December 2010, the average mass concentration of PM2.5 in urban-fringe region was 95.5μg/m3, which was 60% higher than that in central urban region. The differences of PM2.5 mass concentrations between the two regions were closely related to construction activities nearby. Overall, the differences of SO2, CO, NOx and O3 concentrations between central urban and urban-fringe regions were not significant (P>0.05). However, the difference of PM2.5 concentrations between the two regions was significant (P=0.027).
2) Comparisons of air pollutants in central urban, urban-fringe and exurban regions: the diurnal changes of SO2, CO and NOx concentration showed two peaks’ types in four seasons in central urban and urban-fringe regions, which were consistent with the characteristics of anthropogenic activities. However, no obvious diurnal variations in SO2, CO and NOx concentration were found in exurban region. The concentrations of SO2, CO, NOx were significantly higher in winter than those in summer, indicating the impact of winter heating in Beijing and low atmospheric boundary layer. Moreover, the diurnal change in O3 concentration showed one peak pattern at four seasons, suggesting the leading role of local photochemical formation. The O3 concentration in central urban and urban-fringe regions dropped to nearly zero at night. In central urban and urban-fringe regions, a large number of NO emission sources at night may play an important role in titration of O3, which can lead to great reduction of O3 concentration. Furthermore, the O3 pollution was serious in spring and summer, but light in winter. The diurnal variation of PM2.5 in central urban showed two peaks’ patterns with one peak from 7:00 to 10:00 in the morning, another around 0:00 at night. The PM2.5 concentrations in urban-fringe and exurban regions both had several peaks within a day. In these two regions, the PM2.5 concentrations from 7:00 to 11:00 and from 16:00 to next 0:00 were higher than those in other hours. The serious PM2.5 pollution in exurban might be related with mining activities nearby. Overall, the concentrations of SO2, CO, NOx in central urban and urban-fringe regions were higher than those in exurban region, whereas the O3 concentration showed an opposite distribution. The PM2.5 pollution in urban-fringe ergion was the most serious, followed by exurban. The PM2.5 pollution in central urban region was the lightest.
3) The correlations between air pollutants and meteorological factors: SO2, CO, NO and NO2 were negatively correlated with temperature, wind speed and solar radiation, but positively correlated with relative humidity and air pressure. O3 had opposite coefficients with above meteorological factors as apposed to these primary pollutants. Further research showed that solar radiation was the most important meteorological factor impacting O3 concentrations in the daytime. The correlation coefficients between PM2.5 concentration and temperature, wind speed, solar radiation and air pressure were not significant. PM2.5 concentration had significantly positive correlations with relative humidity.
4）Comparisons of elemental compositions (i.e. Al, As, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, Pb, Se, V and Zn) in central urban and urban-fringe regions: the differences of crustal elements Al, Ca, Fe, K ,Mg, Na concentrations in PM2.5 samples between the two regions were largest. The enrichment factors of the other elements (As, Cd, Co, Cr, Cu, Mn, Ni, Pb, Se, V and Zn) in urban-fringe region were generally higher those in central urban region, especially for Pb and As, which might be related to secondary pollution of contaminated soil and buildings near urban-fringe region. Dust from the surface and construction sites may be the main reason for the serious PM2.5 pollution in the two regions.
5）The urban-exurban differences of air environment quality in Beijing are effected by joint action of natural and anthropogenic factors. However, the main sources of air pollution in Beijing are human activities, such as coal burning, motor vehicle exhaust, construction. Thus, strengthening the management and restriction of human activities is an important way to control urban air pollution and improve the quality of air environment in Beijing.
|王姣. 北京市城郊空气质量差异研究[D]. 北京. 中国科学院研究生院,2011.|
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