The Statistical Characteristics Of Air Pollutant Concentrations And The Relationship Between Meteorological Elements And Pollutants In Xi’an

In recent years, urban air pollution is increasingly serious, and has becomeone of the environmental issues which has aroused the public widely concern.Urban air pollutant concentrations are mainly affected by meteorology, the typeand distribution of pollution sources. The statistical characteristic of pollutantconcentrations is a special case in different area. Therefore, to analyze thestatistical characteristics of urban air pollutant concentrations and discuss therelationship between meteorological elements and pollutants is significant forresearching urban air pollution problems and developing effective mitigationstrategies.In this dissertation, the time series data of three conventional air pollutant(i.e. SO₂, NO₂and PM₁₀) concentrations monitored in Xi’an in2011were taken.The purpose of this paper is to investigate the statistical characteristics ofpollutant concentrations with the statistical methods. On that basis, thesynchronous meteorological data were used to analyze the relationships betweenair pollution concentrations and meteorological factors. The main conclusions are as follows.1. The results of analyzing the observed concentrations of SO₂, NO₂andPM₁₀showed that the hourly concentrations of three air pollutants have obviousseasonal and diurnal variation. The air pollutant concentrations are always highin winter followed by in spring, and lower concentrations in Xi’an are observedin autumn and summer. The diurnal variation curves of PM₁₀and NO₂concentrations are all bimodal with high concentration in morning and low inevening. But, the diurnal variation of SO₂concentration shows a single peakwhich always appears at noon.2. Due to the impact of pollution sources and local wind （direction andspeed）, the concentrations of PM₁₀, SO₂and NO₂in Xi’an have some spatialdistribution properties. The highest PM₁₀concentrations are shown in theMunicipal People’s Stadium and Lin Tong district, and the lowest in Cao Tan.The concentration of SO₂is the highest in the Municipal People’s Stadium andHigh-Voltage Switchgear Factory but near in other monitoring sites. The NO₂concentration of Jing Kai district is maximum while the Xing Qing district isminimum. 3. Four commonly used statistical distribution models were adopted toresearch the optimal distribution of air pollutant concentrations in differentseasons and typical air quality conditions, also the main parameters of the bestdistributions. And using three goodness-of-fit tests to determine the appropriatestatistical distribution model of air pollutant concentrations, including KS, ADand Chi-squared test, respectively.4. The influence of meteorological elements on the air pollutantsconcentration in Xi’an was studied using linear correlation analysis method. Theresults indicated that wind speed, temperature and mixed layer depth all shownegative correlation with pollution concentrations, while air pressure andatmospheric stability are positively correlated with the concentrations ofpollutants.5. The paper analyzed and discussed the meteorological conditions onsituations of the “best” and “worst” air quality. It is concluded that air quality isbetter when there is heavy and continuous precipitation. While serious airpollution will appear easily when there is no precipitation with the lower mixedlayer and higher occurence of calm wind. Besides, wind speed is too large （more than a certain threshold） can also cause particulate pollution.