Dependence Of Ambition Air Quality On Meteorology Basing On Wavelet Method In Shanghai

In recent years, along with industrial development and rapid growth of urban population, city air pollution becomes serious day by day, which has caused serious threat on people's life and property. Therefore, it is urgent to protect and improve the air quality of Shanghai. The air quality is decided particularly by the nature and discharges of the pollutions, and is also influenced by local meteorological condition. Under different meteorological conditions, the same source of pollution could induce ground pollutant density varying from decuple to centuplicate. In order to improve the air quality in shanghai, it is necessary to study the correlation between this local meteorology condition and the air quality. In addition, the air pollutant concentration has certain annual variation as well as rule of daily change. It has the multi-level time criterion structure and the localization characteristic in the time domain, including the main period change and the point of turning point change. So forecasting the trend on short time and finding the reason of the turning point occurs by the analysis of air pollutant itself rule are necessary.Base on spot measuring hours data from four state controlling spot in the Shanghai environmental monitoring center, separately includes YangPu region fourth floats the dye factory (industry region), the Hongkou region Hainan road (commercial region), the Putuo area environmental monitoring station (residential district) as well as the Dianshanhu Lake environmental monitoring station (clean comparison district) in 12 o'clock ,31^st,December, 2005 -9 o'clock ,11^st,May, 2006, this article adopts the invariable resolution Mexican-Hat wavelet analytic method that can provide the signal the partial information in the time domain and frequency domain to study the frequency range the change rule and the tendency of ambient air quality as well as its relationships with the meteorology .we can obtain the period and abrupt change of the concentration series of ambient air quality and the time and reason why this abrupt change occurred and forecast short period change tendency.This article studies discovered that the change of relative humidity, the temperature and the PM₁₀ approaches in these four districts about half year, whatever first or second cycles and the change of the point of abrupt change. Although in four different regions, first main period of relative humidity, temperature and PM₁₀ all about are 14 days, viz. two weeks, and the second main period about 5 days. The main reason is that the temperature change directly affects the relative humidity change, which is correlated with PM₁₀ change, on the other hand, theirs' first main cycle, mainly caused by the atmospheric low frequency vibration. But the principle period is irrelevant with local weather situation, therefore, the overall situations of these three factors quite similar in four different areas.Contrasting various areas, we discovered that: the change of three air quality factor (SO₂, PM₁₀ and NO₂) in the Hongkou region and YangPu region quite approaches on main period and the point of abrupt change, the first main period about 14 days, the second main period about 5 days, indicates seasonal variation rule of SO₂, PM₁₀ and NO₂ suitable consistency in these two areas. This kind of typical seasonal variation rule is relationship with the weather condition like temperature inversion,wind direction and wind speed. From the uniformity we may estimate that the source and mode of discharges of the sulphur dioxide, the nitrogen dioxide and PM₁₀ have some kind of general character with change rule. The parameter of air quality factors are similar between Puto area inspection station and Qingpu area inspection station, for example, first main periodic variation and the second main period of SO₂ and the NO₂ already approached very much, the first main period about 19 days, the second main period about 5 days. In the point of abrupt change aspect, PM₁₀, O₃ and the NO₂ air quality factor also approached, the reason of which is that the nitrogen oxygen compound was mainly correlated with the vehicle exhaust. With recent years economy development, the vehicle quantity increases in the suburb every year, therefore, nitrogen oxygen compound in the suburb already changed with urban district.Conducting the wavelet analysis to the ozone time series discovered that, the first principal period of the ozone is different with other parameter of various air quality. Besides Qingpu clean district, first principal period of ozone is about 5 days, but other various air quality parameter all above 14 days, which can induced that the change mechanism of the ozone is different with PM₁₀, NO₂ and the SO₂.But the first principal period of the ozone in the Qingpu Dianshanhu Lake has amounted to 20 day, according to the above estimated, the key reason of the ozone change in Qinpu is different with other three areas is that motor vehicle and industry in suburb are less than city .Another reason is that the nitrogen discharged by vehicle and nitrogen oxide compound from combustible mineral fuel as well as hydrocarbon encounter the sunlight in the air ,which possibly transforms to the ozone and forms the photochemical smog pollution.When further studying the reason of the abrupt change points of various air quality factor change, it displayed besides artificial discharges influence the synoptic situation change is the important reason like cold wave, the sand storm, temperature inversion and the thermal island effect.According to the wavelet coefficients of three different scale changes and changes in the contour, we can predict the concentration of pollutants changes trend in the next four or five days. Concentrations of SO₂ and O₃ will continue to decrease in Hongkou district in the next four to five days, however, the concentrations of PM₁₀ and NO₂ firstly decrease and then increase. The concentration of SO₂, PM₁₀ and O₃ will be continued to decrease and then increased but NO₂ increased in Putuo District. The concentration of SO₂, PM₁₀ and NO₂ will decrease firstly and then increase, but the concentration of O₃ firstly got the top value and then decrease in Yangpu and Qingpu district.These forecast values are consist with the observations.In short, Wavelet transform method overcomes the shortcomings of the Fourier-transform analysis .The Fourier-transform analysis can not be achieved time-domain localization and short-time Fourier analysis window size can not regulate with frequency changes. Wavelet analysis method not only recognizes the principal period implied in the quality of air time series, but also able to give the local structure in the same synchronization with their time-frequency, moreover, it provides a new way to analyze the change of strength in the multi-temporal-scale, distributingand the point of abrupt change that occurred at a specific time of air quality.