| Air anion concentration has not only been an important index in evaluating cleanness of the urban air but also been a new tourism resource.Therefore,it is significantly important for urban ecological planning and environmental protection to explore the characteristics of distribution and variation of air ion concentration in Xi'an City.In this thesis,the air ion concentration at four typical urban functional areas in Xi'an city was measured by using DLY-2G air ion monitor from Apr-2008 to Jan-2009.The emphasis here was on the temporal-spatial distribution characteristics of the air ion and the assessment of air quality in Xi'an city from the view of the air ion concentration.Moreover,the correlations between the air ion concentration and the temperature and the relative humidity were also studied preliminary.Firstly,the results show that the air ion concentration at each functional area varies obviously during a day.There are several patterns of daily variations of small air ion concentration at different functional areas,that is,one-peak curve,double-peak curve, pulsation curve and approximate straight line.The fist two kinds of curve exist at the landscape area while the last two appear at the traffic road and factory districts where the air pollution is severe.The concentration of small air ion at the culture and education areas fluctuates frequently.The variations of small air ion concentration are closely associated with the environment factors,the quantity of air pollutants and human activities.The largest value of small air ion concentration appears mostly in the morning and at noon at each functional area.The air ion concentration in summer and spring is obviously higher than in autumn and winter.Secondly,the concentration of small air ions at different functional areas is very uneven. In summer,the average value at landscape area is the largest,at which the concentrations of small anion and small cation are 553 ions/cm~3 and 616 ions/cm~3 respectively,and the annual average is more than 400 ions/cm~3.The annual average values of small anion concentration at the culture and education areas,traffic road and factory district are 222 ions/cm~3,196 ions/cm~3 and 177 ions/cm~3,respectively,while the values of small cation concentration are 261 ions/cm~3,255 ions/cm~3 and 197 ions/cm~3,respectively.The annual minimum of the four functional areas appears at factory district in the winter,and the small anion and cation concentrations are only 138 ions/cm~3 and 155 ions/cm~3 respectively.Perfect green area provides a sharp contrast to the imperfect green area in small ion concentration.The concentration of air ions in an unpolluted area is significantly higher than that in polluted area.Additionally,the air quality at the typical functional areas in Xi'an city has been also assessed by using air ion assessment index based on the air ion concentration from measurements.It is found that the air quality in summer is the best,in spring is better and autumn and winter followed by the worst.In all the four seasons,the air quality of the landscape area is obviously better than the culture and education areas,traffic road and factory district.The air quality of the culture and education areas is a little better than traffic road and factory district.However,the air qualities of these three functional areas are not good,and the necessary measures should be taken to improve the air quality.Finally,it has been found that the small air ion concentration has a negative relation with the ambient temperature in spring,summer and autumn while positive relation in winter.In most cases,there is a positive relation between the small air ion concentration and the relative humidity. |
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