Characteristics And Impact Factors Of Urban Heat Island And Air Pollutants

Abstract:In the recent years,with the acceleration of the urbanization process,city environmental pollution is becoming more and more serious. Particle diameter less than10μm (PM10)can enter human respiratory system and causes much negative health effects to human health,which also have influence on the city air quality and visibility. Because of the characteristics of city itself, determines its surrounding suburbs and rural areas with significant differences in the heat dissipation and thermal properties of materials,resulting in city temperature is high,which form a phenomenon of urban heat island.As particulate matter, high temperature can also cause negative effects on human health.The incidence of mortality and all other kinds of disease is much higher than the surrounding regions.So city air pollution and thermal pollution has become a research hotspot all over the world.In view of this,the research works in this paper mainly includes the following parts:Temporal and spatial variation of heat island area and the influence of wind in Changsha were investigated.Heat island intensity in different seasons and months is small,maximum hourly urban heat island intensity frequency occurs mostly in the evening.Heat island intensity in different city regions in evening was remarkable,which were relatively small especially in the noon.Wind speed and direction have significant influence on the spatial distribution of urban heat island.The effect of wind speed on the urban heat island difference between different monitoring points which parallel with the wind direction is remarkable but the effect can be neglected between monitoring points in the vertical direction of wind.PM10concentration was significantly different in different seasons and time.Generally speaking, the concentration is higher in the cold seasons than hotter seasons.The daily average PM10concentration most appeared between50μg/m3and150μg/m3.The results also showed that traffic source has significantly different contribution to PM10concentration under different daily average concentration conditions,the lower the PM10concentration,the greater contribution of traffic source make to PM10concentration and vice versa. Two methods were developed to improving the accuracy of air pollutants prediction.The method of separation of variables was used to analysis the diffusion and propagation characteristics of air pollutants.The diffusion was significant differences under different atmosphere state, the concentration decline with the increasing distance to the pollutant source and appears a peak value close to the ground.Wind speed has significant effect on the diffusion and propagation of air pollutant.The relationship between heat island intensity and PM10concentration was firstly studied under different meteorologic condition.The correlation coefficient between urban heat island intensity and PM10concentration was positive in all seasons and the correlation coefficent was copositive correlation with PM10concentration.The relationship of urban heat island intensity and PM10concentration showed remarkable discrepant under different meteorological conditions.The model of the effect of urban heat island on the air pollutant diffusion was build and the results showed that urban heat island has significantly influence on pollutant diffusion.The effect was obviously. When wind speed was small,the pollutant concentration was improving due to urban heat island where far away from the center of urban heat island,while the effect was inversely near to the urban heat island center.The method which combined weather systems,atmospheric boundary layer and single meteorological parameters was developed to study the influence of meteorological conditions on the heat island intensity and concentration of pollutants.The influence of meteorological parameters on urban heat island and PM10concentration was significant, as for single parameter, wind speed and relative humidity were more remarkable than others.Weather synoptic pattern and the dynamical characters also have significant effect on urban heat island and PM10concentration.High PM10concentration and strong urban heat island intensity were easy to form under the anticyclone and high pressure ridge weather pattern. Cyclone and cold front synoptic pattern were benefit for forming low air pollution concentration and urban heat island. The dynamical characteristic of atmosphere boundary layer has definitively role on the diffusion of air pollution and heat, which were prone to be diluted under the condition of unstable atmosphere boundary layer in which wind speed was larger, no inversion layer and high mixing layer. On the contrary, high air pollution and strong urban heat island were easy to form under stable atmosphere boundary layer, in which low speed, strong inversion layer and low mixing layer high inside.