Dynamic and thermodynamic analysis of the urban heat island effect and aerosol concentration
Dynamic and thermodynamic analysis of the urban heat island effect and aerosol concentration
复制标题
DOI：
--
复制
发表时间：
2015
期刊：
影响因子：
--
通讯作者：
Li Yao
中科院分区：
文献类型：
--
作者：
Li Yao
随着城市化进程的加快和城市环境的恶化，城市热岛效应与大气污染物的相互作用越来越受到人们的关注。一方面，热岛效应引起的环流可以重新安排行星边界层大气污染物的分布；另一方面，大气污染物可以通过对辐射过程的吸收和散射效应来影响热岛效应。利用理论模型，在单个大城市和城市群两种类型的城市分布中解析解决了城市热岛效应与大气污染物的关系。将长波辐射吸收光谱分为强弱两部分，将辐射过程表示为温度分布的函数。假设温度随高度呈指数下降，则边界层的三维运动也可以表示为温度分布的函数。如果确定大气污染物的排放强度，则可以确定辐射吸收系数。将这些系数代入温度方程，求解温度方程和计算边界层的三维运动就容易了，而边界层的三维运动又会影响大气污染物的浓度。因此，通过理论将热岛效应与大气污染物耦合。热岛效应直接取决于人为热释放强度。城市规模越大，城市热岛指数越强。当城市面积一定时，城市散射越大，城市热岛指数越弱。这为城市建设和发展中的多城市联合模式提供了一定的理论支持。这种情况与空气污染物浓度类似。排放强度越强，大气污染物浓度越高。同一排放强度下，单个大城市的污染程度要高于城市群。这也意味着多城市的联合城市可以带来更好的空气质量。随着排放强度的增强，热岛效应强度先减小到最小值，然后缓慢增加。气溶胶的散射效应可以通过降低下边界的太阳辐射量来减小温度异常。然而，当污染物浓度足够高时，吸收加热效应可以超过散射冷却效应。在这种情况下，热岛强度将在中等范围内增强。较强的热岛强度可以驱动较强的PBL环流单体，使更多的污染物重新分布和输送到远离排放中心的地方，从而降低污染物浓度。与人为放热对污染物浓度的缓解作用相比，人为放热对城市热岛的驱动作用更为显著。以上结果表明，热岛效应与大气污染物浓度之间的相互作用可以通过一个简单的理论模型进行耦合。一方面，空气污染物可以散射和吸收辐射，从而减弱和增强UHI强度。另一方面，热岛效应越强所产生的环流越强，可以将更多的污染物从排放中心输送出去，减轻空气的污染程度。城市群的城市热岛强度和污染程度都弱于单个大城市，这对城市建设和发展具有一定的理论指导意义。
With the accelerating urbanization and deteriorating urban environment,the interaction between urban heat island(UHI)effect and air pollutants has been attracting more attention.On one hand,the circulation induced by the UHI effect could rearrange the distribution of the air pollutants in the planetary boundary layer(PBL).On the other hand,air pollutants could influence the UHI effect by absorbing and scattering effects on radiation processes.Using a theoretical model,the relationship between UHI effect and air pollutants is analytically solved in two types of city distributions:a single big city and urban agglomeration.Dividing the long-wave radiation absorption spectrum into strong and weak parts,then the radiation processes could be expressed as functions of the temperature distribution.Setting thetemperature declines exponentially with height,then the three-dimensional PBL motion could also be expressed as functions of the temperature distribution.If fixing the air pollutants emission intensity,the radiation absorption coefficients could be determined.Then substituting the coefficients into the temperature equation,it is easy to solve the temperature equation and to calculate the three-dimensional PBL motion which in turn could influence the air pollutants concentration.Therefore,the UHI effect and air pollutants are coupled through the theory.The UHI effect is directly determined by the anthropogenic heat release intensity.The larger a city is,the stronger the UHI is.When the area of a city is given,the more scattering the city is,the weaker UHI is.This provides certain theoretical support for the multi-city conurbation approach in city construction and development.The situation is similar to the air pollutants concentration.Stronger emission intensity corresponds to higher air pollutants concentration.Same emission intensity causes more serious pollution in a single big city than in urban agglomeration.It also implies that the multi-city conurbation could bring better air quality.With strengthening emission intensity,the UHI effect intensity decreases to a minimum value then increasing slowly.The scattering effect of the aerosol could decrease the temperature anomalies by reducing the amount of solar radiation on the lower boundary.However,the absorption heating effect could surpass the scattering cooling effect when pollutants concentration is high enough.The UHI intensity would intensify with a moderate range under this circumstance.Stronger UHI intensity could drive a stronger PBL circulation cell which could redistribute and transport more pollutants far from the emission center hence reducing the pollutants concentration there.Comparing with the relieving effect of the anthropogenic heat release on pollutants concentration,its driving effect on the UHI is more significant.Above results show that the interaction between the UHI effect and air pollutants concentration could be coupled through a simple theoretical model.On one hand,air pollutants could scatter and absorb the radiation hence weakening and strengthening the UHI intensity.On the other hand,the stronger circulation cell induced by the stronger UHI effect could transport more pollutants from the emission center and relieve the contamination extent of the air.Both the UHI intensity and pollution extent are weaker in the urban agglomeration than in a single big city which might provide certain theoretical guide for the city construction and development.