On the Relation Between the Large-Scale Tropospheric Circulation and Air Quality in Tehran

The large-scale tropospheric circulation can play a controlling role in the accumulation and ventilation of air pollutants. It thus impacts air quality in large urban areas. This paper investigates the statistical relations between the dynamical indices related to circulation in the troposphere and visibility as a surrogate for air pollution in the urban area of Tehran for the climatological period of 1958 to 2013. The dynamical indices are based on jet splitting and Rossby wave breaking at the upper troposphere, eddy kinetic energy, meridional momentum flux, and static stability at the lower troposphere, as well as the high and low surface pressure disturbances. Despite the definite impact of surface pressure disturbances on visibility in Tehran, results show only very weak, if any, relation between the tropospheric circulation indices and visibility in Tehran. The absence of a robust relation is attributed to the slow response of the urban ventilation process to the time evolution of dynamical indices above the boundary layer and particularly at upper troposphere. The complex terrain of the region is likely the main factor creating the slow response.