Modeling of the Effects of Gaseous and Particulate Pollutants in the Urban Atmosphere. Part I: Thermal Structure

Abstract

The short-term effect of radiatively participating pollutants upon the temperature distribution in the boundary layer of the urban atmosphere is predicted. This is accomplished by constructing a mathematical model for atmospheric radiation transfer and one-dimensional mass, momentum and energy transport in the planetary boundary layer. The atmosphere, consisting of gaseous and particulate pollutants as well as natural constituents, is considered to absorb, emit and scatter anisotropically radiant energy. A series of numerical simulations of the thermal structure in the urban atmosphere is performed for summer and winter conditions, with and without an elevated inversion. The numerical simulations stowed that the aerosol pollutants reduced the solar radiant flux at the surface which in turn lowered its temperature during the day. The additional solar heating due to the pollutants caused the atmosphere to be slightly warmer at higher altitudes. The surface temperatures during the day were slightly higher for non-absorbing aerosols than for aerosols with some absorption. Under the conditions investigated the largest surface temperature reduction was 2C, and the maximum rise of the atmospheric temperature due to the additional solar heating was about 1C after a two-day period. The gaseous pollutants increased the downward thermal radiation flux and thus raised the surface temperatures at night. The maximum predicted surface temperature increase was about 3C after a two-day simulation. The pollutant gases were shown to enhance the net radiative cooling below a stable region. This additional cooling modified both the nighttime stable layer and the elevated inversion by causing an upward motion of the stable regions. Thus, radiatively participating pollutants were shown to have the potential for changing the thermal structure of an urban atmosphere.