Radiation, Temperature and Atmospheric Emissivities in a Polluted Urban Atmosphere at Hamilton, Ontario

Abstract

Simultaneous measurements of global solar and incoming longwave radiation are presented for roof-top sites in a heavily polluted zone and relatively clean control sites in and around Hamilton. The measurements were taken intermittently under clear skies over a 3-year period. During part of the study vertical temperature profiles were measured between 150 and 2500 m in the industrial and control atmospheres. Solar radiation was strongly attenuated by the industrial atmosphere whereas the daytime incoming infrared flux was increased so that the latter generally compensated fully for the former and the total radiation reaching the ground was similar at both the industrial and control sites. Vertical temperature profiles show that an elevated inversion develops anywhere between 1070 and 1980 m in the industrial atmosphere depending on the season. Prier to early afternoon the inversion weakens and moves upward but in the late afternoon it both strengthens and descends. The rate of atmospheric temperature changes beneath the elevated inversion is substantially greater than in the control atmosphere. An hypothesis is advanced that heavy particulate concentrations in Hamilton's atmosphere play a dual role in absorbing and reflecting solar radiation and in increasing radiative emissivity and absorptivity so that the heat energy from the absorbed solar radiation and absorbed outgoing infrared radiation is rapidly dissipated. This hypothesis is supported by the fact that average atmospheric temperatures in the industrial and control atmospheres do not differ significantly.