Incoming Radiation and Vertical Temperature Profiles in a Polluted Urban Atmosphere

Abstract

<p> Simultaneous measurements of incoming short and longwave radiation were made at a rooftop site in the industrial heart of Hamilton, Ontario, and at a control station several miles to the south of the city at Mt. Hope airport. Direct comparison of these measurements was facilitated by selecting clear sky days from the winter solstice to the end of April.</p> <p> Results indicate that the decrease in solar radiation intensity due to atmospheric pollution is balanced by a comparable increase in the flux of incoming longwave radiation from the sky. Receipts of total incoming radiation are therefore the same at both sites.</p> <p> Vertical air temperature profiles over the industrial site and the control site were measured using a specially designed aircraft-mounted sensor. Profiles were determined on the same days that radiation measurements were made.</p> <p> While the temperature profiles at the control site occasionally exhibited a slight subsidence inversion, the industrial profiles consistently showed a marked inversion whose magnitude diminished with increasing solar altitude and increased again toward sunset. This behaviour is attributed to the enhanced shortwave absorptivity and longwave emissivity properties of the polluted atmosphere.</p> <p> The height of the inversion increased during the morning hours and fell again during the afternoon in response to atmospheric convection caused by surface and atmospheric heating during the day. The top of the inversion, however, always coincided exactly with the top of the visible pollution dome.</p>