ATMOSPHERIC TRACER CONCENTRATIONS FROM ELEVATED SOURCE IN URBAN CORE

An understanding of building wake effects is critical to the correct s imulation of near-field dispersion of air pollutants that can be entra ined in the wake cavity. Downwash of effluent plumes from elevated sou rces due to building wake effects can raise atmospheric concentrations of the effluent gas near ground level close to the source. Maximum ob served ground level concentrations can be due to downwash under certai n circumstances. In this field experiment 51 SF6 samplers were deploye d to measure the near-field tracer concentrations due to an elevated p oint source of heated effluent under stable to neutral atmospheric con ditions in an urban core. Over 2,000 hourly samples were collected and analyzed. Isopleths of SF6 hourly concentrations indicate a complicat ed relationship between concentration and the individual and aggregate position, as well as between concentration and the geometry of surrou nding obstacles.