Seasonal variations in diurnal concentrations of trace elements in atmospheric aerosols in Chicago

Atmospheric aerosols are solid or liquid particles dissolved in air, which can change their chemical composition frequently depending, on various parameters such as wind speed and direction. In this study, diurnal atmospheric aerosol filter samples, taken at Loyola University Chicago's Air Monitoring Station, are discussed with respect to variations in trace elemental composition at different seasons. The samples collected, were digested in a microwave oven and analyzed by total reflection X-ray fluorescence (TXRF) spectrometry. To aid interpretation of the samples, meteorological parameters were recorded and back trajectory analysis was employed. Four days, based on average meteorological conditions, were selected for each season as example to obtain preliminary insight into trace elemental variations. The results indicate that elemental concentrations vary during seasons and depend on major wind patterns (speed and direction). The differences were most pronounced in summer, where most elemental concentrations were found to be lowest of all seasons due to onshore (cast) wind from Lake Michigan, depriving the air parcel of larger particles by deposition into the lake. In spring and fall the elemental concentrations determined were much higher, which can be attributed to the prevailing and often stronger westerly winds and associated higher particle freight. In winter the situation can be described as intermediate between summer and spring/fall with moderate elemental concentrations due to weaker winds and less stable wind directions. (C) 2003 Elsevier B.V. All fights reserved.