LIDAR, NEPHELOMETER, AND IN-SITU AEROSOL EXPERIMENTS IN SOUTHERN ONTARIO

During August 1992, a complex aerosol and optical experiment was perfo rmed at Egbert, Ontario, Canada. In situ data from Berner impactors, t hree active scattering aerosol spectrometer probes, a differential mob ility analyzer, filter, and denuder samples were intercompared with op tical measurements from a nephelometer and a lidar. A haze event durin g the study period has been modeled using the measured in situ particl e size data and a hygroscopic growth model. Agreement between the mode led and the measured data is good, except in periods of relative humid ities in excess of 90%. Explosive particle growth during the midmornin g hours is explained by gas-particle conversion processes of sulphur-b earing species. The light scattering measurements lead to a specific s cattering coefficient of the dry aerosol of 3.2 m(2) g(-1), but the re sult is clearly dependent on air mass origin and relative humidity. Th e latter result is important in global models of radiative response to anthropogenic aerosol inputs (sulphate aerosol, lidar, nephelometer, light scattering, aerosol radiative forcing).