During August 1992, a complex aerosol and optical experiment was performed at Egbert, Ontario, Canada. In situ data from Berner impactors, three active scattering aerosol spectrometer probes, a differential mobility analyzer, filter, and denuder samples were intercompared with optical measurements from a nephelometer and a lidar. A haze event during the study period has been modeled using the measured in situ particle size data and a hygroscopic growth model. Agreement between the modeled and the measured data is good, except in periods of relative humidities in excess of 90%. Explosive particle growth during the midmorning hours is explained by gas-particle conversion processes of sulphur-bearing species. The light scattering measurements lead to a specific scattering coefficient of the dry aerosol of 3.2 m2 g-1, but the result is clearly dependent on air mass origin and relative humidity. The latter result is important in global models of radiative response to anthropogenic aerosol inputs (sulphate aerosol, lidar, nephelometer, light scattering, aerosol radiative forcing). ¿ American Geophysical Union 1996