Aerosol optical properties over north central Canada during BOREAS

A network of five automated and two handheld solar radiometers were operated during the 1994 Boreal Ecosystem-Atmosphere Study (BOREAS) in northern Saskatchewan and Manitoba, Canada, in order to characterize the atmospheric aerosol optical properties. These data were collected to allow for atmospheric correction of optical remote sensing data in the visible to short-wave infrared spectrum (0.4 to 3 μm) and to characterize the aerosol climatology of the region. Aerosol optical thickness inferred from the direct solar irradiance measurement at the ground shows that the background conditions for the area are very clear in the absence of local aerosol sources with an aerosol optical thickness of ~0.1 at 500 nm. The northeastern portion of the BOREAS region was dominated by smoke from forest fires from early June to mid-September with values averaging above 1 at 500 nm in mid-July for extended periods. Size distributions derived from solar almucantar measurements show the predominance of small particles during smoke episodes when compared to that for background conditions. Measurements are continuing through 1995 to better characterize the climatology of aerosols and water vapor column abundance since the summer of 1994 was unusually warm and dry