Aircraft lidar studies of the Arctic haze and their meteorological interpretation

Abstract

The results of aircraft lidar studies of the Arctic haze are reported. These studies were conducted in 1993–1994 during a Russian-German Arctic mission. The first priority was given to measuring the scattering and depolarization coefficients of troposperic aerosol at 0.53 μm wavelength. Measurements were made along vertical and horizontal paths at board an I1-18 aircraft at altitudes ranging from 150 to 8,800 m in various regions of the Arctic. In winter, under cloudless conditions, layers with scattering coefficients exceeding 3 ∗ 10 −5 m −1 were observed in the Canadian, Russian and Atlantic sectors of the Arctic. These layers were classified as Arctic haze. Haze layers sometimes filled 11 to 43% of the vertical column, alternating with ‘clean’ layers in which scattering coefficients were 10 to 100 times less. According to thermodynamical analysis of the arriving air masses, they could have been polluted from ground sources either in very dry areas (with surface relative humidity less than 20%) or in areas with temperatures and humidities close to those observed in industrial regions of the Western and Eastern Europe and eastern North America. In the latter case, however, on their way to the Arctic the airmasses had to undergo condensation. This was consistent with the rate of pollution scavanging by clouds and precipitation, if only scavanging efficiency was the lowest.