Some Physical and Chemical Properties of the Arctic Winter Aerosol in Northeastern Canada

Abstract

Measurements spanning much of the particle size spectrum were made on the surface aerosol arriving at Igloolik, Northwest Territories, Canada during late February 1982. Vertical profiles of aerosol particle concentration were obtained during one day of the study period. Concentrations of Aitken nuclei and cloud condensation nuclei as well as the aerosol light-scattering coefficient were measured instrumentally several times a day. Inertial impaction systems were used to separate and collect particles for microscopic sizing and chemical analysis. Suspended and precipitating ice crystals were inertially collected on microscope slides. The aerosol observations were accompanied by observations of temperature, wind speed and direction, visibility and cloud type. An upper-air station at Hall Beach, <100 km from Igloolik, provided radiosonde data. Diurnal variations in the Aitken nucleus concentrations were observed on several clear days. The concentrations were frequently seen to follow the diurnal temperature variation, reaching a maximum near midday. Vertical profiles of Aitken nucleus concentrations obtained prior to and during one of these diurnal peaks suggests that this pattern was limited to the near-surface layer. Throughout the study, virtually all of the aerosol particle mass lay between 0.2 and 4.0 μm diameter. There was little indication of any diurnal change in the particle concentration in this size range. A clear difference in the quality of the air reaching Igloolik was detected on 23 February. Associated with this was a doubling of the particle concentration while the apparent particulate mass increased from ∼6 to ∼11 μg m−3. Impacted aerosol particles were found to be composed of 15–50% water soluble compounds before 23 February and 40-100% after this date. Sulfate was the dominant ionic species in all cases. Vertical profiles of the large aerosol particles, obtained with an airborne nephelometer, suggested a slightly enhanced concentration at the surface and a uniform concentration in the lower troposphere. Profiles of Aitken nucleus concentrations pointed to a surface source of small nuclei which diffused vertically and independently of the larger particles. Suspended ice crystals may have accounted for a significant portion of the degradation in visibility observed throughout the study.