Summer aerosol profiles over Algonquin Park, Canada

Abstract

During the summer of 1982, daytime vertical profiles of aerosol particle concentrations and state parameters in the lower troposphere were measured from a Twin Otter aircraft flying over Algonquin Park, Canada. Particles from 0.2 to 30 μm diameter were counted and sized with PMS ASASP and FSSP wingmounted probes. When 48-h back trajectories at 850 mb were from the south, the mean aerosol particle concentrations were approximately 2000cm −3 at 950mb (near ground level), and decreased with height rapidly until 750 mb. When trajectories were from the west and north, the 950 mb concentrations were much lower but relatively uniform to 800 mb. Individual profiles showed that maxima could occur near cloud base. Average number, area and volume spectra of the subμm aerosol have been determined for 700 and 900 mb and show a maximum near 0.2–0.3 μm with volume-weighted geometric mean diameters near 0.3 μm. Spectra of particles larger than 2 μm indicate a second maximum at about 10 μm diameter. Ground-based chemistry measurements show that most of the subμm aerosol particles of southern origin were formed principally from water soluble sulphate compounds. Based on the measurements made during southerly winds, radiation calculations predict visibilities of appproximately 10 km and suggest that particle absorption could result in a 2–4°C temperature increase in the atmospheric layer below 2 km.