During Polar Sunrise Experiment 1992 at Alert in the Canadian high Arctic, size‐fractionated observations of aerosol constituents (halogens, Na, V, As, Sb, Zn, Al, Ca, SO4=, Sm, K, Mn, and Mg) were made using a low‐pressure cascade impactor and a high‐volume virtual impactor (HVVI). Over 80% of the mass of V, Br, I, As, Sb, Zn, and SO4= was in particles <2.5 μm diameter. In contrast to SO4=, NO3− has more mass in larger particles. Similarly, Cl peaked in larger particles (1.72 to 6.0 μm) than Na (0.49 and 1.72 μr). Both of these effects are likely caused by reactions of sulphate acids with salts of nitrates and chloride in submicrometer particles and the volatilization of HNO3 and HCl. For fine particles (diameter <2.5 μm), observations of relatively, nonvolatile primary particulate elements (Na, V, Mn) with the two measurement devices agreed within analytical uncertainty. In contrast, they did not agree well for the more volatile halogens. The HVVI always recorded higher. Sea‐salt enrichment factors of Cl (EFs s) referenced to Na for the HVVI data showed enrichment (1.2 to 1.8) in both fine and coarse aerosols during January. Thereafter, EFss averaged 0.92 and 0.57 for coarse and fine fractions, respectively, and were well correlated with each other. In contrast, EFss on fine particles collected with the cascade impactor were considerably lower (0.18 to 0.44), indicating volatilization of Cl within the device. A principal component analysis of fine particle (<2.5 μm) constituents from the HVVI identified six aerosol components consisting of anthropogenic (Mn, As, Sb, V, Zn, Al), sea salt (Cl, Na), iodine‐bromine (I, Br), photochemical (Br, −O3), soil (Ca, Al), and one loaded solely by Sm. For the whole period, there was a strong anticorrelation between O3 and aerosol Br but not with the other halogens. In this study, iodine was significantly linearly correlated with the square root of the Br concentration. It showed a weak anticorrelation with O3 only after polar sunrise but not before.

Measurements of particle number and mass size distributions of the atmospheric aerosol in the lower troposphere were made during the Polar Sunrise Experiment from January 20 to April 20, 1992, at Alert, Canada (82.5°N, 62.3°W). Particle number concentrations were determined by means of laser scattering particle counters and ranged from 50 to 600 cm−3 in the accumulation mode. Particle mass size distributions were measured using a Berner low‐pressure impactor; the total suspended particle mass ranged from 2.4 to 8.6 μg m−3. Average densities of (1.52±0.07) and (2.58±0.48) g cm−3 were calculated for accumulation and coarse mode particles, respectively, by combining impactor and optical size distributions. Boundary layer ozone concentrations were positively correlated with particles of diameters less than 0.35 μm and negatively with particles larger than 0.35 μm. Particles in the size range 6–12μm were detected exclusively during low ozone episodes.

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).

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