Concentrations, composition, and sources of ice-nucleating particles in the Canadian High Arctic during spring 2016.

Modelling studies suggest that the climate and the hydrological cycle are sensitive to the concentrations of ice-nucleating particles (INPs). However, the concentrations, composition, and sources of INPs in the atmosphere remain uncertain. Here we report daily concentrations of INPs and tracers of mineral dust (Al, Fe, Ti, and Mn), sea spray aerosol (Na⁺ and Cl^-), and anthropogenic aerosol (Zn, Pb, NO₃^-, NH₄⁺, and non-sea-salt SO₄^2-) at Alert, Canada during a three-week campaign in March 2016. The average INP concentrations measured in the immersion freezing mode were approximately 0.005 ± 0.002 L^-1, 0.020 ± 0.004 L^-1, and 0.186 ± 0.040 L^-1 at -15 ºC, -20 ºC, and -25 ºC, respectively. These concentrations are within the range of concentrations measured previously in the Arctic at ground level or sea level. Mineral dust tracers all correlated with INPs at -25 ºC (correlation coefficient, R, ranged from 0.70 to 0.76), suggesting that mineral dust was a major contributor to the INP population. Particle dispersion modelling suggests that the source of the mineral dust may have been the long-range transported dust from the Gobi desert. Sea spray tracers were anti-correlated with INPs at -25 ºC (R = -0.56). In addition, INP concentrations at -25 ºC divided by mass concentrations of aluminum were anti-correlated with sea spray tracers (R = -0.51 and -0.55 for Na⁺ and Cl^-, respectively), suggesting that the components of sea spray aerosol suppressed the ice-nucleating ability of mineral dust in the immersion freezing mode. Correlations between INPs and anthropogenic aerosol tracers were not statistically significant. These results will improve our understanding of INPs in the Arctic during spring. [ABSTRACT FROM AUTHOR]