Review of Recent Developments and Shortcomings in the Characterization of Potential Atmospheric Ice Nuclei: Focus on the Tropics

Novel aerosol analysis approach for characterization of nanoparticulate matter in snow

Tropospheric aerosols are involved in several key atmospheric processes: from ice nucleation, cloud formation, and precipitation to weather and climate. The impact of aerosols on these atmospheric processes depends on the chemical and physical characteristics of aerosol particles, and these characteristics are still largely uncertain. In this study, we developed a system for processing and aerosolization of melted snow in particle-free air, coupled with a real-time measurement of aerosol size distributions. The newly developed technique involves bringing snow-borne particles into an airborne state, which enables application of high-resolution aerosol analysis and sampling techniques. This novel analytical approach was compared to a variety of complementary existing analytical methods as applied for characterization of snow samples from remote sites in Alert (Canada) and Barrow (USA), as well as urban Montreal (Canada). The dry aerosol measurements indicated a higher abundance of particles of all sizes, and the 30 nm size dominated in aerosol size distributions for the Montreal samples, closely followed by Barrow, with about 30% fewer 30 nm particles, and about four times lower 30 nm particle abundance in Alert samples, where 15 nm particles were most abundant instead. The aerosolization technique, used together with nanoparticle tracking analysis and electron microscopy, allowed measurement of a wide size range of snow-borne particles in various environmental snow samples. Here, we discuss the application of the new technique to achieve better physicochemical understanding of atmospheric and snow processes. The results showed high sensitivity and reduction of particle aggregation, as well as the ability to measure a high-resolution snow-borne particle size distribution, including nanoparticulate matter in the range of 10 to 100 nm.