A Hazy Shade of Winter: The Effects of Snow Cover on Dry Deposition in Two Experimental Forests

Dry deposition of particulate matter varies strongly within a given ecosystem depending on seasonal changes. One important seasonal transition is the addition of snow to the ground and canopy surfaces during the winter. Snow and ice cover are known to significantly depress the particle deposition velocity compared to observations for a dry canopy. Environments with snow and ice cover have near surface gradients in temperature and water vapor that have strong effects on particle movement towards collecting surfaces. By strengthening these gradients, the addition of snow cover has the potential to fundamentally change the surface properties of an ecosystem. Comparisons between deposition velocities for terrestrial surfaces and snow- and ice-covered surfaces often depend on measurements for two separate ecosystems, and there are few observations for the impact of snow cover within a given ecosystem. Here we examine eddy-covariance flux measurements to explore the direct effects of snow cover on dry deposition within an ecosystem. This work reports aerosol flux and deposition velocities as they change with the addition of snow cover at two sites: Manitou Experimental Forest in Colorado (2015 - 2016) and the Glacier Lakes Ecosystem Experiments Site in Wyoming (2020). We further compare the transitions for the two measurement sites to explore the uniformity of snow effects across different ecosystems.