Seasonal Variability, Sources, and Parameterization of Ice-Nucleating Particles in the Rocky Mountain Region During SAIL

RUICHEN ZHOU, Russell Perkins, Drew Juergensen, Kelton Ayars, Oren Dutton, Paul DeMott, Sonia Kreidenweis, Colorado State University

     Abstract Number: 436
     Working Group: Aerosols, Clouds and Climate

Abstract
The Surface Atmosphere Integrated Field Laboratory (SAIL) campaign was conducted in the Upper Colorado River Basin, a critical watershed supplying water to the western United States. Investigating atmospheric ice-nucleating particles (INPs) in this mountainous region is crucial for improving precipitation prediction in this area and reducing uncertainties in aerosol-cloud interactions in global climate models. Here, we present results from nearly two years of INP observations during SAIL. Clear seasonal variations were observed for INPs active at all temperatures, with concentrations lowest in winter, increasing in spring, peaking in summer, and decreasing in autumn. Aerosol source apportionment analysis found that dust in the coarse mode was strongly correlated with INPs, suggesting its dominant role. Further sample treatments with heating and H₂O₂ separated INPs into fractions of biological and heat-labile, other organic, and inorganic types. Other organic INPs were correlated with inorganic INPs with a ratio near 10, suggesting similar origins, and the abundant organic INPs indicate that soil dust is the main contributor to INPs in this region. Biological INP contributions were identified mostly during warm seasons, with limited contribution in winter. An unexpected correlation was found between biological and heat-labile INPs and other organic INPs at −15 ℃. This potentially provides an indirect approach for estimating biological INPs in this area. A parameterization method was developed based on the surface active site density for the two-year samples. This mainly represents the INP particles originating from soil dust and may be applicable to other remote continental areas where soil dust dominates INP populations.