Ice Nucleating Particle Emissions from Natural and Agricultural Soils

The role of mineral dusts as sources of atmospheric ice nucleating particles (INPs) is well known. Nevertheless, laboratory research suggests that mineral dusts cannot explain the abundance of ice nucleating particles in the atmosphere at temperature warmer than -10 to -20°C. Herein we discuss measurements that demonstrate that arable soils possess varied biogenic INPs that include plant and soil microbes (and their cell-free INPs), plant fragments, pollen, lichen and unidentified organic INPs. Additionally, we report on sampling studies performed in the Central United States to investigate the presence and action of these organic INPs in the air above a range of relevant landscapes/ecosystems. We show through the use of thermal, chemical and enzymatic treatments to denature INPs that sources from arable lands that are active at temperatures warmer than -20°C are dominated by components that are probably proteinaceous (most active) as well as from a pool of stable organic materials, while mass-dominant mineral substances present a background contribution that is much less potent until lower temperatures. These sources are also identified in the air above the land in most cases, especially during region-wide, large scale perturbations such as harvesting. Mineral sources are found to dominate in cases where local emissions are limited, especially in natural landscapes such as sagebrush shrubland and semi-desert regions.