Assessing the Varied Sources of Ice Nucleating Particles from Soils and Their Atmospheric Abundances

Within the research field of ice nucleating particles (INPs), here taken to include any particle containing an ice nucleating element, understanding of the contributions of varied soils to atmospheric INPs has grown recently to acknowledge and support many years of evidence that mineral particles are not the sole entity of interest. Soils contain living organisms, decaying plant material, myriad forms of organic matter, and support plants that themselves contain material components and/or harbor organisms that are ice nucleation active. This paper describes recent studies to identify INPs from soils and land sources, and link these to the presence of similar INPs in the air over various ecosystems that range from high arid to more agriculturally-productive regions in the West-Central United States. In this effort, we utilize online and offline INP and bio-fluorescent particle measurements, online and offline thermal and enzymatic processing, and genetic analyses of aerosols, to characterize INPs from soils, plants, and in the air in the same regions. These measurements describe a common abundance (number concentrations) of biological INPs in air, especially during harvest operations. Additionally, arable soils are found to harbor large numbers of non-mineral INPs, which may be the same types found in air. We will also discuss efforts to improve confidence in measuring INP sources via multiple methods, using soils of varying organic matter content in the laboratory as test particles. In this regard, we will overview some results from recent inter-comparison studies including the second (laboratory) phase of the Fifth international Ice Nucleation workshop (FIN02) in which many methods were compared while sampling selected soil and other particles.