Received: 07 Oct 2020 – Accepted for review: 16 Nov 2020 – Discussion started: 20 Nov 2020
Abstract. This study presents a comprehensive investigation of ice-nucleating particles (INPs) in the surface materials and aerosol particles from U.S. cattle feeding facilities. Using a modern suite of online and offline aerosol particle characterization instruments, we conducted a three-year field survey (2016–2019), Aerosol Interaction and Dynamics in the Atmosphere (AIDA) cloud chamber experiments, and ice crystal residual (ICR) analyses for the feedlot sample. Our results showed unique supermicron size dominance in the feedlot INPs with a high concentration of INPs (several hundred and thousand INPs L−1 at −20 °C and −25 °C, respectively). Thus, agricultural fields, especially animal feeding facilities, represent important INP sources if these particles rise to sufficient height in the atmosphere. New data on the ice nucleation (IN) properties of agricultural dust at heterogeneous freezing temperatures (Ts > −29 °C) were generated, providing statistical context. Overall, we successfully characterized physical, chemical, and biological properties of aerosol particles found at a cattle feedlot, thereby finding their unique heat-tolerant nature. The relationship between these measured properties and atmospheric IN parameterization relevant to mixed-phase clouds is discussed. Our INP parameterization and ICR characterization are meaningful for improved understanding of INP emission and cloud microphysical processes in the supermicron-particle laden region. These unique INPs may directly influence the lifetime of supercooled clouds in a unique manner for this region. An application of our IN parameterization is crucial to explore INP relations to supercooled cloud properties over such a predominant agricultural area.
This study presents that feedlot could be a constant source of atmospheric ice particles, which influence clouds, precipitation, and climate. About 50 % of feedlot ice particles were supermicron in diameter. They were heat tolerant and may be an important part of a regional aerosol-cloud interaction. Feedlot ice residuals were rich in organics and low in salts. No notable known ice-nucleating microorganisms were found in our feedlot samples. Their ice nucleation parameterization is provided.
This study presents that feedlot could be a constant source of atmospheric ice particles, which...