AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Emissions of Ice Nucleating Particles from Agricultural Lands
THOMAS HILL, Kaitlyn J. Suski, Ezra Levin, Anthony Prenni, Elvin Garcia, Sonia Kreidenweis, Paul DeMott, Colorado State University
Abstract Number: 455 Working Group: Primary and Secondary Aerosols from Agricultural Operations
Abstract Agricultural landscapes and farming activities (plowing, harvesting and burning) are strong potential sources of ice nucleating particles (INP). Those reaching cloud altitudes may modify precipitation formation processes and impact the transfer of solar and thermal energy through them. To define the numbers and compositions of INP emitted by these anthropogenically-transformed landscapes, we sampled representative western U.S agricultural regions, including at the Southern Great Plains DOE-ARM site (OK), an organic farm (CO), and during the harvesting of corn, sorghum, soybean and wheat (NE and KS). Real-time measurements of INPs were made using a continuous flow diffusion chamber (CFDC), and fluorescent biological particles were profiled using a Wideband Integrated Bioaerosol Sensor (WIBS-4A). INP concentrations were also measured via immersion freezing of filtered aerosols in an ice spectrometer, and characterized chemically, biochemically and biologically by their sensitivities to heat, hydrogen peroxide and enzymatic digestions, and DNA profiling. Boundary layer INP ranged from <0.005 to ~1 per L at -12°C, and 0.1 to 20 per L air at -20°C. Heat sensitivity tests conducted in real-time and on filtered aerosols revealed an often high proportion of organic INP in air above these lands. Harvesting generated INP-enriched plumes of pulverized plant tissue and soil dust. Since most crops support substantial populations of ice nucleation active (INA) bacteria, harvesting provides an effective means for their emission en masse. Next-generation profiling of bacteria in the aerosol downwind of corn harvesting showed that 20% of all bacteria were potential INA species of Pseudomonas and Pantoea, and quantitative PCR and sequencing of the ina gene (coding for the ice-active protein) confirmed that INA Pantoea agglomerans (11% of all bacteria in the aerosol) was abundant both in the aerosol and on the crop. Unexpectedly, post-harvest fields continued to emit INP at raised levels due to re-suspension of surface material.