Articles | Volume 18, issue 18
Research article
28 Sep 2018
Research article |  | 28 Sep 2018

Agricultural harvesting emissions of ice-nucleating particles

Kaitlyn J. Suski, Tom C. J. Hill, Ezra J. T. Levin, Anna Miller, Paul J. DeMott, and Sonia M. Kreidenweis

Abstract. Agricultural activities can modify natural ecosystems and change the nature of the aerosols emitted from those landscapes. The harvesting of crops can loft plant fragments and soil dust into the atmosphere that can travel long distances and interact with clouds far from their sources. In this way harvesting may contribute substantially to ice-nucleating particle (INP) concentrations, especially in regions where agriculture makes up a large percentage of land use. However, a full characterization of particles emitted during harvesting has not been reported. This study characterizes immersion mode INPs emitted during harvesting of several crops in the High Plains region of the United States. The Colorado State University Continuous Flow Diffusion Chamber (CFDC) and the Ice Spectrometer (IS) were utilized to measure INP concentrations during active harvesting of four crops in Kansas and Wyoming. Large spikes of INPs were observed during harvesting, with concentrations over 200 L−1 at −30 °C measured during a wheat harvest. To differentiate between mineral and organic components, a novel heating tube method was employed in real time upstream of the CFDC to deactivate organic INPs in situ. The results indicate that harvesting produces a complex mixture of organic, soil dust, and mineral components that varies for different crops. Electron microscopy analysis showed that while mineral components made up a large proportion of INPs, organic components comprised over 40 % of measured INPs for certain crops at warm temperatures. Heating and enzyme post-treatment of aerosol samples collected for IS processing indicated that bacteria and heat-labile and heat-stable organics contributed to wheat harvest-produced INPs. These results indicate that plant material and organic particles are a significant component of harvest INPs and their impacts on ice formation in clouds and precipitation on a regional scale should be explored.

Short summary
The harvesting of crops emits large amounts of particles into the air. These particles can form and interact with clouds to alter cloud properties and precipitation, but the magnitude of these effects is unknown. This study looked at the ability of harvest particles to form ice in clouds by sampling with an ice nucleation chamber downwind of fields being harvested. Some crops emitted large amounts of ice-nucleating particles, and harvest emissions are mixtures of organics, soil, and minerals.
Final-revised paper