Collaborative Research: Quantifying the Role of Pollen in Cloud Formation through Measurements and Modeling

Abstract

While pollen is emitted from the Earth's surface in large quantities from vegetation, these emissions are typically excluded from inventories due to the large size of pollen grains. However, recent studies have shown that pollen grains easily rupture when wet, forming smaller sub pollen particles (SPP); these SPP have not been well-studied. The central goal of this study is to accurately establish the amount of SPP produced by pollen rupture and to determine its cloud formation properties.

This study will include a series of experiments utilizing a plant chamber and atmospheric modeling simulations. The laboratory measurements will (1) Quantify the number of SPP emitted from a single pollen grain and from a plant under atmospheric conditions, (2) Determine the supersaturation required for cloud condensation nuclei (CCN) activation, and (3) Determine the temperatures and relative humidities required for ice nucleating particles (INP) activation. These results will provide critical input for an online pollen emissions model that will be used with the Weather Research and Forecasting model coupled with Chemistry model (WRF-Chem) to (1) Implement the pollen emission rupture mechanism in WRF-Chem, (2) Utilize measured rupture data to improve simulations of pollen rupture, and (3) Conduct new simulations that account for the indirect effects from both warm and cold clouds using CCN and INP activation measurements.

This interdisciplinary project uses laboratory and modeling components to maximize the value of the measurements for improving model estimates of pollen effects on cloud formation. The work will also be integrated in an undergraduate course that will introduce pollen sampling equipment and instruct students on the basics of aerosol and climate modeling.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.