Quantification of Bioaerosol Emission Flux Over a Semi-Arid Grassland

LILLIAN JONES, Rutambhara Joshi, Kevin Barry, Thomas Hill, Jay Ham, Sonia Kreidenweis, Delphine K. Farmer, Colorado State University

     Abstract Number: 110
     Working Group: Bioaerosols

Abstract
Understanding the rates of exchange (flux) of particulate matter between Earth’s surface and the atmosphere is essential to determining global aerosol loading, but there is a significant deficit of quantitative particle flux estimates, particularly for bioaerosols. Bioaerosol fluxes may be estimated by measuring (1) the vertical gradients in bioaerosol concentration and a scalar property and (2) a direct flux of that scalar. In this case, we measure airborne DNA as the bioaerosol tracer and temperature and sensible heat flux as the scalar and associated flux. This study seeks to determine the magnitude of DNA fluxes using the modified Bowen ratio method, and to understand the seasonal and meteorological dynamics of DNA flux between the semi-arid grassland and the atmosphere. A pilot study in October of 2023 established a methodology and confirmed the feasibility of such a measurement. We took thirty uniform flux measurements in the spring, summer, and fall of 2024 and the winter of 2025 to produce a robust dataset that reflects the potential seasonality of bioaerosol flux. The flux results thus far have been generally positive in value, indicating that the grassland may be emitting bioaerosols into the atmosphere. In the spring, fluxes ranged from -98.4 to 1,054 pg DNA m^-2 s^-1 with a median flux of 25.7 pg m^-2 s^-1; in the fall, fluxes ranged from -95.0 to 88.1 pg m^-2 s^-1 with a median flux of 17.6 pg m^-2 s^-1. The lower median flux and smaller range of fluxes in the fall as compared to the spring suggest potential seasonality of DNA emissions. This data will provide insight into the mechanisms of bioaerosol emission, enable the modeling of aerobiome dynamics, and decrease uncertainty in bioaerosol abundance in the atmosphere.