Identification of potential primary biological particle emissions and rupture events at the Southern Great Plains ARM site

Abstract:

Primary biological aerosol particles (PBAP) are emitted directly from biological processes in the terrestrial biosphere, including viruses, bacteria, fungi, pollen, and other plant matter. We use a suite of observational data from extensive aerosol measurements at the Department of Energy (DoE) Atmospheric Radiation Measurements (ARM) United States Southern Great Plains (SGP) site, to understand the occurrence of two types of PBAP from the land surface: pollen and fungal spores. For pollen, long-term measurements at two urban counting stations near the DoE SGP site and pollen show two distinct time periods with high total pollen counts (late winter/early spring day 50-120) and late summer (day 250-300). The Lidar vertical profiles of aerosol loading at SGP during 2011-2015 shows that the days having the near surface daily linear particle depolarization ratio > 0.1 are coincident with predominance of total organics based on the ACSM chemical composition data, suggesting the presence of primary pollen emissions. In total, ~10% of these days are identified as potential pollen event days, most of which occur during the two pollen event periods. During potential pollen event days with high humidity (>80%), the aerosol size distribution observation shows enhancement of the particles having diameter < 1µm, which is an indicator of pollen rupture events thus releasing the sub pollen particles. For fungal spores, local counts suggest two distinct time periods with high total fungal spores counts: late spring/early summer (day 100-195) and late summer/autumn (day 220- 340). Based on the size distributions of observed fungal spore rupture events at the site, we find that ~8% of the days during 2011-2013 have higher aerosol number count specifically over the range of the fungal spore’s mobility diameter (20-50 nm). These potential fungal spore rupture events generally fall within the seasonal observed peak fungal emissions. While short-lived (e.g., a few minutes to hours), these potential fungal spore rupture events occur within the rainfall time period or after a prolonged period of exposure to rainfall for more than 10hrs. Taken together, we identify that PBAP primary emissions and rupture events occur about 4-33 days per year, representing an important component of the aerosol budget during seasonal emission periods.