Abstract View
Pollen as a Source of Atmospheric Particles and Ice Nucleating Particles
BRIANNA HENDRICKSON, Alyssa Alsante, Sarah Brooks, Texas A&M University
Abstract Number: 236
Working Group: Bioaerosols
Abstract
Annual emissions of primary biological aerosol particles (PBAPs) contribute 10-1,000 Tg to the aerosol population. With pollen acting as a substantial fraction of annual PBAP emissions (47-84 Tg), it is important to accurately quantify pollen emissions. Whole pollen grains are released from plants and rupture during pollen season, releasing pollen grain fragments referred to as subpollen particles (SPPs). Whole pollen grains and SPPs can act as ice nucleating particles (INP) influencing cloud formation and precipitation. Accurate characterization of meteorological conditions required for pollen emissions to occur is needed to quantify the contribution of pollen to the aerosol population. This study is an evaluation of various mechanisms (conventional relative humidity and wind versus wind only) to determine the threshold parameters needed for live oak pollen grain rupture in a laboratory chamber. To represent the conventional mechanism, branches were exposed to high relative humidity >95%, followed by reduced relative humidity (<80%) and winds (up to 4mph). In contrast, wind-only experiments were conducted by cycling fans on and off at constant relative humidity. While both conventional relative humidity cycling and lightning have been proposed as SPP production mechanisms, neither are essential elements of the production of the high concentrations of SPP as evidenced by concentrations as high as 2.4E+02 ± 1.3E+02 SPPs per cm3 observed in wind-only experiments here. In fact, the mean SPP emissions during relative humidity cycling was lower than that during wind-only with concentrations as high as 7.3E+01 ± 3.4E+01 SPPs per cm3. The concentration of SPPs generated from whole pollen grains was characterized and used to calculate SPP emission factors. Live oak SPP emission factors were determined to be between 1.4E+04 and 7.7E+04 SPPs per pollen grain, representing a significant source of cloud-forming aerosol. Concentrations and ice-nucleating behavior of pollen and SPP will be reported, and atmospheric implications discussed.