Live oak pollen as a source of atmospheric particles

Pollen grains are released from plants and rupture, releasing pollen grain fragments referred to as subpollen particles (SPPs). This study is a laboratory evaluation of live oak, Quercus virginiana, to determine the environmental conditions needed to emit SPPs and measure the concentration of SPPs produced. To represent conventional SPP release, live oak branches were exposed to high relative humidity (> 95%), followed by reduced relative humidity (73.5%-76.3%) and wind (up to 1.8 m s⁻¹). In contrast, wind-driven SPP release experiments were conducted by exposing branches to constant relative humidity while cycling fans used to simulate winds. Wind-driven experiments produced maximum SPP concentrations as high as 3.3 × 10² ± 2.7 × 10² SPPs per cm³. The maximum SPP emissions during conventional SPP release experiments were as high as 7.3 × 10¹ ± 3.4 × 10¹ SPPs per cm³. The total number of SPPs emitted during conventional SPP release experiments was not significantly different from the SPP emissions during wind-driven SPP release experiments at a 5% significance level. The concentration of SPPs generated from pollen grains was used to calculate SPP emission factors. SPP emission factors were determined to be between 1.6 × 10⁴ and 9.0 × 10⁴ SPPs per pollen grain and between 4.7 × 10¹² and 2.2 × 10¹⁵ SPPs per m². These results indicate that SPPs represent a significant source of cloud-forming aerosol and have the ability to impact respiratory health.