Harmful Cyanobacterial Aerosolization Dynamics in the Airshed of a Eutrophic Estuary

HALEY E. PLAAS, Ryan Paerl, Karsten Baumann, Nathan S. Hall, Colleen Karl, Kimberly Popendorf, Malcolm A. Barnard, Naomi Chang, Nathaniel Curtis, Hwa Huang, Olivia Mathieson, Joel Sanchez, Daniela Maizel, Amy Bartenfelder, Jeremy Braddy, Karen Rossignol, Randolph Sloup, Hans W. Paerl, UNC Chapel Hill

     Abstract Number: 208
     Working Group: Aerosol Sources and Constituents of Emerging Importance and Their Impacts across Spatial Scales

Abstract
In addition to obvious negative effects on water quality, recent work suggests that harmful cyanobacterial blooms (CHABs) impact air quality via emissions of cyanobacterial cells, cyanotoxins, and other emerging biogenic compounds. Several toxigenic cyanobacterial genera and cyanotoxins have been detected in aerosol, but the associated environmental controls and human exposure risks remain largely unknown. Accordingly, this study aimed to 1) investigate the occurrence of microcystin (MC) and cyanobacterial communities in PM_2.5, 2) elucidate environmental conditions promoting their aerosolization, and 3) evaluate other apparent associations between CHABs and regional air quality in the airshed of the Chowan River, a eutrophic estuarine system in eastern North Carolina impacted by recurring CHABs. In summer 2020, during peak CHAB season, continuous PM_2.5 samples and interval water samples were collected for targeted analyses of cyanobacterial community composition and MC concentrations. Supporting air and water quality measurements were made in parallel to contextualize findings and permit statistical analyses of environmental factors driving changes in key aerosol outcomes. Several aquatic CHAB genera which were genetically traced to water samples were identified in PM_2.5, including Anabaena, Aphanizomenon, Dolichospermum, Microcystis, Pseudanabaena, and Tolypothrix. Specific Microcystis populations exhibited higher relative aerosolization factors (r-AF) compared to other cyanobacteria, but this observation was not statistically significant due to high variability between sampling periods (average r-AF = 2.5 ± 4.07). MC production was low throughout the study, but a mixed assemblage CHAB dominated by Dolichospermum occurred from late-June to mid-July. In association with the CHAB, the median PM_2.5 mass concentration increased to 10.5 µg m^-3 (IQR = 4.55), significantly above the non-bloom background of 5.81 µg m^-3 (IQR = 5.48) (W = 1465, p < 0.001). Results underscore the need to better investigate the role that freshwater harmful algal blooms, specifically HABs, play in regional air quality and subsequent respiratory health risk.