Secondary Organic Aerosol Formation from Cyanobacterial-Derived Volatile Organic Compounds

Recent work has demonstrated the primary aerosolization of cyanobacterial cells, toxins, and metabolites from cyanobacterial harmful algal blooms (CHABs). However, another possible source of CHAB-derived aerosols is secondary organic aerosol (SOA) formation via the atmospheric oxidation of volatile organic compounds (VOCs) emitted by CHABs. To examine potential SOA formation from CHABs, two cyanobacterial VOCs─2-methylisoborneol (2-MIB) and geosmin (GSM)─were oxidized via hydroxyl radicals (^•OH) in a potential aerosol mass-oxidation flow reactor. At 100 ppbv, SOA mass yields were 15.1 ± 2% and 33.9 ± 1.3%, from 2-MIB and GSM, respectively. SOA mass concentrations generated from 2-MIB and GSM oxidations reached up to 102 ± 22 μg m^-3 and 252 ± 52 μg m^-3, respectively, when exposed to 8-16 days of equivalent ^•OH exposure. Offline molecular-level characterization of Teflon-filter collected SOA by reverse-phase liquid chromatography interfaced to high-resolution quadrupole time-of-flight mass spectrometry equipped with electrospray ionization (RPLC/ESI-HR-QTOFMS) revealed 7 distinct chemical compounds in both 2-MIB and GSM-derived SOA, which we propose for use as molecular tracers of CHAB-derived SOA in ambient fine particulate matter (PM_2.5). Two 2-MIB-derived SOA tracers (molecular formulas of C₁₀H₁₈O₄ and C₁₀H₁₆O₅) were measured in PM_2.5 collected from the airshed of a CHAB. To the best of our knowledge, this is the first observation of respirable CHAB-derived SOA. Our findings strengthen the need to consider outcomes related to human respiratory health in risk assessments and public health messaging surrounding residential and recreational exposures to CHABs.