Observations of the Gas Phase Composition of the 2024 BioLab Industrial Plume in the Atlanta Metropolitan Area

A fire at a pool chemical manufacturing facility in Conyers, Georgia, on September 29, 2024, released a persistent chemical plume that impacted the Atlanta metropolitan area, causing evacuation of more than 17,000 people. We used chemical ionization mass spectrometry (HR-TOF-CIMS) in Midtown Atlanta (21 miles from the facility), and in Conyers (quadrupole CIMS) to characterize plume composition. We observed unexpectedly high concentrations of Br2 (up to 1.4 × 102 ppbv) dominating early plumes, along with elevated levels of HNCO (31 ppbv) and numerous other compounds. Twenty-six species were identified, including reactive nitrogen-containing compounds (e.g., HNCO, cyanoacetic acid, and cyanamide) and oxygenated volatile organic compounds (e.g., acetaldehyde). Br2 concentrations in Midtown exceeded United States Environmental Protection Agency (EPA) 1 h Acute Exposure Guideline Levels (AEGL-1) thresholds by a factor of 4. Later measurements in Conyers showed Cl2 reaching 3.7 × 102 ppbv during the second week. Given that Midtown observations were 21 miles downwind, concentrations near the source in Conyers were likely 2 orders of magnitude higher. This is the first comprehensive chemical characterization of a pool chemical decomposition plume revealing complexity beyond simple halogen release and highlighting health risks from simultaneous exposure to multiple respiratory irritants.