Biogenic Volatile Organic Compounds from Pennsylvanian Lakes Sampled during the 2024 Algal Bloom Season

Biogenic volatile organic compounds (BVOCs) emitted from aquatic systems are increasingly recognized for their influence on atmospheric chemistry. However, emissions from freshwater environments, specifically during harmful algal bloom (HAB) events, remain poorly quantified. These HAB events are increasing globally in frequency and intensity, driven by climate change, nutrient runoff, and land-use changes. This study investigates the water-to-air gas exchange rates of BVOCs from southwestern Pennsylvanian freshwater lakes during peak HAB conditions, with a focus on nitrogen-containing compounds that are typically underrepresented in atmospheric measurements. Using atmospheric pressure, hydronium chemical ionization mass spectrometry (CIMS), we measured BVOC emissions from 18 lake samples in the laboratory, capturing real-time fluxes of 900 unique masses. Ammonia, pyrroline, and pyridine consistently exhibited the highest emission fluxes across samples. Alkylamines were less abundant, although they remain atmospherically important due to their role in new particle formation. These results represent the first reported real-time freshwater flux measurements of alkylamines, pyrroline, and pyridine, offering new insight into the atmospheric implications of HABs. Notably, no clear correlation was observed between BVOC fluxes and chlorophyll <i>a</i> and phycocyanin concentrations, which were taken to represent the cyanobacterial concentrations in the samples. This suggests that emissions are influenced by other biological or chemical factors not captured in this study. Principal component analysis identified two significant outlier water samples, driven by elevated ammonia, pyrroline, and an unknown compound at 124.101 amu, though the underlying cause of these deviations remains unresolved. The remaining lake emissions were similar. These findings provide foundational observations to better understand the role of freshwater system emissions in regional air quality and atmospheric processes.