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Wet cooling towers evaporate water to transfer waste heat to the environment. In the process, they also emit liquid water in the form of spray drift. These emissions dry in the atmosphere to form aerosol particles composed of impurities in the water. Emission factor guidance for cooling towers is provided by EPA AP42. Total emissions are a combination of spray drift and ambient aerosol passing through the tower. Net emissions take into account the scrubbing of ambient particles in the tower. We directly measured tower particulate emissions and ambient concentrations to determine the contribution of spray drift to tower emissions as well as scrubbing effect on ambient particles. Two companion papers describe the instrumentation and the spray drift measurements. Copyright © 2025 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]

Wet cooling towers are used in industrial processes, power plants, and heating, ventilation, and air conditioning systems. Their purpose is to reject waste heat from a system through evaporative cooling of process water. Due to their design, a small fraction of process water is emitted from the tower exit, termed "spray drift." Dissolved solids contained within spray drift droplets are regulated as PM10 emissions by EPA AP-42. Here, we use a novel instrumentation package to measure particulate emissions from drift droplets at two cooling towers located at separate power plants. We find that drift droplet properties depend on the sampling position over the tower so multiple positions need to be sampled to accurately estimate emissions. We estimate 11 and 3.3 grams of PM10 are emitted from each tower per hour, with 78% and 87% of PM10 emissions also qualifying as PM2.5. AP-42 overestimates PM10 emissions by a factor of 2.4 for one tower and nearly 300 for the other. These results suggest that AP-42 may require revision to both accurately reflect lower PM10 emissions and account for unregulated PM2.5, which constitute the majority of emissions. Copyright © 2022 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]