Marine Submicron Aerosols from the Gulf of Mexico: Polluted and Acidic with Rapid Production of Sulfate and Organosulfates

SHAN ZHOU, Fangzhou Guo, Subin Yoon, Sergio Alvarez, Sujan Shrestha, James Flynn, Sascha Usenko, Rebecca J. Sheesley, Robert Griffin, Rice University

     Abstract Number: 516
     Working Group: Remote and Regional Atmospheric Aerosol

Abstract
The Texas Gulf Coast experiences persistent air quality problems including elevated particulate matter (PM) concentrations. However, few studies have investigated the impact of air masses transported from the Gulf of Mexico. We made real-time measurements at a beachfront site in Corpus Christi, Texas, from April 2 – 22, 2021, using a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) to characterize the “background” aerosol chemical composition advecting into Texas and the factors controlling this composition. The average (±1σ) concentration of submicron aerosol (PM₁) during the sampling period was 15.6 (± 9.8) µg m^-3, with the maximum reaching nearly 100 µg m^-3. Sulfate was the most abundant component, on average accounting for 46% of total PM₁ mass, followed by organics (39%). Air masses arriving at the sampling site were frequently (58% of the sampling period) directly from the Gulf with negligible contact with land over the previous two days. The marine “background” aerosols from the Gulf shared similar characteristics with marine aerosols previously observed at other locations in the world, in that they had high sulfate content and appeared to be very acidic and aged. However, Gulf marine “background” aerosols were polluted; the average non-refractory PM₁ mass concentration (14.9 ± 10.0 µg m-3) was higher by a factor ranging from 3 to 70 compared to marine aerosols at other locations. Our analysis showed that anthropogenic shipping emissions over the Gulf of Mexico explain 78.3% of the total measured “background” sulfate in the Gulf air. Rapid growth of sulfate and acidic-oxygenated organic aerosol (acidic-OOA), an OA factor identified by positive matrix factorization analysis of the HR-ToF-AMS data, were observed during a two-day haze episode. Further analysis suggests that aqueous oxidation of ship emissions by organic peroxides in the particles might have been an important formation pathway for the sulfate-dominant haze episode.