Light Absorption at Near-Infrared Wavelengths by Organosulfate Aerosols
AUGUST LI, Joshin Kumar, Joseph V. Puthussery, Nurun Nahar Lata, Gregory W. Vandergrift, Zezhen Cheng, Felipe Rivera-Adorno, Valerie Viteri, Benjamin Sumlin, Ganesh Chelluboyina, Alexander Laskin, Swarup China, Rajan K. Chakrabarty,
Washington University in St. Louis Abstract Number: 514
Working Group: Carbonaceous Aerosol
AbstractOrganosulfate (OS) aerosols are an important contributor to the secondary organic aerosol mass burden over the continental United States. While OS chemical properties and formation pathways have been extensively studied, knowledge of their optical properties remains elusive. Here, we investigated the spectral optical properties of ambient OS particles at a coastal industrial site in La Porte, Texas, as part of the Department of Energy’s TRacking Aerosol Convection interactions ExpeRiment (TRACER) field campaign during July and August 2022.
Aerosol absorption and scattering coefficients were measured in real time using custom-built integrated photoacoustic nephelometer spectrometers, which operated at 405, 721, and 1047 nm. Synchronous filter sampling of particles was performed and subsequently analyzed for particle-resolved composition using computer-controlled scanning electron microscopy. Based on approximately 15,000 particles analyzed, we identified two distinct periods of OS loadings: one where OS comprised 28% of the total particles (“OS dominant”), and one where OS was largely a background contributor (12%; “OS background”).
The airmass corresponding to the OS dominant period originated from the Houston shipping channel and marine emissions. This period was characterized by an average absorption coefficient (B
abs) of 7.98 Mm
-1 and single scattering albedo (SSA) of 0.71 at 405 nm. At 1047 nm, OS particles contributed to 36% of aerosol absorption, with the remaining fraction attributed to black carbon. The OS particles resisted morphological distortion when heated to 450 °C under atmospheric pressure, indicative of their low volatilities. By comparison, the OS background period showed a relatively lower B
abs of 6.41 Mm
-1 and a higher SSA of 0.83 at 405 nm. During this period, the OS contribution to 1047-nm light absorption was 17%. Collectively, our results suggest that increasing OS abundance is associated with reductions in SSA due to higher absorption and lower scattering at near-UV wavelengths and enhancements in light absorption at near-IR wavelengths. OS aerosols could be significant contributors to shortwave forcing in regions dominated by shipping and chemical refinery emissions.