Effects of Atmospheric Aging on the Dithiothreitol-based Oxidative Potential of Carbonaceous Aerosols

KA YUEN CHEUNG, Jun Zhang, Tiantian Wang, Lisa Kattner, Sophie Bogler, Martin Gysel, Jay G. Slowik, Vishal Verma, André S. H. Prévôt, Imad El Haddad, David Bell, Robin Modini, Paul Scherrer Institute

     Abstract Number: 358
     Working Group: Health-Related Aerosols

Abstract
Carbonaceous aerosols are directly emitted into the atmosphere from a variety of sources (e.g. combustion processes) or formed from the atmospheric oxidation of biogenic or anthropogenic precursors, which account for a large fraction of particulate matter (PM) in the ambient. Atmospheric aging processes continue to alter the chemical and physical properties of carbonaceous aerosols, so does the oxidative potential (OP) which is a measure of their ability to generate reactive oxygen species (ROS). Understanding how aging processes affect the OP of different types of carbonaceous aerosols is therefore crucial for predicting their potential health effects in different regions and under different atmospheric conditions. Numerous smog chamber studies investigated the OP of carbonaceous aerosols from various sources or aging processes. However, large uncertainty remains and inconsistent results may be due to the lack of standardized protocol for OP measurement, which hindered the direct comparisons among studies.

In this study, we conducted smog chamber experiments to investigate the OP as a function of aging for carbonaceous aerosols from two complex emissions (i.e. residential wood burning and coal combustion) and two single-precursor systems (α-pinene-derived and naphthalene-derived secondary organic aerosols (SOA)). In particular, we broadly explore the changes in OP of carbonaceous aerosols from residential wood burning under a range of atmospheric aging processes including OH photochemical reaction, ozonolysis in the dark, and NO₃ nighttime oxidation. We measured the hourly OP with a semi-continuous system for dithiothreitol (DTT) assay, together with measurements by aerosol mass spectrometer (AMS), scanning mobility particle sizer (SMPS) and gas analyzers. These provided transient information for more in-depth comparisons of aerosol toxicity in terms of the intrinsic OP (OP_m^DTT) among different types of carbonaceous aerosols at a given equivalent aging time. Our results show that OH photochemistry could produce aerosols with high OP_m^DTT more rapidly than other oxidation pathways.