AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
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The Cytotoxicity of Brown Carbon and its Dependence on Combustion Conditions and Light Absorption Properties
KHAIRALLAH ATWI, Arnab Mondal, Jitendra Pant, Zezhen Cheng, Omar El Hajj, Hitesh Handa, Rawad Saleh, University of Georgia
Abstract Number: 853 Working Group: Biomass Combustion: Emissions, Chemistry, Air Quality, Climate, and Human Health
Abstract A large fraction of the organic aerosols emitted from incomplete combustion is light absorbing (henceforth called brown carbon, or BrC). We have previously shown that combustion BrC exhibits a continuum of light-absorption properties that are correlated with the combustion conditions [Saleh et al. (2018) ESTL 5, 8, 508-513]. Here, we build on these findings to investigate the dependence of BrC toxicity on combustion conditions. We used toluene as a model fuel and finely controlled the combustion temperatures and air-to-fuel ratios to produce BrC of different degrees of light absorption, described by the imaginary part of the index of refraction at 550 nm (k550). We collected 3 BrC samples that we categorized as light (k550 = 0.001), medium (k550 = 0.05), and dark (k550 = 0.1). We then analyzed the samples in vitro for their cytotoxicity towards human lung epithelial cells. The procedure involved exposing the cells to 9 doses of each of the BrC samples to determine the dose-dependent cell viability with respect to controls (cells without BrC exposure). We found that the light BrC was cytotoxic (viability < 80%) starting at a dose of 3.7 μg/cm2, while at a dose of 31.2 μg/ cm2, most cells did not survive, (viability <10%). The medium BrC was only cytotoxic at the highest concentration, 312.5 μg/ cm2 (viability <60%). The dark BrC was not cytotoxic at any dose (viability always >80%). These results suggest that the light BrC emitted from the less efficient combustion, which is typically associated with smoldering combustion conditions, is more harmful to health.