Exploring Factors Influencing Sources and Distributions of Aromatics in an Arctic Winter Urban Environment

Aromatic hydrocarbons are hazardous air pollutants with high toxicity, but sources in cold urban Arctic winter environments are poorly understood. Surface observations in Fairbanks, Interior Alaska, during the ALPACA field campaign in winter 2022, recorded very high concentrations of benzene, toluene, ethylbenzene, and xylene (BTEX), reaching 40–100 ppb during pollution episodes. Lagrangian BTEX tracer simulations capture observed variability but underestimate observations during pollution episodes. Inclusion of previously overlooked oil space heating emissions and accounting for enhanced gasoline vehicle emissions at cold temperatures and at higher relative humidities (warmer temperatures) substantially reduce model biases during polluted periods, except in very stable conditions when results are sensitive to vertical mixing. In the improved model, traffic, then oil, and wood space heating are the main emission sectors contributing to simulated BTEX. Near-surface modeled BTEX are largely confined below surface-based temperature inversions (SBIs) and concentrated over downtown and surrounding residential areas. Intermittent upward transport, even under strongly stable conditions, contributes to regional pollution and potentially to background Arctic haze. Replacing residential wood burning with oil heating during pollution episodes reduces near-surface benzene by up to 20%, highlighting synergies with mitigation strategies designed to reduce particulate matter concentrations. The study findings have implications for an improved understanding of sources of toxic aromatic hydrocarbons in other cold urban winter environments.