Humidity: A hidden driver of toxic emissions and asphalt decay in a changing climate

Amid climate change and extreme weather, non-tailpipe air pollution from asphalt surfaces significantly contributes to urban air pollution. This study integrates laboratory experiments, field data, and computational modeling to show that humidity is a key driving factor that increases polar VOC emissions from asphalt by up to 46% when relative humidity rises from near-dry conditions (RH < 0.1%) to humid conditions (50% RH) at 50 °C. These VOCs also form SOAs, posing health and environmental risks. FTIR, MD simulations, and DFT calculations reveal that humid conditions enhance VOC-water interactions at the asphalt surface, increasing the abundance of oxygenated functional groups and hydrophilicity. This, combined with solar radiation, accelerates surface degradation through a self-reinforcing cycle. Analyzing a dataset of over 5000 observations from 1400 U.S. road segments spanning more than three decades, we develop a panel model that highlights the interaction between humidity range and solar exposure in accelerating asphalt deterioration. The nonlinear humidity term is statistically significant (p = 0.024), and the humidity-sunshine interaction is strongly positive (p < 0.001). Results highlight humidity's critical role in both degradation and emissions, emphasizing the need to explicitly consider humidity and its interaction with solar radiation in climate-resilient pavement design and air quality management strategies. TEASER: The Hidden Role of Humidity in Increasing Toxic VOC Emissions and Accelerating Asphalt Pavement Deterioration.