NOx emissions by real-world fresh and old asphalt mixtures: Impact of temperature, relative humidity, and UV-irradiation

Abstract

Air pollution causes chronic illnesses, and an estimated 4.5 million deaths every year. 70% of mankind is expected to live in cities by 2050, making urban areas key for air quality and related health issues. These areas are largely covered with asphalt pavements. Pollutant emissions from asphalts are generally investigated at 120–160 °C, temperatures that are reached during deposition of asphalt mixtures, but data at in-use temperatures are lacking. In the present work, we characterize and quantify in the laboratory emissions of nitrogen oxides (NOx = NO+NO2) by fresh and old asphalt mixtures under simulated atmospheric conditions. The impact of asphalt aging on NOx emissions is assessed, and the regeneration of NOx emissions by exposure of asphalt to the gas exhaust of a car is evidenced experimentally. With a numerical model of NOx emissions in Athens, Greece, we show that this previously unknown source accounts for up to 20% of NOx emissions in specific locations. Asphalt-covered surfaces can therefore significantly contribute to NOx urban pollution, and need to be included to emission inventories, and taken into account by models for a better understanding and description of factors influencing urban air quality.