VOC emissions by fresh and old asphalt pavements at service temperatures: impacts on urban air quality

Abstract

Outdoor air pollution is a major cause of chronic illness and of mortality, with an estimated 4.5 million deaths every year. Its effects are amplified in urban areas where the global population concentrates at an increasing pace. Asphalt-covered surfaces dominate urban areas. Although pollutant emissions from asphalt have been investigated at temperatures above 120 °C during laying, data on emissions at service temperatures are lacking. In the present work, we characterize and quantify in the laboratory volatile organic compound (VOC) emissions by fresh and old asphalt mixtures with gas chromatography – mass spectrometry/flame ionization detector (GC-MS/FID) and proton transfer reaction – time of flight mass spectrometry (PTR-ToFMS) under simulated atmospheric conditions at service temperatures (23–60 °C). The impact of asphalt aging on VOC emissions is assessed. We show that asphalt pavements contribute significantly to urban pollution and therefore need to be included to emission inventories and taken into account by air quality models. VOC emissions from these extended surfaces are shown to be important contributors to ozone and secondary organic aerosol formed in urban areas. This study reveals a large background source of VOCs, precursors of ozone and particulate matter in cities. Specifically, we estimate that in Paris (France), asphalt pavements at service temperatures are responsible for the emission of 0.148 Gg NMVOC per year, corresponding to 21.3% of emissions from road transportation, and 2.9% of total NMVOC emissions in 2019. The corresponding mass of formed Secondary Organic Aerosol (SOA) is estimated as 1.60–4.12 tonnes per year, accounting for 1.5–3.8% of PM₁ emitted by road transportation. It suggests that “net zero emissions” targets, such as the zero pollution action plan of the European Green Deal, cannot be met until this new challenge from asphalt pavements is acknowledged and tackled. Reducing emissions from asphalt pavements during service is a major challenge for sustainable cities and needs to be addressed by the scientific community, policy makers and industrial partners.