Hot asphalt releases aerosols that form secondary particulate matter in the air. In warm regions, more particulate matter is generated than by the entire road traffic. Fine dust leads to damage to heart cells and lung diseases, promotes heart attacks, and can even cause cancer. In Europe, the air’s particulate matter load is highest in autumn and winter because, in addition to cars and trucks, open fires and oil heaters emit tiny particles into the atmosphere during these seasons. A study by Yale University has now identified one of the main sources of secondary particulate matter that causes most of the air pollution in summer. According to the research published in the journal Science Advances, aerosols form from asphalt at high temperatures, rise into the air, and combine with other gases to form particulate matter. Asphalt itself does not produce particulate matter in the process, but it releases the necessary chemicals into the air, from which secondary particulate matter is formed.
The analysis of the pavement under laboratory conditions shows that the release of precursor gases increases at 40 degrees Celsius soil temperature. At 60 degrees Celsius soil temperature, the release doubles. This is a temperature that is frequently reached in Germany because, on average, the soil temperature is twice as high as the air temperature. On the southern coast of California, which served as a study region for the scientists, more particulate matter is generated by asphalt due to the many hot days than by all combustion engines of cars or motorcycles on the road. Additionally, the scientists analyzed the aerosols using mass spectrometry. They observed that sunlight increases emissions by 300 percent. For asphalt mixtures with sulfur content, emissions increased by 700 percent due to sunlight, and for oxygen-containing asphalt mixtures, emissions increased by 400 percent. Therefore, the study authors conclude that in addition to high temperatures, sunlight also increases particulate matter pollution in cities. This is particularly problematic because, according to environmental chemists, there are currently no alternatives to asphalt.
In conclusion, the study by Yale University has identified hot asphalt as one of the main sources of secondary particulate matter that causes most of the air pollution in summer. The release of precursor gases from asphalt increases with soil temperature, and sunlight further increases emissions. This is a significant problem because there are currently no alternatives to asphalt. The findings of this study highlight the urgent need for measures to reduce particulate matter pollution in cities, especially during the summer months.
