Media release
From: AAASAsphalt: A Greater Summertime Source of Harmful Air Pollutants in Large Cities Than Motor Vehicle Gasoline and Diesel Combined
Asphalt emits greater quantities of secondary organic aerosols (small particles with insidious public health effects) under summertime conditions in California’s South Coast Air Basin than gasoline and diesel from motor vehicles combined, according to a new study. The findings point to asphalt as a significant source of air pollution, although one that generally flies under the radar. The industry states that the asphalt manufacturing process removes potential emissions, and emissions from asphalt binder (which holds the material together) are not typically included in inventories. Additionally, Peeyush Khare and colleagues found that asphalt emissions are at their worst during hot, sunny weather, indicating that the material releases more secondary organic aerosols into the air during the summer months. The researchers note that while emissions from motor vehicles are likely to decrease in the years ahead as the most egregious polluters are phased out, asphalt emissions may exert a greater impact as urban areas expand and climate change drives temperatures higher. Previous studies have estimated that a substantial fraction of semi-volatile organic compounds in metropolitan Los Angeles come from a source other than vehicles, yet the culprit has not been identified. To determine how asphalt contributes to urban air pollution, Khare et al. heated commonly used road asphalt to a range of temperatures between 40°Celsius and 200°Celsius (104°Fahrenheit and 392°Fahrenheit) in a temperature-controlled tube furnace. They observed that asphalt emissions doubled when the temperature increased from 40°Celsius to 60°Celsius (104°Fahrenheit to 140°Fahrenheit –temperatures the material typically reaches in the summertime), then climbed by an average of 70% per 20°Celsius (68°Fahrenheit) increase. Although asphalt emissions slowed over the course of one week, they persisted, especially when the material was exposed to sunlight. Khare et al. suggest future studies may employ different methods to more fully capture the extent of the emissions released both during and after asphalt application.
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