Primary and Secondary Organic Aerosol Formation from Asphalt Pavements

Asphalt is ubiquitous across cities and a source of organic compounds spanning a wide range of volatility and may be an overlooked source of urban organic aerosols. The emission rate and composition depend strongly on temperature, but emissions have been observed at both application temperatures and surface temperatures during warm sunny days. Here we report primary organic aerosol (POA) emissions and secondary organic aerosol (SOA) production from asphalt. We reheated real-world asphalt samples to application-relevant temperatures (similar to 130(degrees)C) and typical summertime road-surface temperatures (similar to 55 C-degrees) and then flushed the emitted vapors into an environmental oxidation chamber containing ammonium sulfate seed particles. SOA was then formed following the photo-oxidation of emissions under high-NO x conditions typical of urban atmospheres. We find that POA only forms at application temperature as it does not require further oxidation, whereas SOA forms under both conditions; with the resulting POA and SOA both being semi-volatile. While total OA formation rates were substantially greater under the limited time spent under application conditions, SOA formation from passive asphalt heating presents a potential long-term source, as heating continues for the lifetime of the road surface. This suggests that persistent asphalt solar heating is likely a considerable and continued source of summertime SOA in urban environments.

Automated summary

Asphalt, commonly found in cities, can emit primary and secondary organic aerosols. The emission rate and composition depend on temperature, and emissions have been observed at both application temperatures and warm surface temperatures. Primary organic aerosols only form at application temperature, while secondary organic aerosols form under both conditions. Both types of aerosols are semi-volatile. Passive asphalt heating can also lead to the formation of secondary organic aerosols, making it a potential long-term source of summertime aerosols in urban environments.