Primary and Secondary Organic Aerosol Formation from Asphalt Pavements

MACKENZIE HUMES, Jo Machesky, Drew Gentner, Sunhye Kim, Oladayo Oladeji, Neil Donahue, Albert A. Presto, Carnegie Mellon University

     Abstract Number: 389
     Working Group: Aerosol Sources and Constituents of Emerging Importance and Their Impacts across Spatial Scales

Abstract
Asphalt is ubiquitous throughout urban areas worldwide. Asphalt emits gas-phase organic compounds spanning a wide range of volatility, from volatile organic compounds to low-volatility species. The emission rate and composition depend strongly on the temperature and age of the asphalt. For example, Khare et al. showed that emissions are significantly higher at application temperatures (~140°C) than summertime road surface temperatures (~50-70°C), and that the composition of the emissions depends on factors like the presence of UV radiation. Khare et al. also estimated that asphalt paving is a major missing source of intermediate and semivolatile organic compounds in southern California; however, additional studies are necessary to further constrain its contribution to urban particulate matter.

In this study, we evaluate the production of primary and secondary organic aerosols (SOA) from asphalt-related emissions. Fresh and aged roadway asphalt samples were collected from road-paving operations in Pittsburgh and stored in a chemical freezer. Samples were heated fresh and after one month of aging at ambient temperature to either common application temperature (~140°C) or peak summertime road surface temperature (~70°C). The emitted gas-phase vapors were flushed into a smog chamber containing ammonium sulfate seed particles that served as a condensation sink. SOA was then generated via the photo-oxidation of the emissions under high-NOx conditions typical of urban chemistry.

Particle size distributions and composition were determined via scanning mobility particle sizer and an aerosol mass spectrometer respectively. Gas-phase emissions were tracked via Iodide-adduct chemical ionization mass spectrometer and proton transfer reaction mass spectrometer. We compare the aerosol mass spectra of the laboratory-generated asphalt OA to recent ambient data collected adjacent to an asphalt manufacturing plant and at an active road-paving site. Overall, we characterize an understudied but considerable source of organic emissions, demonstrating asphalt’s role in urban SOA and gas-phase oxidation product formation over different timescales.