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Asphalt-related emissions are an understudied source of reactive organic compounds with the potential to form organic aerosol (OA). Ambient aerosol mass spectrometry (AMS) measurements of asphalt-related aerosols near a month-long road paving project showed enhanced ambient OA concentrations with a mix of primary and secondary OA signatures. For comparison, gas-phase emissions from real-world road asphalt samples at application (e.g., 140 °C) and in-use (e.g., 60 °C) temperatures were injected into an environmental chamber and an oxidation flow reactor to simulate varying degrees of oxidative aging while measuring their gas- and aerosol-phase oxidation products. Secondary OA formation was observed via both self-nucleation and condensation, with chemical properties dependent on asphalt temperature and reaction conditions. The chemical composition of less-aged asphalt-related OA observed in outdoor and laboratory measurements was similar to OA from other petrochemical-based sources and hydrocarbon-like OA source factors observed via AMS in previous urban studies. The composition of aged OA varied with the degree of oxidation, similar to oxidized OA factors observed in ambient air. Taken together, these field and laboratory observations suggest that contributions to urban OA during and after application may be challenging to deconvolve from other traditional sources in ambient measurements. 

Abstract. Organic aerosol (OA) emissions from biomass burning havebeen the subject of intense research in recent years, involving acombination of field campaigns and laboratory studies. These efforts haveaimed at improving our limited understanding of the diverse processes andpathways involved in the atmospheric processing and evolution of OAproperties, culminating in their accurate parameterizations in climate andchemical transport models. To bring closure between laboratory and fieldstudies, wildfire plumes in the western United States were sampled andcharacterized for their chemical and optical properties during theground-based segment of the 2019 Fire Influence on Regional to GlobalEnvironments and Air Quality (FIREX-AQ) field campaign. Using acustom-developed multiwavelength integrated photoacoustic-nephelometerspectrometer in conjunction with a suite of instruments, including anoxidation flow reactor equipped to generate hydroxyl (OH⚫) ornitrate (NO3⚫) radicals to mimic daytime or nighttimeoxidative aging processes, we investigated the effects of multipleequivalent hours of OH⚫ or NO3⚫ exposure onthe chemical composition and mass absorption cross-sections (MAC(λ)) at 488 and 561 nm of OA emitted from wildfires in Arizona and Oregon. Wefound that OH⚫ exposure induced a slight initial increase inabsorption corresponding to short timescales; however, at longer timescales, the wavelength-dependent MAC(λ) decreased by a factor of0.72 ± 0.08, consistent with previous laboratory studies and reportsof photobleaching. On the other hand, NO3⚫ exposure increasedMAC(λ) by a factor of up to 1.69 ± 0.38. We also noted somesensitivity of aerosol aging to different fire conditions between Arizonaand Oregon. The MAC(λ) enhancement following NO3⚫ exposure was found to correlate with an enhancement in CHO1N andCHOgt1N ion families measured by an Aerodyne aerosol mass spectrometer.