AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Black and Brown Carbon at Duke Forest, A Biogenic Environment Impacted by Urban Influence
R. SUBRAMANIAN, Antonios Tasoglou, Spyros Pandis, Andrey Khlystov, Carnegie Mellon University
Abstract Number: 343 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract Black carbon (BC) is a significant climate warming agent, while light-absorbing organic carbon, called brown carbon (BrC), also impacts the atmospheric radiative balance. There is strong evidence that the optical properties of ambient aerosols, especially BC, are affected by biogenic secondary organic aerosol (SOA) through the lensing effect (coating of BC cores by semivolatile SOA), in addition to the potential formation of BrC from biogenic emissions influenced by anthropogenic sources. To evaluate these effects, measurements of ambient aerosol optical properties and chemical composition were made at Duke Forest (Chapel Hill, NC) during summer 2015, using photoacoustic extinctiometers (DMT PAX, 405 nm and 532 nm), a seven-wavelength Aethalometer, a steam-jet aerosol collector (SJAC), and a single particle soot photometer (SP2). For absorption and BC measurements, the sample was cycled between a dry line and a dry/thermally-denuded line. We found strong evidence for non-BC light absorption at Duke Forest that appears linked to a low-volatility aerosol component. For example, the Aethalometer readings at Duke Forest showed greater near-UV and blue absorption compared to absorption at 880 nm, than can be accounted for by an inverse wavelength dependence, as would be the case if BC was the only absorbing agent. On some afternoons, the blue PAX also recorded significant aerosol light absorption, which was not associated with BC. We also saw a diurnal pattern in the BC light absorption enhancement (E$_(abs)), which was greater at night than during the day. Hourly samples collected with the SJAC are being analyzed offline for aerosol chemical composition, to gain insight into the relationship of non-BC light absorption to aerosol chemistry and sources.