AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Light Absorption and Chemical Speciation of Organic Carbon in Wood Smoke, Diesel Exhaust and Urban Particulate Matter
Alena Kubatova, Klara Kukowski, JAMES DIEKMAN, University of North Dakota
Abstract Number: 409 Working Group: Carbonaceous Aerosols in the Atmosphere
Abstract Current climate models either disregard or underestimate the contribution of light absorption by organic carbon (OC) within particulate matter (PM) to radiative forcing. While light absorption by black carbon is recognized, OC was long viewed only as light-scattering. By contrast, recent studies have demonstrated the light absorption potential of OC mainly in the low-visible and ultraviolet wavelengths. To assist developing the climate models, the absorptivities of wood smoke, diesel exhaust and urban PM were measured in the visible and ultraviolet spectrum range using a newly developed instrumentation, vacuum ultraviolet detector coupled to a gas chromatograph (GC-VUV). With GC-VUV, organic compounds were chromatographically separated and their individual absorptions were measured in the gas phase. This setup eliminated the interference of solvent absorption, which is observed in traditional UV-Vis spectrophotometry.
Furthermore, GC-VUV together with GC-MS were used for chemical speciation allowing for a comparison of the OC chemical composition to absorption. To isolate OC from PM, exhaustive Soxhlet extractions were performed using both methanol and dichloromethane. For all three PM samples, OC extraction recoveries were the highest in methanol amounting to 40–60%. However, for wood smoke PM, dichloromethane extracted higher-absorbing compounds compared to methanol. The OC absorptivity was wavelength dependent and decreased towards the visible light region with the highest absorption observed for wood smoke PM. The OC absorptivity at visible light wavelengths correlated with the occurrence of polycyclic aromatic hydrocarbons.