Black Carbon Aging from SOA Coatings and Coagulation with Diesel BC Emissions during SAAS at the PNNL Environmental Chamber

Allison C Aiken1, Shang Liu2,3, Manvendra Krishna Dubey4, Rahul A Zaveri5, John E Shilling6, Gourihar Kulkarni7, Mikhail S Pekour6, R Subramanian8, Alla Zelenyuk6, Jacqueline Mary Wilson9, Claudio Mazzoleni10, Swarup China11 and Noopur Sharma12, (1)Los Alamos National Laboratory, Earth and Environmental Science Division, Los Alamos, NM, United States, (2)Los Alamos National Laboratory, Los Alamos, NM, United States, (3)University of Colorado at Boulder, Boulder, CO, United States, (4)Los Alamos National Laboratory, Earth and Environmental Science Division, Los Alamos, United States, (5)Pacific Northwest Natl Lab, Richland, United States, (6)Pacific Northwest National Laboratory, Richland, WA, United States, (7)Pacific Northwest National Laboratory, Richland, United States, (8)Carnegie Mellon University, Department of Mechanical Engineering, Pittsburgh, PA, United States, (9)Battelle Pacific Northwest, Richland, United States, (10)Michigan Technological University, Physics, Houghton, MI, United States, (11)Michigan Technological University, Houghton, MI, United States, (12)Michigan Technological Univ, Houghton, MI, United States
Abstract:
Black carbon (BC) is considered to be potentially the 2nd most important global warming factor behind CO2 (Bond et al., 2013). Uncertainties exist due to BC morphology and mixing state on the extent of the warming that it causes, e.g. Cappa et al., 2012. Core-shell BC is expected to enhance absorption by up to a factor of 2, but has yet to be observed to this extent from ambient data. Experiments were conducted during the Soot Aerosol Aging Study (SAAS) Laboratory Campaign at Pactific Northwest National Laboratory’s Environmental Chamber in the winter of 2013-2014 to investigate the relationship between coatings and enhancements from diesel emissions.

Direct on-line measurements were made with the single particle soot photometer (SP2) from fresh and aged BC from coating and coagulation experiments with secondary organic aerosol (SOA) formed in the chamber. BC measurements are coupled with photoactoustic measurements spanning the visible region to probe BC enhancements when mixed with SOA. Here we focus on the enhancements at 781 nm, that are tracked throughout SOA growth on BC, as determined from SP2 coating thicknesses. Thermal denuder (TD) experiments are conducted and enhancements are calculated from two different methods that agree well with each other, confirming the observed results. BC measurements are also compared with co-located measurements from SPLAT-II and filter analysis using SEM and TEM.

BC coagulated with SOA produces minimal absorption enhancement values, whereas coatings are observed to have significant enhancement values at 300 degrees C, e.g. 1.3 for thickly coated BC. BC particles were coagulated with SOA in the chamber since this morphology has been observed in wildfire emissions (Sedlacek et al., 2012). Since we did not observe appreciable enhancements for the coagulated BC, we expect that ambient emissions dominated by this particle type to have enhancements due to other sources, such as brown carbon (BrC) that is often co-emitted (Saleh et al., 2014).

We also observed thickly coated BC that is not detected by the SP2 when the coatings are too thick for the laser to evaporate the coating and for the BC core to receive enough energy from the laser to incandesce. This noted caveat warrants more research to determine how prevalent this BC particle type is and how it would be expected to impact climate.

Back to: Multimodal Characterization of Atmospheric Aerosols Using Unique Capabilities of DOE User Facilities II Posters