AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Size-resolved Measurements of Water and Methanol-extracted Brown Carbon in Beijing
ZHENYU DU, Yuan Cheng, Jiumeng Liu, Shuping Dong, Ting Zhang, Yuwu Li, CNEAC, China
Abstract Number: 542 Working Group: Urban Aerosols
Abstract Contribution of light-absorbing organics, namely brown carbon, to total light absorption budget of atmospheric particles was of crucial importance for estimating the climatic effect of atmospheric particles. However, direct measurement of light absorption of brown carbon was still elusive. In this case size-resolved atmospheric particulate matter was collected in Beijing during April of 2016 using a cascade impactor. Solution light absorption spectra of both water and methanol-extracted brown carbon were measured with a UV-Vis spectrophotometer equipped with Liquid Waveguide Capillary Cell, and water-soluble organic carbon (WSOC), organic and elemental carbon (OC and EC) were analyzed. Meanwhile, light absorption of atmospheric fine particle was observed with a multi-angle absorption photometer (MAAP). Size distribution of absorption of water and methanol extracts both exhibited significant temporal variations. In days with severe air pollution, the absorption of water and methanol extracts mostly peaked between 0.18-0.56 μm (aerodynamic mean diameter), while in days with fine air quality the light absorption also peaked around an aerodynamic mean diameter of 1.8 or 2.5 μm. However, the mass absorption efficiency of water and methanol extracts were highest with aerodynamic mean diameter between 0.18-0.56 μm. Absorption refractive indices were calculated for water and methanol extracts of particles with aerodynamic mean diameter below 2.5 μm based on their solution light-absorption properties, and Mie theory was applied to estimate the light absorption of atmospheric particles comprised of water and methanol-extracted brown carbon, assuming brown carbon and other components of particles were externally mixed. It was found that the contribution of brown carbon absorption predicted by Mie theory to total fine particle light absorption slightly dropped when the absolute absorption of brown carbon increased during April of 2016 in Beijing. Generally, the absorption of brown carbon contributed about 30% to total fine particle absorption at the wavelength of 365 nm, similar with the result of another research in Atlanta and Yorkville, indicating an important role of brown carbon played on radiative forcing.