Abstract Number: 289 Working Group: Urban Aerosols
Abstract Abstract. Despite extensive studies into optical properties of fine particle at ground level, comprehensive measurements above the urban canopy has never done before. Simultaneous measurements of physicochemical properties at ground level and 260 m and vertical optical properties in low boundary layer were conducted in urban Beijing during 2016 winter by a series of advanced optical instruments combined with two AMS (a High-Resolution Aerosol Mass Spectrometer and an Aerodyne soot particle-aerosol mass spectrometer) and an Aerosol Chemical Speciation Monitor. Our results showed that the average PM2.5 extinction coefficients are 471.5 Mm-1 and 383.8 Mm-1 at ground level and 260 m, respectively. Compared to the SSA at ground, the SSA at 260 m was slightly higher at night and comparable at day time. Higher values (~1.6) of absorption angstrom exponent were found in this campaign compared to the previously studies, which can be explained as the increase mass fraction of BBOA in PM1. The absorption coefficients at 630 nm of brown carbon were also investigated, which was found to be correlated very well with the mass concentration of BBOA, CCOA and MO-OOA. Similar temporal variations was found between PM1 and PM2.5 scattering coefficients at ground level, the average contribution of PM1 scattering coefficient to PM2.5 scattering coefficient was 62.5% and the average SSA of PM2.5 and PM1 were 0.81 and 0.86, respectively. The OA mass fraction of BC related PM1 was much higher than that of total PM1 (70% vs. 44%), but lensing effect of coating materials on BC was found to be more obvious as the mass fraction of SIA increase, indicating that in addition to the coating thick, the components of coating materials and aged degree may also have impact on the lensing effect. Further studies are needed to investigate the lensing effect and vertical optical properties.
Keyword: Optical properties; Black carbon; Brown carbon; Lensing effect