Mass absorption efficiency of elemental carbon and water-soluble organic carbon in Beijing, China

Y Cheng,M Zheng,R J Weber,Y.-L Ma,F.-K Duan,F.-M Yang,K.-B He,A G Russell,Z.-Y Du,J.-M Liu,X.-L Zhang,J.-H Tan,M H Bergin

doi:10.5194/acp-11-11497-2011

Abstract

Abstract. The mass absorption efficiency (MAE) of elemental carbon (EC) in Beijing was quantified using a thermal-optical carbon analyzer. The MAE measured at 632 nm was 8.45±1.71 and 9.41±1.92 m2 g−1 during winter and summer respectively. The daily variation of MAE was found to coincide with the abundance of organic carbon (OC), especially the OC to EC ratio, perhaps due to the enhancement by coating with organic aerosol (especially secondary organic aerosol, SOA) or the artifacts resulting from the redistribution of liquid-like organic particles during the filter-based absorption measurements. Using a converting approach that accounts for the discrepancy caused by measurements methods of both light absorption and EC concentration, previously published MAE values were converted to the equivalent-MAE, which is the estimated value if using the same measurement methods as used in this study. The equivalent-MAE was found to be much lower in the regions heavily impacted by biomass burning (e.g., below 2.7 m2 g−1 for two Indian cities). Results from source samples (including diesel exhaust samples and biomass smoke samples) also demonstrated that emissions from biomass burning would decrease the MAE of EC. Moreover, optical properties of water-soluble organic carbon (WSOC) in Beijing were presented. Light absorption by WSOC exhibited strong wavelength (λ) dependence such that absorption varied approximately as λ−7, which was characteristic of the brown carbon spectra. The MAE of WSOC (measured at 365 nm) was 1.79±0.24 and 0.71±0.20 m2 g−1 during winter and summer respectively. The large discrepancy between the MAE of WSOC during winter and summer was attributed to the difference in the precursors of SOA such that anthropogenic volatile organic compounds (AVOCs) should be more important as the precursors of SOA in winter. The MAE of WSOC in Beijing was much higher than results from the southeastern United States which were obtained using the same method as used in this study, perhaps due to the stronger emissions of biomass burning in China.

Highlights

Carbonaceous aerosol has been the focus of extensive studies during the last decade due to its complex effects on human health, visibility and climate change
DependeFcneicnge.tr6ao.tifDobneapdbesunrmdineegnacwseuiorneftedbraaabtns d3m6seu5amnsummreedor.naLtt3ihn6ee5aWnr mrSegoOrneCsthscieooWnnrcSeeOsnuCtlrtsactoainroe-n duripnegrfworimnteedr aantd632 nm and the elemental carbon (EC) concentration mined by the IMPROVE-A temperature protocol was with detertransshown with K as the slope
Effects of biomass burning on the mass absorption efficiency (MAE) of water-soluble organic carbon (WSOC) could be illustrated by results from the southeastern United States

Summary

Introduction

Carbonaceous aerosol has been the focus of extensive studies during the last decade due to its complex effects on human health, visibility and climate change. Y. Cheng et al.: MAE of EC and WSOC organic carbon (OC) and elemental carbon (EC) by thermaloptical (or thermal) method (Chow et al, 1993; Birch and Cary, 1996). Cheng et al.: MAE of EC and WSOC organic carbon (OC) and elemental carbon (EC) by thermaloptical (or thermal) method (Chow et al, 1993; Birch and Cary, 1996) Another widely used definition is black carbon (BC), which is the light-absorbing carbon measured by optical instruments such as Aethalometer (Hansen and Novakov, 1990). In the emission-inventory and climate-science community, black carbon is usually used synonymously with EC, because the emission factors of BC are typically measured by thermal-optical (or thermal) methods (e.g., Chen et al, 2009). Atmospheric heating caused by black carbon may affect the large scale circulation and the hydrological cycle with significant regional climate effects that contribute to the observed precipitation and temperature changes in China (Ramanathan et al, 2001; Menon et al, 2002)

Methods

Results

Conclusion