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

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 m<sup>2</sup> g<sup>−1</sup> 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 m<sup>2</sup> g<sup>−1</sup> 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<sup>−7</sup>, 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 m<sup>2</sup> g<sup>−1</sup> 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

Carbonaceous and Secondary Inorganic Aerosols during Wintertime Fog and Haze over Urban Sites in the Indo-Gangetic Plain

“…Thus, relatively higher b abs at Allahabad are attributed to the higher EC mass concentrations. The σ abs values, obtained in the present study, are relatively higher compared to those reported over Chinese regions; for example 7.7 m 2 /g (in PM 2.5 samples collected at urban Guangzhou) (Andreae et al, 2008), 9.3 ± 1.4 m 2 /g (for PM 1.0 ) at urban Xinken (Cheng et al, 2008) and 8.45 ± 1.7 m 2 /g for aerosol over Bejing during wintertime (Cheng et al, 2011). There is a lack of scattering coefficient (b scat ) measurements over northern India.…”

Urban impacts on regional carbonaceous aerosols: Case study in central Texas

“…It has also been proposed that atmospheric heating as a result of EC may affect large-scale circulation and the hydrological cycle, leading to significant regional climate effects (Cheng et al, 2011). Typically, EC is treated as the only light-absorbing species in climate models (Kirchstetter et al, 2004;Cheng et al, 2011). However, the effects of light-absorbing organic brown carbon, or BrC, are becoming more apparent and have been reported at 28% of total absorption at lower wavelengths for California (Doherty et al, 2010;Bahadur et al, 2012).…”

“…Among atmospheric pollutants it is second only to CO 2 in potential forcing (Bond et al, 2013). It has also been proposed that atmospheric heating as a result of EC may affect large-scale circulation and the hydrological cycle, leading to significant regional climate effects (Cheng et al, 2011). Typically, EC is treated as the only light-absorbing species in climate models (Kirchstetter et al, 2004;Cheng et al, 2011).…”

Characteristics of Mass Absorption Efficiency of Elemental Carbon in Urban Chengdu, Southwest China: Implication for the Coating Effects on Aerosol Absorption

“…In fact, the MAEs of EC at 632 nm of coal and biomass burning (wheat and rape straws) in this study were 5.6 ± 0.3 and 5.5 ± 0.6 m 2 g −1 , respectively. Moreover, the MAEs of EC at 632 or 650 nm of diesel, biomass burning sources (e.g., crop residual and wood) and coal combustion reported in previous studies ranged from 3.0 to 8.4 m 2 g −1 (Cheng et al 2011;Shen et al 2013). It can be easily seen that the MAEs of EC from source samples were much lower than those obtained in ambient aerosols.…”

“…To compare with other cities, the MAEs of EC at 632 nm were estimated according to AAEs for all seasons in Chengdu. The MAEs of EC were 9.1, 9.7, 9.1 and 9.4 m 2 g −1 , respectively, in spring, summer, autumn and winter, which were slightly higher than those measured in summer (9.4 m 2 g −1 ) and winter (7.5-8.5 m 2 g −1 ) in Beijing (Cheng et al 2011;Wu et al 2016). In fact, the MAEs of EC at 632 nm of coal and biomass burning (wheat and rape straws) in this study were 5.6 ± 0.3 and 5.5 ± 0.6 m 2 g −1 , respectively.…”