Abstract
Abstract. Recent studies have highlighted the importance of brown carbon (BrC) in various fields, particularly relating to climate change. The incomplete combustion of biomass in open and contained burning conditions is believed to be a significant contributor to primary BrC emissions. So far, few studies have reported the emission factors of BrC from biomass burning, and few studies have specifically addressed which form of light-absorbing carbon, such as black carbon (BC) or BrC, plays a leading role in the total solar light absorption by biomass burning. In this study, the optical integrating sphere (IS) approach was used, with carbon black and humic acid sodium salt as reference materials for BC and BrC, respectively, to distinguish BrC from BC on filter samples. A total of 11 widely used biomass types in China were burned in a typical stove to simulate the real household combustion process. (i) Large differences existed in the emission factors of BrC (EFBrC) among the tested biomass fuels, with a geometric mean EFBrC of 0.71 g kg−1 (0.24–2.09). Both the plant type (herbaceous or ligneous) and burning style (raw or briquetted biomass) might influence the value of EFBrC. The observed reduction in the emissions of light-absorbing carbon (LAC) confirmed an additional benefit of biomass briquetting in climate change mitigation. (ii) The calculated annual BrC emissions from China's household biomass burning amounted to 712 Gg, higher than the contribution from China's household coal combustion (592 Gg). (iii) The average absorption Ångström exponent (AAE) was (2.46±0.53), much higher than that of coal-chunk combustion smoke (AAE=1.30±0.32). (iv) For biomass smoke, the contribution of absorption by BrC to the total absorption by BC+BrC across the strongest solar spectral range of 350–850 nm (FBrC) was 50.8 %. This is nearly twice that for BrC in smoke from household coal combustion (26.5 %). (v) Based on this study, a novel algorithm was developed for estimating the FBrC for perhaps any combustion source (FBrC=0.5519lnAAE+0.0067, R2=0.999); the FBrC value for all global biomass burning (open+contained) (FBrC-entire) was 64.5 % (58.5 %–69.9 %). This corroborates the dominant role of BrC in total biomass burning absorption. Therefore, the inclusion of BrC is not optional but indispensable when considering the climate energy budget, particularly for biomass burning emissions (contained and open).
Highlights
Brown carbon (BrC) refers to the fraction of organic carbon (OC) that is light-absorbing, with a pronounced wavelength dependence of absorption (Kirchstetter et al, 2004; Bosch et al, 2014; Chakrabarty et al, 2014; Mo et al, 2017; Jiang et al, 2018; Sun et al, 2018)
Few studies have reported the emission factors of brown carbon (BrC) from biomass burning, and few studies have addressed which form of light-absorbing carbon, such as black carbon (BC) or BrC, plays a leading role in the total solar light absorption by biomass burning
carbon black (CarB) and humic acid sodium salt (HASS) were used as proxies for BC and BrC, respectively, to characterize household coal burning samples by assuming that BC and BrC in household coal emissions had the same light-absorbing properties as CarB and HASS, respectively (Sun et al, 2017). We extended this logic and assumed that BC and BrC in household biomass smoke have the same light-absorbing properties as CarB and HASS, respectively
Summary
Brown carbon (BrC) refers to the fraction of organic carbon (OC) that is light-absorbing, with a pronounced wavelength dependence of absorption (Kirchstetter et al, 2004; Bosch et al, 2014; Chakrabarty et al, 2014; Mo et al, 2017; Jiang et al, 2018; Sun et al, 2018). Unlike other regions where firewood often plays a major role as a biomass fuel, China has more access to agricultural waste (e.g., maize straw, wheat straw, and rice straw) for household heating and cooking purposes (Huang et al, 2012; Shen et al, 2013; Chen et al, 2015a) This suggests that studies of BrC originating from China’s household biomass fuel combustion should consider as many biomass fuel varieties as possible so that the actual characteristics of BrC emissions can be comprehensively investigated and represented. The integrating sphere (IS) method, which was refined in a previous study of residential coal combustion (Sun et al, 2017), was used here to simultaneously quantify BrC and BC Based on this intensive study of contained biomass burning (in stoves), we extrapolated the results to develop a novel algorithm for estimating the contribution of solar light absorption by BrC to the sum of BC + BrC for perhaps any combustion source. This will help to gain a clearer idea of whether BC or BrC dominates the light absorption properties of biomass burning (contained plus open) on a global scale
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
