Abstract
Abstract. Brown carbon (BrC) draws increasing attention due to its effects on climate and other environmental factors. In China, household coal burned for heating and cooking purposes releases huge amounts of carbonaceous particles every year; however, BrC emissions have rarely been estimated in a persuasive manner due to the unavailable emission characteristics. Here, seven coals jointly covering geological maturity from low to high were burned in four typical stoves as both chunk and briquette styles. The optical integrating sphere (IS) method was applied to measure the emission factors (EFs) of BrC and black carbon (BC) via an iterative process using the different spectral dependence of light absorption for BrC and BC and using humic acid sodium salt (HASS) and carbon black (CarB) as reference materials. The following results have been found: (i) the average EFs of BrC for anthracite coal chunks and briquettes are 1.08 ± 0.80 and 1.52 ± 0.16 g kg−1, respectively, and those for bituminous coal chunks and briquettes are 8.59 ± 2.70 and 4.01 ± 2.19 g kg−1, respectively, reflecting a more significant decline in BrC EFs for bituminous coals than for anthracites due to briquetting. (ii) The BrC EF peaks at the middle of coal's geological maturity, displaying a bell-shaped curve between EF and volatile matter (Vdaf). (iii) The calculated BrC emissions from China's residential coal burning amounted to 592 Gg (1 Gg = 109 g) in 2013, which is nearly half of China's total BC emissions. (iv) The absorption Ångström exponents (AAEs) of all coal briquettes are higher than those of coal chunks, indicating that the measure of coal briquetting increases the BrC ∕ BC emission ratio and thus offsets some of the climate cooling effect of briquetting. (v) In the scenario of current household coal burning in China, solar light absorption by BrC (350–850 nm in this study) accounts for more than a quarter (0.265) of the total absorption. This implies the significance of BrC to climate modeling.
Highlights
The past decade saw increased interest in brown carbon (BrC) due to its effects on atmospheric chemistry, air quality, health, and climate (Andreae and Gelencsér, 2006; Saleh et al, 2014; Forrister et al, 2015; Laskin et al, 2015)
The general motivation of this study is to investigate the emissions and optical characteristics of Brown carbon (BrC) emitted by China’s household coal burning
Since the briquettes of the seven coals were only burned in the Wanjia brand briquette stove (WJ) stove and the chunks of all seven coals were burned in the three chunk stoves (SC, Huanding brand chunk stove (HD), Laowan brand chunk stove (LW)) one by one, there was a total of 28 coal and stove combinations for the emission test
Summary
The past decade saw increased interest in brown carbon (BrC) due to its effects on atmospheric chemistry, air quality, health, and climate (Andreae and Gelencsér, 2006; Saleh et al, 2014; Forrister et al, 2015; Laskin et al, 2015). The former relates to the incomplete (even smoldering) combustion of either fossil fuels (coal, petroleum, natural gas, etc.) or biomass– biofuels (wood, agricultural residues, bioethanol, etc.), during which BrC is generated and released into the atmosphere as pollutants (Liu et al, 2014; Oris et al, 2014; Washenfelder et al, 2015; Zhi et al, 2015) The latter involves complex chemical reactions taking place in the atmosphere between various precursors, forming secondary organic aerosols (SOAs), some of which are light-absorbing (Laskin et al, 2014; Lee et al, 2014; Smith et al, 2014; Tóth et al, 2014; Martinsson et al, 2015; Yan et al, 2015; Zhao et al, 2015). The calculated BrC emissions and lightabsorbing contributions add to the importance of China’s household coal burning in both climate and air quality
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