中国秸杆焚烧及民用燃煤棕色碳排放的初步研究

近年来的研究表明,在BC(黑碳)和OC(有机碳)之间,还存在着一种有弱吸光能力的OC,因大多显棕黄色而被称为BrC(brown carbon,棕色碳). 广泛存在的秸杆焚烧和冬季大量民用燃煤的使用,使国内BrC排放严重,但鲜见对其排放量的测算. 采用七波段黑碳仪(aethalometer)方法,对夏季小麦秸杆焚烧过程及冬季民用炉燃煤过程产生的烟气进行现场监测,根据BrC与BC的光谱关联性差别,分化出R_BrC/BC(总光学衰减中BrC和BC的相对贡献). 结果表明:麦秆焚烧和民用燃煤烟气的R_BrC/BC分别为1.754±0.278和0.183±0.142. 借助R_BrC/BC值,结合现有的BC排放清单(2000年),初步推算出中国民用燃煤和秸杆田间焚烧BrC的排放总量(以BC当量计,下同)为(270.6±101.6)Gg,接近同期BC排放量的一半；其中秸杆焚烧的BrC排放量为(175.4±27.8)Gg,约占二者总量的65%；民用燃煤的BrC排放量为(95.2±73.7)Gg,约占35%. 该研究结果可为更全面的BrC排放测算奠定基础,并为研究BrC的大气化学及辐射强迫提供依据. 

A Preliminary Study on Brown Carbon Emissions from Open Agricultural Biomass Burning and Residential Coal Combustion in China

Recent studies suggest that, between ordinary organic carbon (OC, non-light-absorbing) and black carbon (BC, strongly light-absorbing) in atmospheric carbonaceous aerosols, there are some light-absorbing organic carbon aerosols collectively termed brown carbon (BrC). Although China has large BrC emissions from residential coal combustion and open agricultural biomass burning, there are little specific BrC emissions or testing data available. A 7-wavelength aethalometer was used to monitor the light-absorbing features of primary aerosols emissions from summertime open burning of wheat straw and from wintertime combustion of residential coal. Based on distinctions in the spectral dependence between BrC and BC (the ngstrm index is theoretically 1.0for BC and is greater than 1.0for BrC), the relative Shares of BrC and BC (B_BrC/BC ratio) were calculated. The results show that the value was 1.754±0.278for wheat straw and 0.183±0.142for residential coal. Based on the BrC/BC ratios obtained,preliminary estimates of China's BrC emissions from residential coal and open agricultural biomass burning in 2000were calculated with the help of corresponding BC emissions reported in previous studies. The yearly sum of BrC emissions from residential coal and open agricultural biomass burning was 270.6±101.6Gg (BC equivalent) in China, with (175.4±27.8) Gg or approximately 65% attributable to field agricultural biomass and (95.2±73.7) Gg or approximately 35%, to residential coal. These findings would establish a foundation for a more comprehensive measurement of BrC emissions in the future as well as studies of BrC in atmospheric chemistry and radiation forcing.