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什么是黑碳?概述、影响和缓解策略

已有 1327 次阅读 2022-9-25 14:59 |系统分类:科研笔记

什么是黑碳?概述、影响和缓解策略

--我们可以做些什么来解决全球变暖的第二大原因。


来源于: https://www.treehugger.com/what-is-black-carbon-5201028

作者:David M. Kuchta         出版时间:2021/10/26                翻译:刘敏

 

黑碳(Black Carbon, BC)作为烟尘和烟雾的主要成分之一,是木柴或化石燃料等含碳物质不完全燃烧的产物。在恰当的地方,黑碳是土壤重要的天然肥料,这也是人们几千年来实行刀耕火种的原因。在不恰当的地方,当黑碳沉积在肺部深处,可导致过早死亡,当黑碳沉积在雪地上,可增加灾难性洪水的风险。悬浮在大气中的黑碳是继二氧化碳(CO2)之后导致全球变暖的第二大因素。由于黑碳对弱势群体的过度影响,解决黑碳问题是一个环境正义问题。

一、黑碳来源

工业革命之前,自然或人为活动引起的火灾是黑碳的主要来源。作为自然碳循环的一部分,生物质燃烧产生的固态黑碳(生物炭)多于空气中的黑碳(烟尘)[1]。火灾更多的将碳封存在土壤中而不是排入大气中,排入大气中的碳可被植物重新吸收[2]

土壤中高达40%的有机碳是黑碳[3],主要作用是增加土壤的肥力。即使现在,人们也常使用生物炭来提高因密集型工业农业而退化土壤的肥力[4]

自十八世纪末工业化开始以来,煤炭(最脏的化石燃料[5])取代生物燃料成为黑碳排放的主要来源[6]。大气中的黑碳(烟尘)增加了七倍,并在二十世纪初达到顶峰。

1664089077011.png

1952年的伦敦大烟雾主要是黑碳. Fox Photos/Hulton Archive/Getty Images

然而,生物质的燃烧仍在继续,特别是在低收入国家的农村地区。全世界有20亿人使用生物质(木材、粪便或作物残渣)作为取暖和烹饪的主要燃料[8]。事实上,随着20世纪人口的快速增长[9],生物质的燃烧增加了一倍,低效的炉灶是一个主要来源[10]

全球范围内化石燃料的碳排放大约是生物质源的两倍,约占所有黑碳排放的25%[11]。不同源对大气黑碳的贡献依地区的工业化和城市化而有所不同,生物质在农村地区贡献更多的黑碳,而化石燃料在城市地区贡献更多[12]

继化石燃料和生物质之后,来自汽车尾气、刹车和轮胎磨损的路尘是黑碳的第三排放源。现今,柴油机尾气排放了交通部门90%的黑碳[13],高于任何其他单一来源。作为城市颗粒物(PM2.5)的重要组成部分,道路附近的黑碳水平可能高出50%至200%[14]。在燃煤电厂周围,沉积在道路上或附近的烟尘会重新悬浮在空气中。

二、黑碳的危害

黑碳的影响既是一个地方性问题,也是一个全球性问题,其影响取决于排放源以及排放地点。生物质源的黑碳对人类健康有局部影响,而化石燃料所产生的黑碳会造成更大的全球性问题,如增加自然灾害和全球变暖的风险。

1.      对人体健康的影响

虽然黑碳在大气中停留时间较短(几天-十几天),但它对人类健康的影响巨大[16]。根据两项研究,在农村地区,来自炉灶的家庭黑碳空气污染对妇女和幼儿的影响不成比例[17]。在城市地区,道路灰尘,特别是靠近煤厂和港口设施的灰尘,也有类似的风险,低收入家庭和有色人种接触黑碳的机会明显增加[18]。例如,在底特律地区的一项研究中,弱势和有色人种社区的近道路黑碳浓度比其他地方高35%-40%[19]

黑碳已被确定为温室气体排放的 "第二大 "来源[20]。来自化石燃料燃烧的黑碳全球变暖潜力是生物质源的两倍[21]。由于黑碳吸收而不是反射辐射,它阻挡了通常会逃逸太空的能量离开地球大气层,从而促进了全球变暖。

无论黑碳是降落地面还是悬浮在大气中,情况都是如此。当黑碳降落于雪地,其影响巨大,变黑的雪不再将光线反射至太空,而是吸收更多的热能。根据最近的研究,黑碳可解释冰川和融雪加速50%以上的原因。在极地地区,这是海平面上升的一个直接原因[22]

2.      自然灾害

在冰川等常年结冰的区域,黑碳的存在增加了洪水风险。喜马拉雅山脉的冰川融化增加了生活在恒河和雅鲁藏布江流域的7800万人的洪水风险[23]。黑碳与中国北方干旱和中国南方洪水的频率增加有关,也与源自阿拉伯海的热带气旋的强度增加有关[24]

三、技术解决方案

黑碳主要影响的是生活在贫困中、发展中国家和世界各地的有色人群,因此黑碳是一个环境正义问题。需要指出的是,目前已存在缓解黑碳排放的方法。实施这些措施可以改善人类健康,并在2050年前可将全球变暖降低0.2摄氏度[25]黑碳和CO2通常在相同燃烧过程中排放(如柴油燃烧),因此许多减少CO2排放的努力也会产生减少黑碳的效果。然而,一些缓解的技术方案对于减少黑碳排放水平特别重要。

更清洁的燃烧炉灶。如太阳能灶有可能减少农村黑碳排放,减缓森林砍伐,改善人类健康,并提高教育水平。因为儿童如将大量时间收集木柴,将削减他们的教育机会[26]

1664089113968.png

赞比亚的太阳能炊具。Tina Stallard/Getty Images

再生农业。包括将碳和其他营养物质返回到土壤中以维持土壤健康。黑碳在土壤中持续稳定了几千年[27],将其作为生物炭返回土壤也可以作为一种碳耕作或 "负排放 "的形式[28]

混合动力汽车和电动汽车。主要依靠再生制动而不是摩擦制动来降低道路灰尘水平,而摩擦制动产生的颗粒物约占道路交通产生颗粒物的20%[29]

更少和更清洁的交通可减少黑碳暴露。低排放区(LEZs)也是有效的,伦敦的低排放区减少了40%-50%的黑碳。 减少卡车的柴油污染也可以改善低收入和弱势社区的健康状况[30]。加州长滩港这样一个项目赢得了美国环保局的环境正义成就奖。

更清洁的航运。由于黑碳只在大气中停留几天,减少船舶在极地等敏感地区的黑碳排放,对减少融雪和海平面上升有很大影响[31]

 

参考文献:

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22.    Mani, Muthukumara. Glaciers of the Himalayas: Climate Change, Black Carbon, and Regional Resilience. Washington, D.C.: World Bank Publications, 2020, 2, 113.

23.    ibid.

24.    Fan, Jiwen, et al. “Substantial contribution of anthropogenic air pollution to catastrophic floods in Southwest China.” Geophysical Research Letters 42 (20 July 2015), 6066-6075. doi:10.1002/2015GL064479; Menon, Surabi, James Hansen, Larissa Nazarenko, and Yunfeng Luo. “Climate Effects of Black Carbon Aerosols in China and India.” Science 297:5590 (27 September 2002), 2250-2253. DOI: 10.1126/science.1075159.; Evan, Amato T, et al. “Arabian Sea tropical cyclones intensified by emissions of black carbon and other aerosols.” Nature 479:7371 (November 3, 2011), 94-97. DOI:10.1038/nature10552.

25.    Sims, R., V. Gorsevski and S. Anenberg. Black Carbon Mitigation and the Role of the Global Environment Facility: A STAP Advisory Document. United Nations Global Environment Facility, Washington, D.C., 2015.

26.    Levison, Deborah, Deborate S. DeGraff and Esther W. Dungumaro. “Implications of Environmental Chores for Schooling: Children’s Time Fetching Water and Firewood in Tanzania.” The European Journal of Development Research 30:2 (April 2018), 217-234. DOI:10.1057/s41287-017-0079-2.

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28.    Smith, Pete. “Soil carbon sequestration and biochar as negative emission technologies.” Global Change Biology 22:3 (March 2016), 1315-1324. https://doi-org.une.idm.oclc.org/10.1111/gcb.13178.

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30.    Urban Access Regulations in Europe. “Impact of Low Emission Zones.”

31.    Kong, Qingxu, Changmin Jiang, and Adolph K.Y. Ng. “The economic impacts of restricting black carbon emissions on cargo shipping in the Polar Code Area.” Transportation Research Part A: Policy and Practice 147 (May 2021), 159-176. https://doi.org/10.1016/j.tra.2021.02.017.




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