环境中的黑碳及其全球生物地球化学循环

BLACK CARBON IN THE ENVIRONMENTS AND ITS GLOBAL BIOGEOCHEMICAL CYCLE

黑碳是生物物质或化石燃料燃烧产生的难熔物质的连续统一体,从焦化植物残体、木炭到烟炱,以及石墨态黑碳,组成了黑碳的3种主要类型。它们的理化性质变化很大,焦化植物残体和木炭主要在低温下形成;烟炱是高温气态物质浓缩形成;而石墨态黑碳可能是岩石成因的。黑碳的分解主要是光化学分解和微生物降解。黑碳在全球碳循环中占有重要的位置。每年燃烧可产生50~270 Tg黑碳,其中约 10%来源于化石燃料燃烧。细小的黑碳在大气中被搬运到远离燃烧地的土壤或海洋中沉积下来,在沉积物有机碳中占有很大的比例。从地质历史时期看,它对于大气圈中CO2、O2的含量演化有重要影响。本文将黑碳的分析测量方法归纳为 5 类:显微镜法、光学法、热氧化法、化学方法和分子标志物法。同时指出当今黑碳研究中需要一种标准参考物,黑碳的测量应进一步细化到分子水平,并加强不同类型黑碳的全球生物地球化学循环过程研究。

Black carbon (BC) is defined as the broad continuum of recalcitrant materials produced from biomass burning to fossil fuel combustion. From charred plant residues and charcoal to soot and graphitic black carbon, the chemical and physical properties of this recalcitrant material vary broadly. The charred plant residues and charcoal formed at low temperatures; soot formed during the condensation of hot combustion gases; and graphitic black carbon may have a rock-derived source. There are two mechanisms, photochemical and microbial breakdown, for BC degradation. BC may represent a significant sink in the global carbon cycle. Annual global formation rates for black carbon were estimated to be 50~270 Tg (10^(12)g), among which about 10% may come from fossil fuel combustion. Fine black carbon can be transported a long distance and deposited in soils and sediments, building up a significant fraction of organic carbon buried in soils and sediments. BC may put a great influence on the content of atmospheric CO_(2 )and O_(2 )over geological time scales. BC analytical methods were categorized into five classes: microscopic, optical thermal, chemical, thermal, and molecular markers. We discuss challenges for future research, and point out that standard reference materials are urgently needed, BC analysis should be further defined into molecular level, and the research of global geochemical cycle of different types of BC should be enhanced.