1. Introduction

Emission sources, environment fate, health effects and climate impacts of black carbon (BC) are increasingly concerned by the public and policy makers. BC, or soot, as a distinct type of carbonaceous material that strongly absorbs incoming solar radiation, is emitted by incomplete combustion of carbon fuels, such as coal, petroleum, biofuels and biomass. BC is widely found in the environment, including soils, ices, sediments, and the air. It was found that BC makes up 12–31 % of the sedimentary organic materials at two deep ocean sites, which has an age of thousands of years (Masiello and Druffel 1998). During the industrial-era, the consumption of fossil fuels and biofuels have been increased rapidly, leading to a significant increase of BC emissions to the atmosphere (Novakov et al. 2003; Ito and Penner 2005; Dentener et al. 2006; Bond et al. 2007; McConnell et al. 2007; He and Zhang 2009; Hirdman et al. 2010; Skeie et al. 2011). With a lifetime spanning from 1 to 10 days (Penner et al. 1993), BC can contribute to air pollution as a component in fine particulate matter (Brimblecombe 1987). The climate impact of BC, in addition to its impact on human health, has been recognized and highlighted in recent decades (Andreae 1995; Haywood and Shine 1995; Hansen et al. 1998; Myhre et al. 1998; Penner et al. 1998; Jacobson 2001b; Hansen and Nazarenko 2004). Now, BC has been widely concerned for its dual role in air pollution and climate change (Anenberg et al. 2012; Shindell et al. 2012).