Historical variation in black carbon deposition and sources to Northern China sediments

Black carbon (BC) in fine particulate matter (PM_2.5) is an important air pollutant in a large area of China. We have reconstructed a 100-year-long history of BC deposition based on analyses of sediment samples in the coastal area of the Northern China Plain (NCP). During 1900-2010, the sedimentary BC concentrations at three cores increased from 0.2 to 1.3, from 0.2 to 2.3, and from 0.2 to 1.9 mg g^-1, and the ranges for the BC deposition fluxes were 0.1-4.7, 0.1-8.2, 0.2-7.4 g m^-2 a^-1, suggesting the increase of ten times from the pre-industrial era. The BC deposition fluxes showed abrupt variation with two peaks in the 1970s and 2010s. Residential energy consumption and biomass burning (i.e., low-temperature combustion sources; thus, large-scale wildfires with high temperature may not be included) were responsible for the BC increase in the 1970s. Fossil fuel combustion generated by the industrial sectors, including industry, power plants, and transportation, was negligible before 1990 but significantly increased during 1990-2010. The historical increase in the BC deposition was accurately predicted by climate models, specifically the Coupled Model Intercomparison Project Phase 5 (CMIP5). However, the BC fluxes in the NCP sediments were an order of magnitude greater than those of the simulated depositions, suggesting an underestimation of the BC deposition in the severely polluted area in China.