Sensitivity of climate effects of black carbon in China to its size distributions

The climate effects of black carbon (BC) aerosols are sensitive to BC size distributions and this sensitivity over China is studied using a regional climate model, namely RIEMS2.0. A new size-resolved scheme is developed based on observational data. The simulated BC concentrations with the new scheme are better compared with the observation than the previous uniform scheme, which is likely to overestimate BC concentrations, radiative forcings, and warming effects in many regions of China due to its simple assumption on BC size. The simulation with the size-resolved scheme suggests a reduction of the all-sky radiative forcing of BC at the top of atmosphere (TOA) by 0-0.25 W m− 2 over the most study domain. Correspondingly, the warming effect of BC is weakened by − 0.04 to − 0.16 K over most parts of South China and North China. The difference in BC-induced precipitation between the two schemes varies irregularly from region to region, ranging from − 2.8 to 2.8 mm d− 1. With the size-resolved scheme, the BC radiative properties and the climate effects are reassessed and the means (ranges) over the study domain are summarized as follows. The annual mean surface concentration of BC is 0.88 μg/m3, ranging from 1 to 8 μg/m3 over North China and Central China. The all-sky and clear-sky radiative forcings of BC at the TOA are 0.43 and 0.39 W/m2, respectively. Over most parts of Southwest China, Central China, and North China, the BC warming effect prevails, with enhanced temperature of 0.04-0.28 K. BC aerosols usually enhance precipitation in South China and North China, ranging from 0.40 to 2.8 mm d− 1.