Characterization of black carbon aerosol at the summit of Mount Tai (1534 m) in central east China: Temporal variation, source appointment and transport

Abstract

As a crucial absorption component of aerosols, black carbon (BC) plays a key role in modifying aerosol-planetary boundary layer (PBL) meteorology and hence aggravating haze pollution. With an altitude of 1534 m, Mt. Tai is close to the top of the PBL and located within the transportation channel from the North China Plain (NCP) to the Yangtze River Delta (YRD). In this study, BC aerosols were continuously observed using a seven-channel aethalometer (AE-33) at the summit of Mt. Tai from May 11 to June 25, 2017. The temporal variation, source and transport characteristics of BC in the upper PBL of central and eastern China in summer were then discussed. The average concentrations of BC, BC_liquid and BC_solid were 1722.6, 1194.6 and 545.8 ng m⁻³, respectively, during the observation period. Liquid fuel sources were calculated and accounted for 64.7% of the BC mass concentration. The distributions of BC were mostly centralized in concentrations less than 600 ng m⁻³ (accounting for 21.9% of the total BC samples) and ranged from 1400 to 2200 ng m⁻³ (32.5%). Meteorological elements were determined to have great impacts on the distribution of BC concentrations, which increased with the decrease in visibility and wind speed and the increase in relative humidity (RH). The diurnal variations in BC presented high values during the daytime and low values during the nighttime, with peaks at 06:00, 11:00 and 18:00. Long-range transport from the YRD regions in summer, as well as the surrounding regions, played an important role in determining the BC concentrations at Mt. Tai with concentration weighted trajectory (CWT) values exceeding 2000 ng m⁻³. Air masses may move northward to the NCP after passing through Mt. Tai, and they contributed more than 1800 ng m⁻³ to the BC in the whole NCP region.