Vertical distributions of aerosol optical properties during the spring 2016 ARIAs airborne campaign in the North China Plain

Vertical distributions of aerosol optical properties derived from measurements made during 11 aircraft flights over the North China Plain (NCP) in May–June 2016 during the Air Chemistry Research In Asia (ARIAs) were analyzed. Aerosol optical data from in situ aircraft measurements show good correlation with ground-based measurements. The regional variability of aerosol optical profiles such as aerosol scattering and backscattering, absorption, extinction, single scattering albedo (SSA), and the Ångström exponent (α) are thoroughly characterized for the first time over the NCP. The SSA at 550 nm showed a regional mean value of 0.85 ± 0.02 with moderate to strong absorption and the α ranged from 0.49 to 2.53 (median 1.53), indicating both mineral dust and accumulation-mode aerosols. Most of the aerosol particles were located in the lowest 2 km of the atmosphere. We describe three typical planetary boundary layer (PBL) scenarios and associated transport pathways as well as the correlation between aerosol scattering coefficients and relative humidity (RH). Aerosol scattering coefficients decreased slowly with height in the clean PBL condition, but decreased sharply above the PBL under polluted conditions, which showed a strong correlation (R2 ≥ 0.78) with ambient RH. Back-trajectory analysis shows that clean air masses generally originated from the distant northwestern part of China, while most of the polluted air masses were from the heavily polluted interior and coastal areas near the campaign region.