Columnar optical properties of locally emitted light-absorbing carbonaceous aerosols

The vertical distribution of light-absorbing carbonaceous aerosols significantly affects atmospheric radiative forcing properties. A novel method combining HYSPLIT trajectory ensemble and concentration-weighted trajectory (CWT) analysis (Ens-HYSPLIT-CWT) was employed in this study to distinguish local emission events from all air mass sources. The aerosol profile distribution under pollution control measures in Beijing was investigated using continuous and simultaneous measurements at both surface and mountain stations. By applying the wavelength dependence of the absorption Ångström exponent (WDA) method, more accurate brown carbon (BrC) absorption coefficients at 370 and 470 nm were derived, better aligning with the observed wavelengths of the AE33 instrument. We found a larger vertical decrease for BrC compared to black carbon (BC) particles, resulting in an enhanced fraction of BC absorption relative to BrC measured at the mountain station. Furthermore, we investigated the columnar aerosol optical properties at 550 nm by combining BC and BrC absorption, and aerosol scattering properties derived from Mie theory. Peak values of aerosol optical depth (AOD) and absorption aerosol optical depth (AAOD) both occurred at noon during locally emitted pollution events. AOD increased by 1.91 times, and AAOD increased by 1.93. Additionally, due to the higher transport efficiency of BC particles compared to non-BC particles during locally emitted pollution events, the single scattering albedo (SSA) exhibited a valley at noon.