The optical properties of urban aerosol in northern China: A case study at Xi'an

• Simultaneous measurements of particle scattering coefficient (Bscat) and absorption coefficient (Babs) were conducted at Xi'an.
• Based on the Ångström coefficients, anthropogenic fine particles show dominant contribution during the sampling period, accompanied by occasional dust events.
• A conceptual equation for visibility degradation in Xi'an was established.

Simultaneous measurements of particle scattering coefficient (Bscat) and absorption coefficient (Babs) were conducted at Xi'an from mid-August to mid-October 2012 to estimate the particle single scattering albedo (SSA) and the Ångström coefficients in highly polluted urban air. The hourly averaged Bscat was 272 Mm− 1 at 532 nm and 82 Mm− 1 at 870 nm, while hourly averaged Babs was 31 Mm− 1 at 532 nm and 19 Mm− 1 at 870 nm. Similar diurnal variations for Bscat and Babs were observed between the two wavelengths. The averaged SSA was 0.88 at 532 nm and 0.78 at 870 nm. Based on the Ångström coefficients, anthropogenic fine particles show dominant contribution during the sampling period, accompanied by occasional dust events. Moreover, the major contributors to aerosol optical properties are attributed to the mixture of black carbon (BC) and brown carbon (BrC) with non-absorbing components over urban area in northern China. The findings provide useful insights into the factors affecting the visibility in northern Chinese cities and therefore essential knowledge for improving the air quality.