Aerosol direct radiative forcing is strongly dependent on aerosol distributions and aerosol types. A detailed understanding of such information is still missing at the Alpine region, which currently undergoes amplified climate warming. Our goal was to study the vertical variability of aerosol types within and above the Vipava valley (45.87 degrees N, 13.90 degrees E, 125 m a.s.1.) to reveal the vertical impact of each particular aerosol type on this region, a representative complex terrain in the Alpine region which often suffers from air pollution in the wintertime. This investigation was performed using the entire dataset of a dual-wavelength polarization Raman lidar system, which covers 33 nights from September to December 2017. The lidar provides measurements from midnight to early morning (typically from 00:00 to 06:00 CET) to provide aerosol-type dependent properties, which include particle linear depolarization ratio, lidar ratio at 355 nm and the aerosol backscatter Angstrom exponent between 355 nm and 1064 nm. These aerosol properties were compared with similar studies, and the aerosol types were identified by the measured aerosol optical properties. Primary anthropogenic aerosols within the valley are mainly emitted from two sources: individual domestic heating systems, which mostly use biomass fuel, and traffic emissions. Natural aerosols, such as mineral dust and sea salt, are mostly transported over large distances. A mixture of two or more aerosol types was generally found. The aerosol characterization and statistical properties of vertical aerosol distributions were performed up to 3 km.

The lack of light-absorbing aerosols vertical distributions data largely limited to revealing the formation mechanism of severe haze pollution in Chinese cities. Based on the synchronous measurements of size-resolved carbonaceous aerosols and meteorological data at near surface level and hilltop (about 620 m above the valley) in Lanzhou of northwest China, this study compared organic and elemental carbon (OC, EC) size distributions at the two altitudes and revealed the key influencing factors in a typical urban valley, China. The winter OC size distributions were typically bimodal with two comparable peaks in the accumulation and coarse modes, while those in summer were unimodal with the highest value in the size bin of 4.7-5.8 mu m. The size-resolved OC and EC at near the surface were significantly higher than those at the hilltop. The difference (concentrations and size distributions) of OC and EC between the surface and hilltop in summer was much smaller than that in winter due to stronger vertical mixing and larger summer SOC contributions at the hilltop. The winds paralleling with running urban valley were conducive to dispersing the air pollutants from near the surface to the upper air. The roles of horizontal and vertical dispersions to carbonaceous aerosols were comparable at near the surface, while horizontal dispersion was more important at the hilltop. Furthermore, the vertical dispersion was a main factor controlling size-resolved carbonaceous aerosols under highly polluted conditions in a typical urban valley. This study will provide the basis for regulation of severe haze pollution over complex terrain.