Tibetan Plateau (TP) has aroused widely scientific concerns in recent decades owning to its important effects on regional climatic and cryospheric changes, hydrological cycle, and environments. However, our understandings on the chemical and optical properties of aerosols are still limited at those regions. In this study, regional difference of aerosol light absorption properties were explored at three remote TP sites, including Qomolangma Station (QOMS) in the southern TP, Nam Co Station (NamCo) in the central TP, and Waliguan Observatory in the northeastern TP. Although aerosol mass concentration at QOMS was less than half of that at Waliguan, the light absorption coefficient at QOMS was nearly 5 time higher than that at Waliguan, mainly as a result of the high contributions of light-absorbing carbonaceous aerosols in the southern TP from the long-range transported biomass burning emissions of South Asia. An improved method was used to derive the near-realistic absorption Ångström exponent for pure black carbon (BC) particles. BC dominated the light absorption at all wavelengths, whereas brown carbon (BrC) contributed more than 30% of the light absorption at 370 nm at QOMS and ~ 20% at Waliguan and NamCo. The major contributor to BrC light absorption at QOMS was the biomass burning related organic aerosol. Radiative transfer simulations also showed the highest atmospheric radiative forcings at QOMS among the three campaigns. The significant regional differences of aerosol light absorption properties in the TP might be related tightly with the different aerosol sources and chemical processes.

In this study, we evaluated the variations of air quality in Lanzhou, a typical city in Northwestern China impacted by the COVID-19 lockdown. The mass concentration and chemical composition of non-refractory submicron particulate matter (NR-PM) were determined by a high-resolution aerosol mass spectrometry from January to March 2020. The concentration of NR-PM dropped by 40% from pre- to during control period. The five aerosol components (sulfate, nitrate, ammonium, chloride, and organic aerosol (OA)) were all decreased during control period with the largest from secondary inorganic species (70% of the total reduction), whereas the OA sources did not vary synchronously. OA from coal and biomass burning remained stably from pre- to during control period, while traffic and cooking related emissions were reduced by 30% and 50%, respectively. The production rates for secondary inorganic and organic aerosols were also evaluated and represented a decreased trend from pre- to during control periods.