Hypoxia and adverse health outcomes might be affected by O₃ pollution in the highland city of Lhasa. NO_x emissions can amplify the role of volatile organic compounds (VOCs) in the secondary production of O₃ under the conditions of high ultraviolet (UV) radiation levels and unfavourable dispersion patterns in the Lhasa River valley. Here, online C₂–C₁₁ VOC measurements, accompanied by other parameters concerning the O₃ chemical budget, were first obtained and employed to identify the key VOC species and key sources of VOCs in terms of the loss rate against OH radicals (L_OH), ozone formation potential (OFP), secondary organic aerosol potential (SOAP), and toxicity. Oxygenated VOCs (OVOCs) not only were the most abundant VOCs but also dominated L_OH, OFP, and toxicity. Isoprene and anthropogenic VOCs were further identified as precursors of these OVOCs. Aromatics accounted for 5 % of the total VOCs (TVOCs) but contributed 88 % to the SOAP and 10 % to the toxicity. As the primary oxidative intermediates of aromatics were not well characterized by our measurements, the environmental impact of aromatics could be underestimated by our data. Source appointment and ternary analysis of benzene, toluene, and ethylbenzene confirmed the combined contribution of traffic emissions, solvent usage, and biomass burning. This suggests that O₃ precursors are mainly from sources associated with residents' lives, except for solvent usage emissions which contribute to aromatics. Preliminary comparisons between source spectrums of transport sector emissions with positive matrix factorization (PMF)-decomposed ones and our measured ones suggest that vehicle emission patterns of VOCs at high altitude generally follow the ground-level impression. More quantitative data are required to further confirm this point though. Emission reduction strategy analysis for O₃ pollution control highlighted multiple benefits of the simultaneous reduction in NO_x originating from diesel vehicle emissions, biomass burning, and background sources (possibly dominated by incense burning). The notable biogenic emission contribution to the OFP was also first confirmed in our study, and this highlights the side effects of the government's pursuit of a greener city.

New particle formation (NPF) is an important source of cloud condensation nuclei (CCN), which affects Earth's radiative balance and global climate. The mechanism and CCN contribution of NPF at the high-altitude mountains, especially in the Tibetan Plateau (TP), was unclear due to lack of measurements. In this study, intensive measurements were conducted at the Nam Co station (4730 m a.s.l.) in the central TP during both the pre-monsoon and summer monsoon seasons. The frequencies of NPF events exhibited evident seasonal differences with 15 % in the pre-monsoon season and 80 % in the monsoon season. The comprehensive analysis of the measured condensation sink (CS), gaseous precursors and meteorological conditions, supplemented by the model simulations of SO₂ and volatile organic compound (VOC), points to the organic involved nucleation as the dominant mechanism. Condensation sink and gaseous sulfuric acid could have no significant effect on the occurrence of NPF events. The frequent NPF events in the summer monsoon season may result from the higher frequency of southerly and southwesterly air masses, which brought the organic precursors to participate in the NPF process. It had increased the aerosol number concentrations and CCN at supersaturation of 1.2 % by more than 2 and 0.6 times compared with those in the pre-monsoon season, respectively. Considering that the smaller particles formed by NPF may further grow and reach CCN size during the following days due to the low-level coagulation sink, the amount of potential CCN in the monsoon season could be much larger than our local measurement results. Our results emphasized the importance of considering the seasonal effect of NPF when simulating the amounts of aerosols and CCN in the high-altitude atmosphere. Long-term investigations with a full set of instrumentation are required for deeper scientific understanding of NPF process and its role in the global budget in the TP.

Hygroscopic aerosols take up water and grow with increasing relative humidity (RH), giving rise to large changes in light extinction (b_ext), scattering (b_scat), absorption (b_abs), and single scattering albedo (SSA, ω). The optical hygroscopic growth factors for each parameter (f(RH)${}_{\mathrm{ext},\mathrm{scat},\mathrm{abs},\mathit{\omega }}$ ) are thus important for assessing aerosol effects on regional air quality, atmospheric visibility, and radiative forcing. The RH dependence of aerosol scattering and extinction has been studied in many laboratory and field studies. However, owing partly to the absence of suitable instrumentation, there are few reports of the RH dependence of aerosol absorption and ω. In this work, we report the development of a humidified cavity-enhanced albedometer (H-CEA) for simultaneous measurements of f(RH)${}_{\mathrm{ext},\mathrm{scat},\mathrm{abs},\mathit{\omega }}$ at λ=532 nm from 10 % to 88 % RH. The instrument's performance was evaluated with laboratory-generated ammonium sulfate, sodium chloride, and nigrosin aerosols. Measured hygroscopic growth factors for different parameters were in good agreement with model calculations and literature-reported values, demonstrating the accuracy of the H-CEA for measuring RH-dependent optical properties.

Vertical profiles of aerosol light scattering (b_scat), absorption (b_abs), as well as the single scattering albedo (SSA, ω), play an important role in the effects of aerosols on climate, air quality, and local photochemistry. High-precision in-situ measurements of the vertical profiles of these properties are challenging and therefore uncommon. We report here the development of a portable cavity-enhanced albedometer operating at λ = 532 nm for use aboard an unmanned aerial vehicle (UAV). Multi-optical parameters, b_scat, b_abs, extinction coefficient b_ext, and ω, can be measured simultaneously in the same sample volume. The achieved detection precisions in laboratory were 0.38, 0.21, and 0.43 Mm^-1 for b_ext, b_scat, and b_abs, respectively, for a 1 s data acquisition time. The albedometer was installed on an hexacopter UAV and simultaneous in-situ measurements of the vertical distributions of b_ext, b_scat, b_abs, and ω were realized for the first time. Here we report a representative vertical profile up to a maximum height of 702 m with a vertical resolution of better than 2 m. The UAV platform and the albedometer demonstrate good performance and will be a valuable and powerful tool for atmospheric boundary layer research.

Knowledge of aerosol radiative effects in the Tibetan Plateau (TP) is limited due to the lack of reliable aerosol optical properties, especially the single scattering albedo (SSA). We firstly reported in situ measurement of SSA in Lhasa using a cavity enhanced albedometer (CEA) at λ = 532 nm from 22nd May to 11th June 2021. Unexpected strong aerosol absorbing ability was observed with an average SSA of 0.69. Based on spectral absorptions measured by Aethalometer (AE33), black carbon (BC) was found to be the dominated absorbing species, accounting for about 83% at λ = 370 nm, followed by primary and secondary brown carbon (BrC _pri and BrC _sec ). The average direct aerosol radiative forcing at the top of atmosphere (DARF ^TOA ) was 2.83 W/m ² , indicating aerosol warming effect on the Earth‐atmosphere system. Even though aerosol loading is low, aerosol heating effect plays a significant role on TP warming due to strong absorbing ability.