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Balloon sounding with the Compact Optical Backscatter Aerosol Detector (COBALD) and Frost Point hygrometers (FPs) provides in situ data for a better understanding of the vertical distribution of cirrus clouds. In this study, eight summer balloon‐borne measurements in Kunming (2012, 2014, 2015, and 2017) and Lhasa (2013, 2016, 2018, and 2020) over the Tibetan Plateau were used to show the distribution characteristics of cirrus clouds. Differences of cirrus occurrence were compared by different indices: the backscatter ratio (BSR) at a 455 nm/940 nm wavelength (BSR455 > 1.2/BSR940 > 2), the color index (CI > 7), and the relative humidity with respect to ice (RHice > 70%). Analysis of the profiles indicated that BSR455 > 1.2 was the optimal criterion to identify the cirrus layer and depict the distribution of the CI and RHice within cirrus clouds. The results showed that the median CI (RHice) within the cirrus clouds at both sites was mostly in the 18–20 (90%–110%) range at pressures below 120 hPa. Furthermore, the balloon‐borne measurements combined with Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) measurements indicated a high frequency of cirrus occurrence near the tropopause in Kunming and Lhasa. The top height of cirrus occurrence at both sites was above the cold point tropopause and the lapse rate tropopause. Both Kunming and Lhasa had the highest frequency of thin cirrus clouds in the 0–0.4 km vertical cirrus thickness range. Plain Language Summary: Balloon‐borne measurements of cirrus clouds are scarce over the Tibetan Plateau. The sounding water vapor, ozone, and particles (SWOP) campaign has collected Compact Optical Backscatter Aerosol Detector (COBALD) and Frost Point Hygrometers (FPs) data for eight summers in Kunming and Lhasa. The backscatter ratio at wavelengths of 455 and 940 nm (BSR455, BSR940) from COBALD, the color index (CI), and the relative humidity over ice (RHice) from the FPs are able to indicate the occurrence of cirrus clouds. BSR455 >1.2/BSR940 > 2 was the optimal criterion to identify the cirrus layer in the upper troposphere over the Tibetan Plateau. The results showed that the CI and RHice within the cirrus clouds at both sites have a consistent distribution. The median CI (RHice) remained essentially in the range of 18–20 (90%–110%) below 120 hPa. The top height of cirrus occurrence at both sites was above the cold point tropopause and the lapse rate tropopause. Thin cirrus clouds (less than 400 m thick) had the highest frequency in both Kunming and Lhasa. Key Points: A backscatter ratio over 1.2/2 at a 455 nm/940 nm wavelength can effectively identify cirrus clouds over the Tibetan PlateauCirrus clouds were observed above the cold point tropopause (CPT) in both Kunming and LhasaAbout 38% (39%) of the cirrus clouds are thinner than 400 m in Kunming (Lhasa) [ABSTRACT FROM AUTHOR]

The Tibetan Plateau (TP), a region with limited human activity, is sensitive to regional and global climate change. In recent decades, surface observations have shown that concentrations of air pollutants (CO, NO2, SO2, and PM2.5) in Lhasa, a city on the TP, are similar to those in regions with high anthropogenic emissions (e.g., Eastern China). This study utilized the WRF‐Chem model and observational datasets to evaluate the concentrations and sources of air pollutants in Lhasa during August 2016. Our results show that the WRF‐Chem model with the standard emission inventory underestimated the surface concentrations of CO, SO2, and PM2.5 in Lhasa from 3 August 2016, 0:00 to 15 August 2016, 23:00 (UTC +8) by 59%, 92%, and 79%, respectively. Sensitivity simulations show that the contribution of long‐range transport of air pollutants from Eastern China and India is less than 10% for Lhasa. Insufficient emissions are found to be the main reason for the model's underestimation of air pollutants in Lhasa. Our study suggests that the emissions of CO, SO2, and PM2.5 in Lhasa in August 2016 might be underestimated by 85%, 93%, and 88%, respectively. Local anthropogenic emissions have a significant impact on urban air quality on the TP and deserve further attention. Plain Language Summary: The Tibetan Plateau (TP), a region with limited human activity, is sensitive to regional and global climate change. In recent decades, surface observations show that concentrations of air pollutants (CO, NO2, SO2, and PM2.5) in Lhasa City on the TP are similar to those in heavily polluted regions (e.g., Eastern China). The regional chemistry transport model (WRF‐Chem) with the standard emission inventory underestimated the surface concentrations of CO, SO2, and PM2.5 in Lhasa in August of 2016 by 59%, 92%, and 79%, respectively. Our study found that the contribution of long‐range transport of air pollutants from Eastern China and India is less than 10% for Lhasa city. Our study suggests that the main reason for the model's underestimation of the air pollutants in Lhasa is insufficient emissions in the standard inventory and the emission of CO, SO2, and PM2.5 in Lhasa in August 2016 might be underestimated by 85%, 93%, and 88%, respectively. Local anthropogenic emissions have a significant impact on urban air quality on the TP and deserve further attention. Key Points: The default model underestimates the concentrations of CO, SO2, and PM2.5 in Lhasa by 59%, 92%, and 79%The current emission inventory may underestimate the emissions of CO, SO2, and PM2.5 in Lhasa by more than 80%Urban air quality on the Tibetan Plateau deserves further attention for air pollution control [ABSTRACT FROM AUTHOR]

In situ measurements of vertically resolved particle size distributions based on a tethered balloon system were carried out for the first time in the highland city of Lhasa over the Tibetan Plateau in summer 2020, using portable optical counters for the size range of ​​​​​​​0.124–32 µ m. The vertical structure of 112 aerosol profiles was found to be largely shaped by the evolution of the planetary boundary layer (PBL), with a nearly uniform distribution of aerosols within the daytime mixing layer and a sharp decline with the height in the shallow nocturnal boundary layer. During the campaign, mass concentrations of particulate matter smaller than 2.5 µ m in aerodynamic diameter (PM 2.5) within the PBL ranged from 0.5 to 12.0 µ g m -3 , with an average and standard deviation of 3.4 ± 2.3 µ g m -3 , almost 4 times the amount in the free troposphere (FT), which was rarely affected by surface anthropogenic emissions. Though there was a lower level of particle mass in the residual layer (RL) than in the PBL, a similarity in particle mass size distributions (PMSDs) suggested that particles in the RL might be of the same origin as the particles in the PBL. This was also consistent with the source apportionment analysis based on the PMSDs. In total, three distinct modes were observed in the PMSDs for the PBL and the RL. One mode was exclusively coarse particles up to roughly 15 µ m, peaking around 5 µ m. More than 50 % of total particle mass was often contributed by coarse-mode particles in this area, which was thought to be associated with local dust resuspension. The mode peaking over 0.5–0.7 µ m was representative of biomass burning on religious holidays and was found to be most pronounced on holiday mornings. The contribution from the religious burning factor rose from about 25 % on non-holidays to nearly 50 % on holiday mornings. The mode dominated by particles smaller than 0.3 µ m was thought to be associated with combustion-related emissions and/or secondary aerosol formation. In the FT coarse mode, particles only accounted for less than 10 % of the total mass, and particles larger than 5 µ m were negligible. The predominant submicron particles in the FT might be related to secondary aerosol formation and the aging of existing particles. To give a full picture of aerosol physical and chemical properties and better understand the origin and impacts of aerosols in this area, intensive field campaigns involving measurements of vertically resolved aerosol chemical compositions in different seasons would be highly encouraged in the future. [ABSTRACT FROM AUTHOR]

To investigate the vertical distribution of volatile organic compounds (VOCs) concentrations in the Lhasa valley region, an intensive measurement campaign was first conducted in summer using a tethered balloon. The results showed that the average concentration of surface VOCs was 49.1 ± 30.1 ppbv, alkanes and aromatics were the main components. Notably, a very large discrepancy in VOCs was obtained between the wet (71.6 ± 25.9 ppbv) and dry (25.6 ± 8.0 ppbv) episodes, which was attributed to the atmospheric stability and diffusion capacity. Moreover, the total VOC (TVOCs) concentration declined under fluctuations, but it rapidly increased with height in the afternoon during the wet episode (2.50 ppbv/100 m, R2 = 0.47). According to the PMF results, combustion was the dominant emission source, additionally, the contribution of solvent coating in the wet episode and the background in the dry episode increased with height. Moreover, the O 3 concentration increased with height, and the decrease in L NOx-OH could effectively prevent the occurrence of high O 3 values. This study indicated that low wind speeds and high humidity levels highly likely cause the accumulation of atmospheric VOCs under static and stable conditions, while the control of high O 3 concentrations must still greatly consider summertime NOx emissions in Lhasa. [Display omitted] • Intensive vertical VOCs was firstly performed in Lhasa. • TVOCs concentration is 2.8 times higher in the wet episode in Lhasa. • Adverse diffusion factors caused VOCs accumulation in the wet episode. • The reduction in NOx could alleviate high-value O 3 pollution occurrence. [ABSTRACT FROM AUTHOR]

The structure of the tropopause transition layer (TTL) over the Asian summer monsoon (ASM) anticyclone is analyzed on the basis of high-resolution balloon soundings of temperature, ozone, and water vapor at Kunming and Lhasa, China during 11 summer monsoon seasons between 2009 and 2019. Two definitions of the TTL, one based on thermal structure and one based on tracer correlations of O 3 and H 2 O, are analyzed and compared. In tracer–tracer space, the air masses of mixed stratospheric and tropospheric characteristics are identified by using the O 3 –H 2 O correlations. The mixed air formed a transitional layer and shows strong spatial variation in the altitude space. Statistical result shows that the altitude range of mixed air parcels spans a layer of approximately 5.5 km depth between 12.5 km and 18 km. This vertical distribution of mixed air masses is basically consistent with thermally-based TTL, which takes the level of minimum stability (LMS) and the cold point tropopause (CPT) as its lower and upper boundaries, respectively. The thermal definition regards the TTL as a thermal transition zone, but does not consider the tracer mixing features between stratosphere and troposphere. Tracer correlations can identify the mixed air mass, which is a basic feature of the TTL, whether they are from the range of the thermally-based TTL, or below the LMS, or above the CPT. Based on the O 3 –H 2 O correlations, statistical analysis shows that about 30%–50% of air masses between the LMS and the CPT are identified as mixed. And up to 1–1.5 km above the CPT, a small fraction of air masses is also mixed, which means that air masses from the troposphere can be lifted and mixed into the free stratosphere within the ASM anticyclone region. • 11 years of high-resolution balloon measurements of temperature, ozone, and water vapor at Kunming and Lhasa were analyzed. • Two definitions of the TTL over the Asian summer monsoon (ASM) region, one based on thermal structure and one based on tracer relationships of O 3 and H 2 O, are analyzed and compared. • The altitude range of TTL over the ASM region spans a layer of approximately 5.5 km depth between 12.5 km and 18 km. • Based on the tracer–tracer correlations, about 30%–50% of air masses in the thermally-based TTL are identified as mixed. • A small fraction of air masses from the troposphere can be mixed up to 1–1.5 km above the cold point tropopase and into the lower stratosphere over the ASM anticyclone region. [ABSTRACT FROM AUTHOR]

We carried out field measurements of aerosols in Lhasa, a major city in the Tibetan Plateau that has been experiencing fast urbanization and industrialization. Aerosol number size distribution was continuously measured using an optical particle size spectrometer near the center of Lhasa city during the Asian summer monsoon season in 2016. The mass concentration of fine particles was modulated by boundary layer dynamics, with an average of 11 μg m −3 and the high values exceeding 50 μg m −3 during religious holidays. Daytime high concentration coincided with the religious burning of biomass and incense in the temples during morning hours, which produced heavy smoke. Factor analysis revealed a factor that likely represented religious burning. The factor contributed 34% of the campaign-average fine particle mass and the contribution reached up to 80% during religious holidays. The mass size distribution of aerosols produced from religious burnings peaked at ∼500 nm, indicating that these particles could efficiently decrease visibility and promote health risk. Because of its significance, our results suggest that further studies of religious burning, a currently under-studied source, are needed in the Tibetan Plateau and in other regions of the world where religious burnings are frequently practiced. [ABSTRACT FROM AUTHOR]