Field observations made with unmanned aerial vehicles of the particulate matter (PM) concentration from the ground to a height of 500 m were conducted at Xiaotang and Tazhong in the Taklimakan Desert (TD), China, from 7 to 15 November 2019. The vertical structures of the PM concentrations were studied. Pulsed lidar observations showed that dust aerosols in the TD can reach heights of 4 km. Within 500 m above the ground, the PM_1.0, PM_2.5, and PM₁₀ concentrations were <100, <201, and <764 µg∙m⁻³, respectively, in the TD. On days containing sand-blowing periods (e.g., at 18:00 on 11 November), the PM_1.0, PM_2.5, and PM₁₀ concentrations were 10–17.7 times higher than on clear days. The northern margin of the TD (Xiaotang) was dominated by fine particles, while the hinterland (Tazhong) was dominated by coarse particles, because there was sparse vegetation around Xiaotang and the surface was sand and clay, while there was no vegetation around Tazhong and the surface was sand. During floating dust periods, the boundary layer was dominated by fine particles. The average PM_1.0/PM_2.5 ratios were 0.25–0.65 and 0.40–0.80 at Tazhong and Xiaotang, respectively, while, during sand blowing periods, these ratios were 0.40–0.55 and 0.40–0.45, respectively. The critical condition in the atmospheric boundary layer for PM concentration was revealed with the enhanced momentum flux and sensible heat flux up to 0.52 kg∙m⁻¹∙s⁻², 0.69 m∙s⁻¹, and 6.7 W∙m², respectively, and the low mixed layer was high in the lower atmosphere.

The variation of solar radiation has a profound effect on the surface energy balance and hydrological cycle. Although the relationship between solar radiation variation and its influencing factors has been extensively studied, they are seldom used in Xinjiang, the largest province in China. In this study, we investigated the spatial distribution and temporal variation in global radiation (Eg), water vapor content (WVC), aerosol optical depth (AOD), total cloud cover (TCC), and low-level cloud cover (LCC) in Xinjiang, northwestern China, between 1961 and 2015. The annual average Eg reported at all stations was 5126.36252.8MJ·m⁻² with a mean of 5672MJ·m⁻². The highest annual mean E_g of 6252.8MJ·m⁻² occurred in Hami, eastern Xinjiang, whereas the lowest annual mean E_g of 5126.3MJ·m⁻² occurred in Urumqi, northern Xinjiang. The annual E_g variation was mainly affected by WVC, AOD, TCC, and LCC. Decreases in annual, spring, summer, autumn, and winter E_g trends were recorded in Xinjiang at rates of 33.88×10⁻², 1.92×10⁻², 1.89×10⁻², 3.47×10⁻², and 3.56×10⁻²MJ·m⁻²·decade⁻¹, respectively, with decreasing ratios of 9.43, 5.85, 0.14, 8, and 20.55, respectively. Increasing trends in annual WVC, AOD, TCC, and LCC were noted in Xinjiang at rates of 7.12×10⁻⁵mm·decade⁻¹, 2.74×10⁻⁶ decade⁻¹, 8.77×10⁻⁵ decade⁻¹, and 5.73×10⁻⁵ decade⁻¹, respectively. In addition, increasing trends in the annual E_g at Yining and Yanqi stations were observed. The E_g spatial distribution was complex in Xinjiang at the stations observed in this study, which were divided into six groups. E_g at group 1 showed an increasing trend associated with decreases in the WVC and TCC, whereas decreases in E_g were observed at groups 26, which could have been influenced by increases in AOD, TCC, and LCC.

Reactive gases (O₃, CO, NO₂, and SO₂) were collected hourly at the Akedala regional background station in northwestern China during September 2017 to August 2018. Wind rose, cluster analysis, potential source contribution function (PSCF), and concentration-weighted trajectory (CWT) methods were adopted for identifying the transport pathways and potential source regions of these atmosphere components at Akedala. The average O₃, CO, NO₂, and SO₂ mixing ratios detected were 29.65±11.44ppb, 123.78±73.35ppb, 3.79±0.98ppb, and 4.59±0.88ppb during the observation period, and the statistical results of the monthly mean values revealed that there were differences during the highest pollution period, with O₃ and CO mainly peaking in February, with mixing ratios of 38.03±7.10ppb and 208.50±106.50ppb, respectively. Meanwhile, NO₂ peaked in March (4.51±0.54ppb) and SO₂ in January (5.70±1.92ppb). The most obvious diurnal variation of CO and SO₂ was observed in the winter, with maximum levels reaching between 13:00 and 14:00. The diurnal variations of O₃ exhibited low values during the night and maximum values in the afternoon (16:0018:00). Diurnal variation was not significant in the case of NO₂. Cluster analysis showed that six main paths affected the Akedala atmosphere. In turn, the PSCF and CWT analysis results indicated that the Akedala reactive gas was affected by both local and foreign sources. The high PSCF value of the reactive gas potential source areas appeared in eastern Kazakhstan, northern Xinjiang, Western Mongolia, and Southern Russia. The WCWT (weighted concentration-weight trajectory) values of CO and SO₂ in winter were the highest, totaling 180240ppb and 56.5ppb, respectively. The WCWT value of O₃ in the spring and summer was higher than that in the autumn and winter. The main source area of O₃ was about 3236ppb in the spring and summer, and the main source area of NO₂ in the summer had a low WCWT value of 33.5ppb, whereas the NO₂ WCWT value was concentrated at 44.5ppb in the other seasons.

An observational data set of the year 2010 at a site in the northern marginal zone of the Taklimakan Desert (TD) was used to analyse the key surface parameters in land–atmospheric interactions in the desert climate of northwest China. We found that the surface albedo (α) and emissivity (ε) were 0.27 and 0.91, respectively, which were consistent with the values obtained based on observations in the hinterland of the TD as well as being similar to the dry parts of the Great Basin desert in North America, where they were comparable to the α and ε values retrieved from remote sensing products. Peak frequency value of z_0m was 5.858 × 10⁻³ m, which was similar to the Mojave Desert, Peruvian desert, Sonoran Desert, HEIFE (Heihe region) Desert, and Badain Jaran Desert. The peak frequency value of z_0h was 1.965 × 10⁻⁴ m, which was different from those obtained in the hinterland of the TD. The average annual value of excess resistance to heat transfer (kB⁻¹) was 2.5, which was different from those obtained in the HEIFE Gobi and desert, but they were similar to those determined for the Qinghai–Tibetan Plateau and HAPEX-Sahel. Both z_0m and z_0h varied less diurnally but notably seasonally, and kB⁻¹ exhibited weak diurnal and seasonal variations. We also found that z_0m was strongly influenced by the local wind direction. There were many undulating sand dunes in the prevailing wind and opposite to the prevailing wind, which were consistent with the directions of the peak z_0m value. The mean values calculated over 24 h for C_d and C_h were 6.34 × 10⁻³ and 5.96 × 10⁻³, respectively, which were larger than in the Gobi area, hinterland of the TD and semiarid areas, but similar to HEIFE desert. Under the normal prevailing (NNE–ESE) wind, the mean bulk transfer coefficient C_d and C_h were of the same order of magnitude as expected based on similarity theory. Using the data obtained under different wind directions, we determined the relationships between C_d, C_h, the wind speed U, and stability parameter z/L, and the results were different. C_d and C_h decreased rapidly as the wind speed dropped below 3.0 m s⁻¹ and their minimum values reached around 1–2 m s⁻¹. It should also be noted that the ε values estimated using the sensible heat flux (H) were better compared with those produced using other estimation methods.