Arid Zone Research ›› 2025, Vol. 42 ›› Issue (11): 1994-2004.doi: 10.13866/j.azr.2025.11.04

• Weather and Climate • Previous Articles     Next Articles

Temperature profile characteristics of the northern slope of the Central Tianshan Mountains with the gradient distribution of altitude and its influence on air pollution

LIU Zonghui1,2(), LI Xia1,2(), CHENG Kai1,2, LI Shuting1,2, MU Huan3, LI Huoqing1,2, ZHONG Yuting1,2, Mauren AYIKAN1,2, XIA Xiangao4, FU Disong4   

  1. 1. Institute of Desert Meteorology, China Meteorological Administration, Urumqi 830002, Xinjiang, China
    2. Field Scientific Experiment Base of Akdala Atmospheric Background, China Meteorological Administration, Urumqi 830002, Xinjiang, China
    3. Xinjiang Uygur Autonomous Region Meteorological Observatory, Urumqi 830002, Xinjiang, China
    4. Laboratory of Middle Atmosphere and Global Environment Observation, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China
  • Received:2025-04-22 Revised:2025-06-26 Online:2025-11-15 Published:2025-12-13
  • Contact: LI Xia E-mail:liuzh@idm.cn;susannaryy@163.com

Abstract:

Urban agglomeration on the northern slope of the Central Tianshan Mountains ranks among the most serious air-pollution problems in China. The impact of temperature inversion over local complex terrain on air pollution has been poorly understood for many years. Here, we derive the wintertime temperature profiles from data obtained by triplicate ground-based microwave radiometers (MWRs) deployed along an elevational transect (613-935 m above sea level) in the Urumqi Valley, Middle Tianshan Mountains, from November 2023 to March 2024. Based on concurrent radiosonde profiles and air-quality monitoring data, we verify the vertical credibility of MWR temperature retrievals, analyze the elevational dependence of the temperature inversion characteristics, and relate the temperature inversion to pollution regime. The MWR and radiosonde data are consistent below 2000 m (R>0.94) and the MWR retrievals can capture the vertical evolution of temperature stratification. In winter, the temperature difference between the top and bottom of the inversion layer and the thickness of the inversion layer in the urban area from south to north increase by 2.1 ℃ and 186 m, respectively, for each 100 m decrease in altitude. Diurnal evolution shows that nocturnal surface-based inversions dominate the valley with maximum inversion at 08:00 Beijing time (top-to-bottom temperature difference of ΔT=9.1℃; inversion layer thickness=1300 m) at low-elevation sites. Post-sunrise, southern Urumqi experiences inversion dissipation while the central and northern sections of the city experience elevated and surface-based inversions, respectively, indicating post-sunrise heterogeneity. As the air quality index (AQI) rises from grade I to grade IV, the thickness of the inversion layer, ΔT, and intensity of the temperature inversion synchronously increase at different altitudes. The ΔT increases by 2-6 ℃. At AQI of grade V or higher, the above inversion parameters slightly decrease from those at grade IV. This change indicates that temperature inversion on the northern slope of the Tianshan Mountains aggravates the pollution problem. The most serious stage of pollution may be contributed by additional factors such as regional transport and chemical transformation.

Key words: gradient distribution, temperature profile, temperature inversion, air pollution, the northern slope of the Central Tianshan Mountains