Surface ozone pollution over the Tibet, China: Characteristics, drivers, and source analysis.

Area of Science:

• Atmospheric Chemistry
• Environmental Science
• Air Quality Research

Background:

• The Tibetan Plateau faces persistent surface ozone (O3) pollution despite low emissions.
• Altitude-dependent influences and drivers of O3 under low-emission conditions are not well understood.

Purpose of the Study:

• Investigate the spatiotemporal characteristics, vertical structure, and driving mechanisms of O3 pollution in Tibetan cities.
• Quantify the altitude-dependent impacts of emissions and meteorology on O3.

Main Methods:

• Utilized a backpropagation artificial neural network (BP-ANN) coupled with a numerical air quality model (WRF-CAMx).
• Conducted meteorological analyses, BP-ANN simulations, scenario-based emission reduction experiments, and Process Analysis (PA).

Main Results:

• Surface O3 peaks in spring with significant spatial heterogeneity and weak intercity coupling.
• Boundary layer development and solar radiation show seasonally nonlinear effects on O3, enhancing spring concentrations.
• O3 formation is predominantly NOx-limited, with modest reductions (15-30 μg/m³) from local emission removal.
• Near-surface O3 is more controllable locally, while upper layers are influenced by stratospheric intrusion and regional transport.

Conclusions:

• Ozone pollution on the Tibetan Plateau has unique, altitude-dependent formation mechanisms and drivers.
• Nonlinear meteorological effects and regional/stratospheric transport are critical factors, with limited local emission control effectiveness for upper-level O3.
• Findings offer new insights into O3 controllability and nonlinear drivers in high-altitude regions.