What has driven the ozone increase in Hong Kong over the past decade under stringent air pollution control?

  • 呂效譜, Xiaopu (PI)
  • Blake, Donald R. (External CoI)
  • CHATANI, Satoru (External CoI)
  • Guo, Hai (External CoI)
  • Wang, Hao (External CoI)

Project: Research project

Project Details


Ground-level ozone (O3) has been increased in many regions of China including HK in recent decades, imposing increasingly negative impacts on air quality, human health, and climate. The increase has even been unintentionally accelerated since 2013, due to the nationwide implementation of the Clean Air Action Plan, as well as meteorological variations. Conversely, it is inferred with a few pieces of evidence that O3 in the
continental outflows from China mainland stopped increasing or even began to decrease.

In HK, air pollution control was started in early 2000s and has been continued to the present. Previous studies including those conducted by the project team examined the changes in O3 and the precursors resulting from certain control measures. However, most of the study periods were only up to 2013/2014. In recent years, the measures to tackle air pollution were extended and strengthened, such as phasing out high-emission
diesel vehicles, setting caps of sulfur content for vessel fuels, reducing emissions of power plants, and controlling the contents of volatile organic compounds in solvent products. A handful of studies confirmed the effectiveness of some measures in reducing
primary air pollution, but the impacts on O3 air quality are unknown.

At least, what we can see from the continuous monitoring data is that O3 kept increasing in HK in the recent decade. It is well documented that O3 pollution in this city relates to not only local emission and chemistry but also regional transport (outflows from China mainland), especially in autumn, and is sensitive to meteorology. Now that national and local air pollution controls were intensively implemented from 2013/2014 onwards, and they failed to curb the rise in HK’s O3 levels, it is therefore essential to solve the puzzle: What has driven the recent O3 increase in HK?

With this project, we will find the answer to this question. In brief, the research focuses on determining the recent variations of meteorology-corrected O3 concentrations in HK and upwind regions in autumn, examining the changes in chemical profiles of O3 precursors, elucidating the impacts of the above changes on in-situ and transport photochemistry, and quantitatively understanding the roles of multiple drivers in modulating the recent O3 increase in HK.

The project will have strong policy implications with respect to effective O3 control and could become a paradigm for uncovering the mystery of rising O3 that is emerging in many places of the world.
Effective start/end date1/01/2431/12/26


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