Tropospheric Ozone in Southeast Asia: Budget and Mitigation Strategies – OSEAMS

On regional and global scales, tropospheric ozone is a key compound controlling atmospheric oxidation capacity and an important driver of climate change. On a local scale, ozone is a criteria air pollutant that has detrimental effects on human health and natural ecosystems. Although having successfully lowered some ozone precursor concentrations, many countries have been struggling to also lower ozone concentrations due to its rapid and complex photolytic formation chemistry and regionally transported plumes. Consequently, the Intergovernmental Panel on Climate Change (IPCC) Sixth Assessment Report (AR6) projects significant ozone increases across much of Southeast Asia (SEA) in the coming decades. Unlike other criteria pollutants, ozone is not emitted directly from various anthropogenic activities, but formed as a byproduct of volatile organic compound oxidation in the presence of nitrogen oxides and sunlight, making it challenging to design effective mitigation strategies. While chemical transport models are commonly used to investigate how ozone concentrations will change in response to precursor emission regulations, these models are at the whim of the embedded chemical and physical processes and emission inventories, and alternative methods to aid in the design of the mitigation strategies are needed in a field where important socio-economical aspects are at stake.

The research proposed in OSEAMS centers around the recently developed novel technique in France to measure Ozone Production Rates (OPR), which is a useful metric to investigate the atmospheric ozone budget, i.e. distinguishing between local in situ production and long-distance transport, and to gauge the effectiveness of mitigation regulations. This project seeks to transfer this knowledge to an area of the world in need of slowing down or turning around increasing ozone concentrations. In order to design an optimal roadmap for mitigating ozone in Taiwan, and ultimately in SEA and much of the rest of the world, we propose to (1) identify major production pathways of locally-formed ozone and distinguish it from transported O3 pollution in Taiwan, and then (2) assess ozone mitigation strategies implemented in Taiwan and other SEA countries. Specific tasks are to (i) build an OPR instrument in Taiwan, (ii) conduct an observation-based investigation of the ozone budget – through the deployment of both Taiwan and France OPR instruments at contrasting sites in Taiwan, (iii) characterize the ozone-forming chemistry – conducting simulation chamber experiments to describe the ozone chemistry and characterize the OPR response to mitigation measures, and (iv) assess past, current and future mitigation measures implemented in Taiwan and propose optimized reduction strategies. 0-D/3-D atmospheric modelling will support the field- and laboratory-based studies, and the assessment and improvement of ozone mitigation strategies. An originality of this work lies in using observation-based O3 budgets to drive mitigation strategies on this highly-populated pollution hotspot.

Taiwan will be used as an open laboratory to (1) assess the potential of real-time in situ measurements of the ozone budget for air quality monitoring networks and (2) design ozone mitigation roadmaps that will directly benefit policymakers of Taiwan, France and other countries to achieve lower ozone pollution levels in a context of climate change.