How emission control policies deliver synergetic climate and environmental health benefits in transportation sector

The research team, led by Professor Yixuan Zheng from the Chinese Academy of Environmental Planning (CAEP), has developed a policy-specific assessment framework featuring a novel Synergy Index to evaluate the integrated effects of emission control policies on greenhouse gas mitigation, air quality improvement, and public health protection. Their findings show that China’s on-road transportation emission control policies have achieved remarkable progress during 2010-2020, but their synergies have been weakening, underscoring the urgent need for deep structural transitions to sustain effective carbon and air-pollution co-control.

Air pollution and climate change have long been managed through separate policy tracks, even though both originate from the same fossil fuel-based energy system that warms the planet and pollutes the air. In recent years, China has made “GHG-emission and air-pollution co-control” a central strategy for high-quality development, shifting national governance from single-objective control to integrated management of air pollutants and greenhouse gases. Clean air actions and carbon mitigation policies have achieved remarkable progress, yet single policies rarely deliver both goals. Policymakers are now turning to combinations of multiple policies to pursue stronger multiple benefits, but there has been less unified framework that consistently quantifies both health and climate dimensions to capture the full spectrum of synergies and trade-offs in designing GHG and air pollution co-control policy.

To address this challenge, the team developed a policy-specific synergetic level analysis framework that integrates a detailed bottom-up emission inventory, a chemical transport model, an epidemiological concentration-response model, and a customized Synergy Index within a unified system. Applying this framework to China’s on-road transportation sector, the researchers found that China’s on-road environmental policies reduced GHG emissions (i.e., covering CO₂ and black carbon) by 427 Mt CO₂e and averted 104,000 premature mortality during 2010-2015, but these gains declined to 278 Mt CO₂e and 72,000 premature mortality in 2015-2020, making the Synergy Index declined from 0.75 to 0.61 during the two periods. Policy-specific evaluations reveal that traditional policies like tightening emission standards and fuel quality and removing high-emitting vehicles drove early synergies. Conversely, emerging structural transitions, including promoting electric vehicles and modal shift from road to more efficient modes, grew in prominence but failed to offset declining efficacy. Strategic optimization of vehicle fleet and transportation structure to meet 2025 targets could reverse this decline trend. These findings underscore the urgency of accelerating structural transitions to sustain effective carbon and pollution co-control in transportation sector, with global relevance for fossil fuel-dependent economies. The framework further revealed that reductions in short-lived climate pollutants such as black carbon would have delivered strong near-term air-quality and climate benefits, helping reinforce the momentum toward long-term decarbonization.

“It’s like seeing the hidden mechanics of policy synergies for the first time,” explained lead author, CAEP’s Zhulin Qi.

“Our framework acts as a diagnostic tool, revealing which actions truly work together and where new opportunities lie,” Yixuan Zheng said. “By assessing different policies and their combinations within one system, we can observe the overall effectiveness of different policy combinations and the specific focus of individual policies, making it possible to identify those that achieve true synergies.”

The policy-specific framework and Synergy Index offer policymakers a science-based tool to advance carbon and air pollution co-control and contributes a valuable “China experience” to the world’s pursuit of sustainable development.

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