After 40 years of fighting acid rain, Tsinghua University may finally win

China has achieved remarkable results in acid rain control, but ecological risks still need attention. Duan Lei's research group at the School of Environment at Tsinghua University systematically evaluated and prospected the effects and future paths of China's acid deposition control. The relevant results were published in the National Science Review (NSR) under the title "A probe into the acid deposition mitigation path in China over the last four decades and beyond".

This study combined the atmospheric chemical transport model with China's acid gas emissions and historical data on acid deposition over the past 40 years. Based on the updated critical load data, it comprehensively evaluated the changes in China's supercritical load of acid deposition over the past 40 years and in the future, and proposed a path for China to reduce the supercritical load of acid deposition in the future.

As of 2020, China's sulfur dioxide and nitrogen oxide emissions have dropped by 77% and 32% from their historical peaks in 2006 and 2012, respectively, achieving a faster reduction process than Europe and the United States. The area of ​​acid rain in China has dropped sharply from 40% in 2005 to 4.8% in 2020, and the annual average precipitation pH value has continued to improve and rebounded to above 5.6, reflecting the great achievements made in China's acid rain control. At the same time, China's acid deposition has been clearly decoupled from economic growth. Although China's total economic output has increased 5.4 times since 2005, air pollutant emissions have continued to decline, mainly due to a series of governance measures taken by China since 1998.

Acid rain trends and related variables in China, 1980-2020. Comparison of energy consumption, emissions, precipitation pH, and control policies with those in Europe (EU-28) and the United States.

Although acid gas emissions have dropped significantly, the research team found that the acidification and eutrophication risks of China's ecosystems have not been significantly reduced by calculating the critical load of soil and surface water. Even in the optimal emission reduction scenario of achieving air quality standards and climate change mitigation goals by 2035, 13% of the country still faces eutrophication ecological risks, 8.9% of the country faces soil acidification risks, and nearly a quarter of surface water headflow areas face acidification risks.

Supercritical loads with acid deposition. a. Distribution of soil acidification and ecosystem eutrophication under the 2005, 2015, 2022 and 2035-CBE scenarios. b. Supercritical loads on surface water. c. Supercritical load amounts.

Compared with Europe and the United States, China's ecosystems are less sensitive to acid deposition, but with the same amount of emission reduction, China's acidification ecological risk reduction is much smaller than that of Europe and the United States. Taking the peak acid deposition period as an example, the proportion of China's soil acidification risk area in 2005 (16%) was much lower than that of Europe (26%) and the United States (29%) around 1990. This is mainly because China's emission reduction strategy focuses on improving air quality, while European and American countries aim to protect ecosystems and use critical load as an important guide for emission reduction.

Based on this, the study designed a future emission reduction path with ammonia emission reduction as the core to reduce China's future ecosystem eutrophication risk. Since ammonia emissions are difficult to effectively control using terminal treatment technologies, ammonia emissions in the 2035 Paris Agreement air quality target scenario will only drop by 18% compared to 2015. The study suggests that if China further reduces ammonia emissions by 27% on the basis of the 2035 emission reduction scenario, the ecological impact of acid deposition can be basically eliminated around 2035, and more than 92% of the country will no longer face the risk of acidification and eutrophication, while reducing PM2.5 concentration by 12% compared to the CBE scenario.

The study emphasizes that China needs to take into account multiple environmental goals such as climate change, air quality and ecological benefits in future air pollution prevention and control, especially considering the sensitivity of ecosystems in different regions to acid deposition. This study not only provides important scientific support for China's future acid deposition control and policy formulation, but also provides reference for the acid rain control experience of other developing countries.

The research was led by Duan Lei's research group at the School of Environment at Tsinghua University, with the participation of Academician Hao Jiming and Wang Shuxiao's research group at Tsinghua University, Zhao Yu's research group at Nanjing University, and scientists from relevant European institutions.

For more details, please read the original article:

A probe into the acid deposition mitigation path in China over the last four decades and beyond
‍https://doi.org/10.1093/nsr/nwae007