Revising the ambient air quality standards for SO2 in China: A comprehensive analysis of air quality trends, health impacts, and global alignment.

China has achieved remarkable progress in reducing sulfur dioxide (SO₂) emissions, largely attributable to rigorous control measures on coal consumption. However, the nation's ambient air quality standards (AAQS) for SO₂ have not been updated for over 40 years, rendering them outdated and inadequate to address the evolving SO2 concentration characteristics and meet the growing public demand for enhanced air quality. This study undertook a comprehensive evaluation and revision of China's AAQS for SO₂ by analyzing historical atmospheric SO2 concentration data collected from national monitoring stations across the country between 2019 and 2023, assessing the potential health benefits of revised standards and comparing them with international standards. Results indicate that atmospheric SO2 concentrations at over 98 % of monitoring sites are consistently below the primary standard for the 24-h average (50 µg/m³), with SO₂ concentrations remaining under 25 µg/m³ in the past two years. Despite this progress, seasonal fluctuations and regional variations persist, with higher concentrations observed in winter months and in northern cities. Compared to international standards, China's secondary limits remain less stringent. To better align with global benchmarks and enhance public health outcomes, this study recommends revising the 24-h and annual average SO₂ concentrations limits to 40 µg/m³ and 15 µg/m³ for primary standard and 50 µg/m³ and 20 µg/m³ for secondary standard, respectively. These revisions could deliver substantial health benefits, particularly in regions with high pollution levels. The findings of this study provide robust scientific evidence supporting the urgent need for updated AAQS for SO₂ in China, ensuring the reduced limits align with global best practices while promoting significant health and environmental benefits.