Towards compliance with the 2021 WHO air quality guidelines: A comparative analysis of PM2.5 trends in australia and china

In 2021, the World Health Organization (WHO) released new Air Quality Guidelines (AQG) which significantly reduced the recommended annual mean concentration of fine particulate matter (PM2.5) in ambient air from 10 mu g/m3 (AQG 2005) to 5 mu g/m3 (AQG 2021). Recent studies have shown that this challenging new target may be close to or even below the background levels of PM2.5 resulting from non-anthropogenic activities in many regions globally, such as areas affected by desert dust. This raises an important question: can countries achieve compliance with the new guideline for PM2.5? Here we investigated this question from the perspective of two countries that fall on opposite ends of the spectrum of ambient air pollution. We examined historical PM2.5 trends based on observations of annual mean PM2.5 concentrations from 2013 to 2024 in eight capital cities of each state in Australia and 31 capital cities of each province in mainland China. A statistical model was used to differentiate the contributions of meteorological variations and anthropogenic drivers to determining the annual trends of PM2.5 concentrations. Subsequently, we analyzed and discussed the feasibility of meeting the guidelines for each city based on these results. Our findings demonstrate that compliance with the new guideline is largely achievable, or has the potential to be achieved, in more than half of the cities in Australia. Notably, there is a high probability that a city, after meeting the guideline, may return to the non-compliance again. In addition, in some cities, eliminating anthropogenic emissions may not lead to a significant further reduction in PM2.5 concentrations, and they might not achieve compliance. In contrast, PM2.5 concentrations are an order of magnitude higher in some cities in China, yet Lhasa holds the potential to become the first Chinese city to meet the guideline in the future. Meeting the new AQG is highly challenging for Chinese cities, and even if achievable, it will take a long time. However, it is certain that China still has significant potential for further reductions in PM2.5 concentrations. This can be achieved through the ongoing implementation of emission control measures and the transition to the use of new sources of energy to reduce anthropogenic emissions. This study provides insights into the development of city-specific policies for air pollution control and management in both Australia and China.