Air quality indexes: Key considerations and roadmaps for best practices

In response to a call by experts for WHO to promote health-based AQIs (29) and building on WHO’s recent work to support evidence-based risk communication (5,15,29–31), including at the country level (32), the current report aims to provide a comprehensive overview of AQIs from a public health perspective. The report focuses on health-based AQIs or AQHIs, including a review of existing practices, salient issues and key considerations to strengthen their implementation. The main target audiences are authorities in charge of providing air quality information to the public, as well as technical experts, health-care professionals and researchers in the field of air quality.

A structured approach was applied to guide the development of this report, combining a targeted review of the literature, critical appraisal by an expert writing group, and an external review process. The expert writing group had expertise in atmospheric science, clinical medicine, communication, environmental epidemiology, health policy, population health and toxicology. The evidence base was compiled through a PubMed search for peer-reviewed literature conducted in October 2024 using relevant search terms, supplemented by grey literature, including WHO reports and other key documents identified by the expert writing group. Relevant papers were summarized to capture current practices and key considerations, with the aim of informing a roadmap for best practices. Insights from the expert writing group were incorporated throughout the process through structured email exchanges and virtual meetings. A preliminary draft of the report underwent external review by experts and stakeholders, who contributed additional perspectives in areas such as environmental engineering and behavioural science. Their feedback was assessed and incorporated where appropriate. Throughout the report, the Canadian AQHI, the United Kingdom’s daily AQI and the United States AQI were often highlighted as illustrative examples because they were (among) the first official indexes in their respective categories, have long records of real-world use and have more extensively informed research and development efforts.

The report is organized into three further chapters: Chapter 2 provides a review of the science related to AQ(H)Is, Chapter 3 contains key considerations and roadmaps to enhance current practices, and Chapter 4 contains concluding remarks.