After the 2021 Air Quality Guidelines (AQGs): a scoping review study protocol on air pollution

BACKGROUND: Outdoor air pollution is a known risk factor for human health. In 2021, the World Health Organization (WHO) updated its former guidelines on air quality, considering the latest body of evidence (up to 2018) about health impact of different air pollutants. Yet, according to the WHO, some issues are well-covered, while others need further investigation. This scoping review is part of the “Air and Health” monitoring and research project promoted by Emilia-Romagna, a region of Italy located in the Po valley, the area with the highest concentration of air pollutants in Western Europe. It will summarize the literature produced after 2018 regarding long-term (LT) health effects of outdoor air pollution, describing whether recent studies are focused on reinforcing established results or on emerging topics. METHODS: The review follows the PRISMA extended for Scoping Reviews (PRISMA-ScR). We will conduct an online search on databases (Pubmed, EMBASE), reviewing the strings against the PRESS 2015 Evidence-Based Checklist. The eligibility criteria are: relation to outdoor air pollution and its LT effects on human health (excluding occupational setting), original research, any language (abstract in English), date of publication between 2019/01/01 and 2023/04/30. Further studies may be identified through reference crosscheck. Two authors will independently conduct the title/abstract screening, excluding the non-eligible reports via reference management software. In case of disagreement, a decision will be taken through consensus. Included articles will be summarized according to pollutant-outcome pairs investigated: confirmatory (pairs included in AQGs) or innovative (pairs not included in AQGs). RESULTS: The preliminary search string identified more than 1000 papers to be screened. CONCLUSIONS: The review will provide an insight in recent literature directions, whether it is confirmatory or innovative, to find possible gaps in the light of research needs identified by AQGs. KEY MESSAGES: • Outdoor air pollution is a risk factor for human health, but uncertainties still remain. • A review of the literature after the 2021 WHO global AQGs can orient future investigations.