Estimating the number of cardio-pulmonary events potentially averted by fine particulate matter air quality index activity guidelines

Background: Fine particulate matter <2.5 µm (PM_2.5) air pollution increases cardio-pulmonary morbidity and mortality. To inform the public regarding local air quality and reduce short-term exposures to PM_2.5, daily Air Quality Indices (AQIs) with activity guidance are issued across the United States (US). We aimed to estimate the cardio-pulmonary health benefits of the current AQI strategy. Methods: We estimated the number needed to treat (NNT) per county per day to avoid 1 atherosclerotic cardiovascular disease (ASCVD) or pulmonary event during each PM_2.5 AQI action day (defined as a day with an AQI >100 for PM_2.5) for 3 groups (healthy adults, ASCVD and pulmonary disease patients) in the US during 2022. The theoretical number of adverse events potentially prevented per county was estimated each day as the relevant county population divided by the corresponding NNT. These results were summed for all AQI action days among US counties to equal the potential total number of ASCVD and pulmonary events avoided nationwide. Results: There were 1081 AQI action days for PM_2.5 (58.0 ± 32.4 µg/m³) across 236 counties in 2022, accounting for an estimated excess of 164 ASCVD and 3963 pulmonary events. Approximately 31 ASCVD and 796 pulmonary events could be theoretically avoided if all populations followed activity guidelines during every AQI action day. Conclusions: Daily AQI activity guidelines, as currently structured and implemented, likely prevent few cardio-pulmonary events per year in the US. Additional research is warranted to determine how to improve the overall approach to more effectively protect public health.