Engagement in outdoor physical activity under ambient fine particulate matter pollution: A risk-benefit analysis

Background: Outdoor physical activity (PA) brings important health benefits, but exposure to polluted air increases health risks. This study aimed to quantify the tradeoff of PA under fine particulate matter (PM _2.5) air pollution by estimating the optimal PA duration under various pollution levels. Methods: A risk-benefit analysis was performed to estimate the optimal outdoor moderate-intensity PA (MPA) duration under varying PM _2.5 concentrations. Results: An inverse nonlinear relationship was identified between optimal MPA duration and background PM _2.5 concentration levels. When background PM _2.5 concentration increased to 186 µg/m ³, the optimal outdoor MPA duration decreased to 2.5 h/week, the minimum level recommended by current PA guidelines. When background PM _2.5 concentration further increased to 235 µg/m ³, the optimal outdoor MPA duration decreased to 1 h/week. The relationship between optimal MPA duration and background PM _2.5 concentration levels was stronger when exercising at a location closer to a source of air pollution. Compared to the general adult population, adults aged 60 years and older had substantially steeper curves—the optimal outdoor MPA duration decreased to 2.5 h/week when background PM _2.5 concentration reached 45 µg/m ³. Conclusion: The health benefit of outdoor MPA by far outweighs the health risk of PM _2.5 pollution for the global average urban background concentration (22 μg/m ³). This modeling study examined a single type of air pollutant and suffered from measurement errors and estimation uncertainties. Future research should examine other air pollutants and indoor PA, incorporate short- and mid-term health effects of MPA and air pollution into the risk-benefit analysis, and provide estimates specific for high-risk subgroups.