When and where to exercise: An assessment of personal exposure to urban tropical ambient airborne pollutants in Singapore.

Background: Physical activity is associated with health benefits and has been shown to reduce mortality risk. However, exposure to high levels of ambient fine particulate matter (PM) during exercise can potentially reduce the health benefits of physical activity. This study aims to assess and compare the PM concentrations of different exercise venues in Singapore by their location attributes and time of day.

Methods: Personal PM exposures (μg/m) at 24 common outdoor exercise venues in Singapore over 49 sampling days were collected using real-time personal sensors from September 2017 to January 2020. Wilcoxon rank-sum test and Kruskal-Wallis test were used to compare PM concentrations between different timings (peak (0700-0900; 1800-2000) vs. non-peak (0600-0700; 0900-1800; 2000-2300); weekend vs. weekday), and location attributes (near major roads (<50 m) vs. away from major roads (≥50 m)). Multivariable linear regression models were used to assess the associations between location attributes, timings and ambient PM with personal PM concentration, adjusting for potential confounders.

Results: Compared with peak hours, exercising during non-peak hours was associated with a significantly lower PM exposure (median, 17.8 μg/m during peak vs. 14.5 μg/m during non-peak; P = 0.006). Exercise venues away from major roads have significantly lower PM concentrations as compared to those located next to major roads (median, 14.4 μg/m away from major roads vs. 18.5 μg/m next to major roads; P < 0.001). Individuals who exercised in parks experienced the highest PM exposure (median, 55.0 μg/m) levels in the afternoon during 1400-1500. Furthermore, ambient PM concentration was significantly and positively associated with personal PM exposure (β = 0.85, P < 0.001).

Conclusions: Our findings suggest that exercising outdoors in the urban environment exposes individuals to differential levels of PM at different times of the day. Further research should investigate a wider variety of outdoor exercise venues, explore different types of air pollutants, and consider the varying activity patterns of individuals.