Short-term impacts of ambient fine particulate matter on emergency department visits: Comparative analysis of three exposure metrics

Abstract

Background: Research argued that daily excessive concentration hours (DECH) could be more informative through accounting for within-day variations, when assessing population-level exposure to ambient fine particle (PM2.5). However, few studies have comparatively investigated PM2.5-associated risks using DECH and two common metrics of daily mean and hourly peak concentration.

Methods: We collected daily records of all-cause emergency department visits (EDVs) and hourly data on air pollutants and meteorological factors from Shenzhen, China, 2015–2018. According to guidelines proposed by the World Health Organization, DECH was calculated by summing up daily concentrations exceeding 25 μg/m3. Based on time-stratified case-crossover design, we adopted conditional logistic regression models to assess short-term attributable risks of EDVs associated with PM2.5 using three exposure metrics.

Results: DECH and daily average of PM2.5 strongly elevated risks of EDVs, while less evident associations were observed using hourly peak metric. Estimated excess relative risks at lag 0 day were 0.56% (95% confidence interval [CI]: 0.21 to 0.91), 0.69% (95% CI: 0.25 to 1.13) and 0.37% (95% CI: 0.02 to 0.76), respectively, associated with an interquartile range increase in DECH (420.2 μg/m3), 24-h average (24.9 μg/m3) and hourly peak concentration (38 μg/m3). More emergency visits could be attributed to DECH than daily mean PM2.5, with attributable fractions of 2.02% (95% CI: 1.42 to 2.61) and 1.09% (95% CI: 0.69 to 1.49), respectively.

Conclusions: This study added evidence for increased risk of EDVs associated with exposure to ambient PM2.5. DECH was a potential alternative exposure metric for PM2.5 assessment, which may have implications for future revision of air quality standards.