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.