Hourly associations between ambient air pollution and emergency ambulance calls in one central Chinese city: Implications for hourly air quality standards.

Most studies on the short-term health effects of air pollution have been conducted on a daily time scale, while hourly associations remain unclear.We collected the hourly data of emergency ambulance calls (EACs), ambient air pollution, and meteorological variables from 2014 to 2016 in Luoyang, a central Chinese city in Henan Province. We used a generalized additive model to estimate the hourly effects of ambient air pollutants (PM, PM, SO, and NO) on EACs for all natural causes and cardiovascular and respiratory morbidity, with adjustment for potential confounding factors. We further examined the effect modification by temperature, relative humidity, wind speed, and atmospheric pressure using stratified analyses.In the single-pollutant models, PM, PM, SO, and NO were associated with an immediate increase in all-cause morbidity at 0, 0, 12, 10 h, separately, after exposure to these pollutants (excess risks: 0.19% (95% confidence interval (CI): 0.03%, 0.35%), 0.13% (95% CI: 0.02%, 0.24%), 0.28% (95% CI: 0.01%, 0.54%) and 0.52% (95% CI: 0.06%, 0.99%), respectively). These effects remained generally stable in two-pollutant models. SO and NO were significantly associated with an immediate increase in risk of cardiovascular morbidity, but the effects on respiratory morbidity were relatively more delayed. The stratified analyses suggested that temperature could modify the association between PM and EACs, humidity and atmospheric pressure could modify the association between SO and EACs.Our study provides new evidence that higher concentrations of PM, PM, SO, and NO may have transiently acute effects on all-cause morbidity and subacute effects on respiratory morbidity. SO and NO may also have immediate effects on cardiovascular morbidity. Findings of this study have important implications for the formation of hourly air quality standards.