Temporal variations of short-term associations between PM10 and NO2 concentrations and emergency department visits in Shanghai, China 2008-2019.

Levels and constituents of ambient air pollution have substantially changed in China over the last decade. Such changes may lead to the variations in health effects of air pollution. Very limited studies, however, have investigated the temporal variations in health effects of air pollution on a long-term scale, especially in China. We evaluated the temporal variations in short-term associations between PM10 and NO2 concentrations and emergency department (ED) visits during a 12-year period from 2008 to 2019 in Shanghai, China. A quasi-Poisson generalized linear regression was performed to assess the associations between PM10 and NO2 concentrations and ED visits during entire study period and three specific periods. We evaluated the temporal variations of period-specific associations with an interaction variable between pollutant concentrations and period indicators. We further investigated the concentration-response relationships for specific periods. The effects on specific subpopulations (males and females; 18-65 years old and >65 years old) were also examined. A 10 μg/m3 increase of PM10 and NO2 corresponded to 0.48% (95% CI: 0.36%, 0.59%) and 1.51% (95% CI: 1.25%, 1.78%) increase in ED visits at lag0-7 day for entire study period, respectively. The short-term associations between ED visits and NO2 remained unchanged over time (P-value > 0.05), while the effects from PM10 were significantly inconsistent (P-value < 0.05), with the highest effect observed during the intermediate period of 2012-2015 and the lowest effect observed during the initial period of 2008-2011. Similar temporal trends were found in subgroups, except for elderly group. Despite substantial reduction in ambient PM10 and NO2 concentrations, the short-term effects on ED visits for NO2 remained stable and even increased for PM10. More efforts were needed to reduce harmful components in air pollution mixture to reduce the health hazards of air pollution.