A Case-Crossover Analysis of the Association between Exposure to Total PM_2.5and Its Chemical Components and Emergency Ambulance Dispatches in Tokyo

A limited number of studies have investigated the association between short-term exposure to PM_2.5components and morbidity. The present case-crossover study explored the association between exposure to total PM_2.5and its components and emergency ambulance dispatches, which is one of the indicators of morbidity, in the 23 Tokyo wards. Between 2016 and 2018 (mean mass concentrations of total PM_2.513.5 μg/m³), we obtained data, from the Tokyo Fire Department, on the daily cases of ambulance dispatches. Fine particles were collected at a fixed monitoring site and were analyzed to estimate the daily mean concentrations of carbons and ions. We analyzed 1038301 cases of health-based all-cause ambulance dispatches by using a conditional logistic regression model. The average concentrations of total PM_2.5over one and the previous day were positively associated with the number of ambulance dispatches. In terms of PM_2.5components, the percentage increase per interquartile range (IQR) increase was 0.8% for elemental carbon (IQR = 0.8 μg/m³95% CI = 0.3-1.3%), 0.9% for sulfate (2.1 μg/m³0.5-1.4%), and 1.1% for ammonium (1.3 μg/m³0.4-1.8%) in the PM_2.5-adjusted models. This is the first study to find an association between some specific components in PM_2.5and ambulance dispatches.