Short-term effects of air pollution on mortality have been well documented in the literature worldwide.
Less is known about which subpopulations are more vulnerable to air pollution. We conducted a caseonly
study in Hong Kong to examine the potential effect modification by personal characteristics and
specific causes of death. Individual information of 402,184 deaths of non-external causes and daily mean
concentrations of air pollution were collected from 2001 to 2011. For a 10 mg/m3 increase of pollution
concentration, people aged V65 years (compared with younger ages) had a 0.9e1.8% additional increase
in mortality related to PM, NO2, and SO2. People dying from cardiorespiratory diseases (compared with
other non-external causes) had a 1.6e2.3% additional increase in PM and NO2 related mortality. Other
subgroups that were particularly susceptible were females and those economically inactive. Lower socioeconomic
status and causes of cardiorespiratory diseases would increase the likelihood of death
associated with air pollution.