Background Evidence suggests that particulate matter (PM) with smaller particle sizes (such as PM1, PM with an aerodynamic diameter≤1 µm) may have more toxic health effects. However, the short-term association between PM1 and asthma mortality remains largely unknown.

Objective This study aimed to examine the short-term effects of PM1 and PM2.5 on asthma mortality, as well as to investigate how neighborhood characteristics modified this association.

Methods Daily data on asthma mortality were collected from 13 cities in Jiangsu Province, China, between 2016 and 2017. A time-stratified case-crossover design was attempted to examine the short-term effects of PM1 and PM2.5 on asthma mortality. Individual exposure levels of PM1 and PM2.5 on case and control days were determined based on individual’s residential addresses. Stratified analyses by neighborhood characteristics (including green space, tree canopy, blue space, population density, nighttime light and street connectivity) were conducted to identify vulnerable living environments.

Results Mean daily concentrations of PM1 and PM2.5 on case days were 33.8 μg/m3 and 54.3 μg/m3. Each 10 μg/m3 increase in three-day-averaged (lag02) PM1 and PM2.5 concentrations were associated with an increase of 6.66% (95%CI:1.18%,12.44%) and 2.39% (95%CI: 0.05%−4.78%) asthma mortality, respectively. Concentration-response curves showed a consistent increase in daily asthma mortality with increasing PM1 and PM2.5 concentrations. Subgroup analyses indicated that the effect of PM1 appeared to be evident in neighborhood characteristics with high green space, low urbanization level and poor street connectivity.

Conclusion This study suggested an association between short-term PM1 and PM2.5 exposures and asthma mortality. Several neighborhood characteristics (such as green space and physical supportive environment) that could modify the effect of PM1 on asthma mortality should be further explored.