Short-term ambient PM_2.5 exposure and cause-specific mortality in Massachusetts: Effect modification by structural...

Air exchange rate (AER) is a ventilation factor determining the infiltration of ambient air pollution indoors. AER has been under-examined as a source of air pollution health effect heterogeneity. Therefore, we assessed parcel-level structural AER as a modifier of the association between short-term ambient PM_2.5 exposure and cause-specific mortality in Massachusetts.

In this time-stratified case-crossover study, we included 770,836 nonaccidental deaths between 5 January 2000 and 31 December 2015. We examined the association between short-term ambient PM_2.5 and risk of cause-specific death with conditional logistic regression. Effect modification by seasonal parcel-level AER was examined with a season-specific AER and PM_2.5 product term, and stratification on parcel housing and residential type.

PM_2.5 in the preceding 2 days (lag 0-1) was associated with overall and cardiovascular mortality. Effect modification by AER was only observed in the warm season for all-cause and respiratory mortality. During the warm season among multifamily parcels, we observed the strongest effect modification by AER for respiratory mortality (odds ratio of interaction term: 1.15, 95% confidence interval [CI]: 1.05, 1.27). This corresponds to effect estimates per a 10 μg/m³ increase in PM_2.5 at the 25th percentile of AER (0.27/hour) that is associated with a 0.3% decrease in respiratory mortality (95% CI: -5%, 4%), and an 8.2% increase of respiratory mortality at the 75th percentile of AER (0.85/hour) (95% CI: 2%, 15%).

Parcel-level AER was a modifier of the association between short-term ambient PM_2.5- and mortality during warm seasons. Parcel-level AER may help us to better quantify associations between pollution and health outcomes.