A framework for estimating the US mortality burden of fine particulate matter exposure attributable to indoor and outdoor microenvironments

Abstract

Exposure to fine particulate matter (PM_2.5) is associated with increased mortality. Although epidemiology studies typically use outdoor PM_2.5 concentrations as surrogates for exposure, the majority of PM_2.5 exposure in the US occurs in microenvironments other than outdoors. We develop a framework for estimating the total US mortality burden attributable to exposure to PM_2.5 of both indoor and outdoor origin in the primary non-smoking microenvironments in which people spend most of their time. The framework utilizes an exposure-response function combined with adjusted mortality effect estimates that account for underlying exposures to PM_2.5 of outdoor origin that likely occurred in the original epidemiology populations from which effect estimates are derived. We demonstrate the framework using several different scenarios to estimate the potential magnitude and bounds of the US mortality burden attributable to total PM_2.5 exposure across all non-smoking environments under a variety of assumptions. Our best estimates of the US mortality burden associated with total PM_2.5 exposure in the year 2012 range from ~230,000 to ~300,000 deaths. Indoor exposure to PM_2.5 of outdoor origin is typically the largest total exposure, accounting for ~40-60% of total mortality, followed by residential exposure to indoor PM_2.5 sources, which also drives the majority of variability in each scenario.

Keywords: criteria pollutants; epidemiology; exposure modeling; inhalation exposure; particulate matter.

Fig. 1

Frequency distributions of the total annual US PM_2.5 mortality burden estimated by Monte Carlo simulations of microenvironmental exposures to PM_2.5 of both indoor and outdoor origin using three cases in Scenario 1, including sampling residential indoor concentrations from: a RIOPA-only, b MESA-only, and c from RIOPA and MESA equally (i.e., 50/50 RIOPA/MESA). The approximate curve fit is a lognormal distribution and summary statistics (median and interquartile range) are provided in units of deaths per year

Fig. 2

Distributions of the estimated contributions of microenvironmental exposures to PM_2.5 of indoor and outdoor origin to total PM_2.5 exposures across the US population using the three Scenario 1 cases: sampling residential indoor concentrations from a RIOPA-only, b MESA only, and c RIOPA and MESA equally (i.e., 50/50 RIOPA/MESA). Boxes represent 25th and 75th percentile values (i.e., interquartile range, or IQR); horizontal line represents median values; whiskers represent upper and lower adjacent values (i.e., 50% beyond the IQR)

Fig. 3

Best estimates of the number of annual deaths in the US associated with exposure to PM_2.5 of indoor and outdoor origin in each microenvironment in Scenarios 1 and 2