Characterizing Aggregated Exposure to Primary Particulate Matter: Recommended Intake Fractions for Indoor and Outdoor Sources

Exposure to fine
particulate matter (PM2.5) from indoor
and outdoor sources is a leading environmental contributor to global
disease burden. In response, we established under the auspices of
the UNEP/SETAC Life Cycle Initiative a coupled indoor-outdoor emission-to-exposure
framework to provide a set of consistent primary PM2.5 aggregated
exposure factors. We followed a matrix-based mass balance approach
for quantifying exposure from indoor and ground-level urban and rural
outdoor sources using an effective indoor-outdoor population intake
fraction and a system of archetypes to represent different levels
of spatial detail. Emission-to-exposure archetypes range from global
indoor and outdoor averages, via archetypal urban and indoor settings,
to 3646 real-world cities in 16 parametrized subcontinental regions.
Population intake fractions from urban and rural outdoor sources are
lowest in Northern regions and Oceania and highest in Southeast Asia
with population-weighted means across 3646 cities and 16 subcontinental
regions of, respectively, 39 ppm (95% confidence interval: 4.3–160
ppm) and 2 ppm (95% confidence interval: 0.2–6.3 ppm). Intake
fractions from residential and occupational indoor sources range from
470 ppm to 62 000 ppm, mainly as a function of air exchange
rate and occupancy. Indoor exposure typically contributes 80–90%
to overall exposure from outdoor sources. Our framework facilitates
improvements in air pollution reduction strategies and life cycle
impact assessments.