Mortality-Air Pollution Associations in Low Exposure Environments (MAPLE): Phase 2

Mortality is associated with long-term exposure to fine particulate matter (particulate matter ≤2.5 μm in aerodynamic diameter; PM ), although the magnitude and form of these associations remain poorly understood at lower concentrations. Knowledge gaps include the shape of concentration-response curves and the lowest levels of exposure at which increased risks are evident and the occurrence and extent of associations with specific causes of death. Here, we applied improved estimates of exposure to ambient PM to national population-based cohorts in Canada, including a stacked cohort of 7.1 million people who responded to census year 1991, 1996, or 2001. The characterization of the shape of the concentration-response relationship for nonaccidental mortality and several specific causes of death at low levels of exposure was the focus of the Mortality-Air Pollution Associations in Low Exposure Environments (MAPLE) Phase 1 report. In the Phase 1 report we reported that associations between outdoor PM concentrations and nonaccidental mortality were attenuated with the addition of ozone (O ) or a measure of gaseous pollutant oxidant capacity (O ), which was estimated from O and nitrogen dioxide (NO ) concentrations. This was motivated by our interests in understanding both the effects air pollutant mixtures may have on mortality and also the role of O as a copollutant that shares common sources and precursor emissions with those of PM . In this Phase 2 report, we further explore the sensitivity of these associations with O and O , evaluate sensitivity to other factors, such as regional variation, and present ambient PM concentration-response relationships for specific causes of death. PM concentrations were estimated at 1 km spatial resolution across North America using remote sensing of aerosol optical depth (AOD) combined with chemical transport model (GEOS-Chem) simulations of the AOD:surface PM mass concentration relationship, land use information, and ground monitoring. These estimates were informed and further refined with collocated measurements of PM and AOD, including targeted measurements in areas of low PM concentrations collected at five locations across Canada. Ground measurements of PM and total suspended particulate matter (TSP) mass concentrations from 1981 to 1999 were used to backcast remote-sensing-based estimates over that same time period, resulting in modeled annual surfaces from 1981 to 2016. Annual exposures to PM were then estimated for s