Limitations include the assignment of PM2.5 data to study participants at a coarse geographic scale, at the level of the MSA of residence at enrollment, rather than at the individual- or household-level.
Previous research in the CPS-II examining mortality health effects at the intraurban scale in Los Angeles, California, revealed relative risk estimates approximately threefold greater than those estimated using between-city contrasts (47).
There was also limited historical PM2.5 monitoring data, with widespread systematic PM2.5 monitoring occurring only in the late 1990s, nearly two decades after cohort enrollment.
Air pollution exposures experienced over an extended historical time period are likely more relevant to the etiology of lung cancer than air pollution exposures experienced in the more recent past (7, 29).
Although PM2.5 concentrations have declined in recent decades, with an approximate in 33% decline in mean PM2.5 concentrations observed from 1979–1983 to 1999–2000 in the 53 MSAs with data available on both time periods, PM2.5 data from both historical monitoring time periods were strongly correlated (r >0.7) and the relative ranking of MSAs in terms of PM2.5 concentrations was generally retained over time.
Similar findings for lung cancer mortality were also observed using either PM2.5 (1979–1983) or PM2.5 (1999–2000) among participants residing in one of the 53 MSAs common to both measures (fully adjusted HR per each 10 μg/m3 PM2.5 [1979–1983] = 1.16, 95% CI 0.99–1.35; PM2.5 [1999–2000] = 1.15, 95% CI 0.89–1.48).