Outdoor air-pollution monitoring stations in each
of the study communities have been continuously
measuring regional air pollutants since 1994. Data
on hourly or daily concentrations of nitrogen dioxide,
PM2.5, PM10, and ozone were routinely collected
with Federal Reference Method or Federal
Equivalent Method instrumentation. A systematic
quality-assurance program was in place to
review all data. Mean air-pollutant concentrations
were calculated for each community over
the relevant periods of exposure for each cohort
(1994–1997 for cohort C, 1997–2000 for cohort
D, and 2007–2010 for cohort E)