Improvements in air quality over time provide
the backdrop for a “natural experiment” to examine
the potential beneficial health effects. As part
of the 20-year Children’s Health Study, three separate
cohorts of children have had longitudinal
lung-function measurements recorded over the
same 4-year age range (11 to 15 years) and in the
same five study communities but during different
calendar periods. In this study, we examined
whether changes that have occurred across these
time spans in levels of nitrogen dioxide, ozone,
and particulate matter with an aerodynamic diameter
of less than 2.5 μm (PM2.5), less than 10 μm
(PM10), and between 2.5 and 10 μm (coarse particulate
matter [PM10–PM2.5]) are associated with
the development of lung function in children.