National and state air pollution controls that went into effect in the early have been linked to decreasing death rates from emphysema, asthma and pneumonia among people in North Carolina, according to a new study.

Using mortality trends from state public health data, along with monthly measurements from air-monitoring stations across North Carolina from 1993-2010, researchers from Duke University were able to draw a close association between improved air quality and declining death rates from respiratory illnesses.

"This research tends to show that environmental policies work, if the goal of those policies is not only to improve the environment, but also to improve health," said H. Kim Lyerly, senior author of the study.

For the study, researchers analyzed a 17-year period after a variety of federal air pollution measures were instituted. Using the public health and environmental monitoring data, and controlling for factors such as lower smoking rates and month-to-month fluctuations in air quality, the researchers calculated how each one-unit reduction in the air pollution components coincided with a drop in deaths from emphysema, asthma and pneumonia.

"In this study we applied the methods of ecologic analyses for health and environmental data collected at the county level and accounting for geographic and progressive changes," said Julia Kravchenko, co-author of the study and research scientist in the Department of Surgery at Duke University. "Specifically, we developed a model to predict seasonal variations of respiratory mortality rates in terms of monthly changes in air pollution levels and several other factors such as smoking during an almost 20-year period."

Among gaseous pollutants, reductions of sulfur dioxide levels showed significant correlation to lower death rates for emphysema, asthma and pneumonia; decreases in carbon monoxide were significantly associated with lower emphysema and asthma deaths. Fine particulates coincided with lower emphysema death rates, and reductions in a second particulate matter were associated with lower asthma deaths.

The researchers said other factors, in addition to better air quality, could also contribute to the drops in death rates from respiratory diseases.

The findings were recently published in the International Journal of COPD.