Although air pollution is known to be a major risk factor for poor health outcomes, research on the relationship between air pollution and emphysema progression is lacking. Researchers conducted a study in six U.S. metropolitan areas from 2000 to 2018 to determine whether long-term exposure to air pollutants was associated with the progression of emphysema and a decline in lung function in a multiethnic cohort of adults.

The study included a total of 6,860 participants. Spatiotemporal exposure models based on measurements from the U.S. Environmental Protection Agency Air Quality System were used to estimate long-term exposure to ozone, fine particulate matter, and oxides of nitrogen in each study region; mean outdoor concentrations of black carbon were also estimated, but only for two years of the study. Participants were followed for a median of 10 years. Results were adjusted for a range of variables, including body mass index, smoking status and pack-years, and secondhand smoke exposure.

Outcomes were measured in relation to baseline exposure levels and exposure over the years of follow-up. At baseline, median percent emphysema (that is, the percentage of emphysema-like lung on computed tomographic scan) was 3%, and the mean rate of change was 0.58 percentage points over 10 years. At baseline, airflow obstruction was present in a subset of participants. Over 10 years, their mean decline was 309 mL in forced expiratory volume in the first second and 331 mL in forced vital capacity.

Annual mean levels of fine particulate matter and oxides of nitrogen declined over the years of follow-up, but ozone levels did not. Greater exposure to ozone, fine particulate matter, and oxides of nitrogen at baseline-and to black carbon from 2006 to 2008-were all significantly associated with greater increases in the progression of percent emphysema, as were higher concentrations of ozone and oxides of nitrogen during the years of follow-up. The authors note that the increased progression of emphysema secondary to ozone exposure was equal to that of 29 pack-years of smoking.

The authors point out that outdoor air pollution levels don't necessarily reflect individual air pollution exposures and dose. In addition, they conclude, outdoor levels don't explain all variations in indoor concentrations.