Cointegration analysis of ambient ozone on respiratory disease prevalence in Southern California

Abstract The short- and long-run effects of ambient pollution—particularly surface ozone—on respiratory health are well documented. Ambient pollutants from agricultural, industrial, and vehicular sources are monitored by statewide and federal agencies, including the Environmental Protection Agency (EPA), the National Institutes of Health (NIH), and the California Air Resources Board (CARB). Elevated ozone levels are strongly associated with increased respiratory morbidity, especially chronic obstructive pulmonary disease (COPD). This study models the dynamic relationship between ambient ozone concentrations and monthly inpatient COPD diagnoses across three major Southern California counties. Using an autoregressive distributed lag (ARDL) framework with bounds testing procedures, the study assesses whether a cointegrating relationship exists between ozone levels and monthly COPD inpatient diagnoses. The final error correction model (ECMs) is constructed to access the rapid and persistent influence of ozone on respiratory health. Findings reveal a statistically significant cointegration relationship: after adjusting for seasonality and temporal trends, a 0.01 ppm increase in monthly average maximum ozone concentration corresponds to a 3.26% (95% CI: 0.84 ~ 5.73%) rise in monthly COPD diagnoses. Moreover, the estimated ECM coefficient indicates that approximately 46.5% (95% CI: 29.0~63.9%) of any disequilibrium is correlated within one month.