Evaluation of Ozone Smog Alerts on Actual Ozone Concentrations:A Case study in North Carolina

Ground-level ozone is an important pollutant regulated under the Clean Air Acts that affects respiratory morbidity, decreases lung function, and negatively affects those with existing respiratory conditions like asthma. This study examines the “Clean Air Works” program on ozone concentration levels, which is operating in Charlotte area of North Carolina State. “Clean Air Works” is a voluntary program which educates people about the negative effects of air pollution on health. Moreover, this program encourages people to reduce air pollution by using voluntarily alternative transportation modes, such as carpooling and public transit, especially when a smog ozone alert is issued. The contribution of this study is that it examines three effects: The effectiveness of the “Clean Air Works” program and whether ozone smog alerts are more effective under this program. Finally, the effects on ozone levels coming from the change in the warning threshold from 80 particles per billion (ppb) to 75 ppb, which took place in 2008, are established. For this purpose a quadruple Differences (DDDD) estimator is applied. In both cases, we find reduction in ground-level ozone levels and improvement of the air quality in the treatment group where the “Clean Air Works” program is implemented. In addition, the air quality is improved when smog alerts are associated with the program. Finally, taken additionally into consideration the change of the threshold at 75 ppb the air quality is improved by 1.5 ppb in the treatment group relatively to the control group. This study suggests that the ozone warning system associated with voluntary programs can help to clean the air and improve the public health.