Effect of air pollutant emission reduction policies on hospital visits for asthma in Seoul, Korea; Quasi-experimental study.

To improve air quality and reduce adverse health effects due to air pollutants, Seoul metropolitan government has introduced emission reduction policies in Seoul metropolitan area since 2007. As a result, air quality in Seoul has improved. However, no study has reported whether emission reduction policies have affected respiratory morbidities in Korea. Thus, we aimed to assess an association between air pollutant emissions and ambient concentrations, and the effect of implemented emission reduction policies on asthma. The population of Daejeon, one of the metropolitan cities in Korea other than Seoul was used as a reference population to adjust for possible long-term background trend. Trends of air pollutant emissions, ambient concentrations, and hospital visit rates in Seoul and Daejeon were evaluated using descriptive statistics. To evaluate the possible beneficial effect of air pollutant emission reduction policies implemented since 2007 on hospital visits for asthma in Seoul, we conducted interrupted time-series analysis. As a result, we found evidence for the association between emission reductions and reduced ambient concentrations. Trends in hospital visit rates for asthma, which were previously increasing in Seoul, have decreased since the implementation of the policies. Prevented hospital visits cases for asthma in the total population and younger population (0-18 years) were estimated as 500,000 (11.3% of hospital visit cases if there was no intervention) cases and 320,000 (15.5% of hospital visit cases if there was no intervention) cases, respectively in Seoul. Our study provides evidence for the possible beneficial effect of emission reduction policies on hospital visits for asthma.