Decline of ambient air pollution levels due to measures to control automobile emissions and effects on the prevalence of respiratory and allergic disorders among children in Japan

In Japan, air pollution due to nitrogen oxides (NOx) and particulate matter (PM) has been gradually reduced since control measures based on the Automobile NOx/PM law were enforced beginning in 2001. The effects of decrease in air pollutants due to the control measures during the past decade on the prevalence of respiratory and allergic disorders such as asthma in children were evaluated. Using data of 618,973 children collected in 28 regions of Japan from 1997 to 2009, we evaluated whether reductions in the concentrations of nitrogen dioxide (NO2) and suspended particulate matter (SPM) contribute to the decrease in the prevalence of asthma, wheezing, bronchitis, allergic rhinitis, and atopic dermatitis by multiple linear regression analysis, including adjustments for related factors. The annual rates of decrease in air pollution in the PM-law-enforced areas were 2.0 and 2.5 times higher for NO2 and SPM, respectively, compared with those in the non-enforced areas. The prevalence of asthma decreased significantly at −0.073% per year in the areas in which measures based on the Automobile NOx/PM law were taken but not in area where such measures were not applied. Multiple linear regression analysis showed a reduction in the ambient air pollution was significantly associated with a reduction in the prevalence of asthma, with a rate of 0.118% [95% confidence interval (CI): 0.012–0.225] per 1ppb for NO2, and 0.050% [95% CI: 0.020–0.080] per 1μg/m3 for SPM. An increase in the ambient air pollution was associated with an increase in the prevalence of atopic dermatitis of 0.390% [95% CI: 0.107–0.673] per 1ppb for NO2, 0.141% [95% CI: 0.058–0.224] per 1μg/m3 for SPM. The changes in the prevalence of wheezing and allergic rhinitis were not significantly correlated with changes in air pollutant concentrations. The enforcement of measures to control automobile emissions based on the Automobile NOx/PM law was shown to have reduced air pollution and contributed to decreases in the prevalence of respiratory and allergic disorders in 3-year-old children. ●Measures to control automobile emissions improved the air quality in Japan.●We evaluated the effects of improved air quality on children׳s health.●The prevalence of asthma decreased in areas with lower levels of air pollution.●Enforcement of emissions controls may decrease the prevalence of asthma.