In our study, Children in all three districts were exposed to fairly high levels of air pollution. The 5-year annual mean concentration of NO2 in the three study districts exceeded the Chinese NAAQS. The concentrations of all pollutants, even in LPD, far exceeded the 2005 WHO Air Quality Guidelines, which recommended much more stringent standards than those of the NAAQS. 26 Within the highlypolluted environment, we still observed a significant difference in lung growth among children exposed to different levels of air pollutants within a rather short period
(only 6 month). We postulate that the absolute difference
in lung functions could have been due to a cumulative
effect of long-term exposure of the children to air
pollution.