글의 내용과 일치하는 것은? A new study reports that the cleaner air has been accompanied by a significant decrease in childhood lung problems. The study used data on ozone, nitrogen dioxide and particulate matter for each year. Parents also provided regular updates about symptoms like coughing and phlegm production in their children. Among children with asthma, air-pollution reduction was consistently associated with reductions in respiratory symptoms. For example, in children with asthma, reductions in fine particulate matter were associated with a 32-percent reduction in symptoms, while lower levels of ozone were linked to a 21-percent reduction. The associations were weaker, but still significant, in children without asthma. “Clearly, the reduction in air pollution levels have translated into improvements in respiratory health,” said Kiros Berhane, a professor of preventive medicine at the University of Southern California. “Especially for parents of children with asthma, this is very good news, but we see significant improvement in children without asthma as well.”