Nitrogen dioxide and particulates apparently were the greatest culprits, although high ozone exposure played a significant role in girls with asthma. Boys' breathing capacity was affected by high ozone exposure too, but only in those who spent a lot of time outdoors. Boys tended to be more affected by respiratory illnesses. In their case, wheezing was linked to nitrogen dioxide and acid vapor. But researchers noted that although boys initially suffered more from asthma, girls essentially caught up with them in that regard by the time they reached high school.
Researchers hope to tease out the reasons for the gender differences as the study progresses.
Possible explanations include variations in boys' and girls' lung volume and airflow, growth rates and hormonal effects. There were other findings that stumped researchers. For example, they could not explain why the incidence of excessive respiratory disease did not correlate with the highest levels of outdoor air pollution. This contrasts with the separate finding of girls' reduced lung capacity in highly polluted areas. Whatever the answer, the investigators say the findings underline the importance of indoor pollutants such as mildew and cigarette smoke.