Previous studies reported inconsistent findings for the
associations of traffic-related air pollution with asthma
symptoms and doctor diagnosed asthma [6,7]. Associations
of NO2 and PM2.5 with overall wheezing until the age of
8 years were observed in another study in the Netherlands
[14]. A Swedish cohort study observed associations of air
pollution in the first year of life with persistent wheezing
until 4 years of age [25]. A study in Germany observed no
associations of long term exposure to PM2.5 or NO2 with
the risks of parental reports of asthma symptoms, but