- For potential subjects satisfying these inclusion criteria, a passive NO2 monitor will be sent to the home for placement in the main living space for one week. Families will be called after one week and instructed to cap and return the NO2 monitor in a pre-paid mailer. Families of children living in homes where the one-week integrated average NO2 concentration is ≥ 15 ppb will be invited to participate. We will permit the enrollment of more than one eligible child per family.