Epidemiological studies indicate that NO2 may increase respiratory illness in older children (5–15 years). These findings are of concern because of the potential long-term effects. Studies indicate that repeated respiratory illness in older children (independent of NO2) is associated with increased lung damage in later life. Thus, any increases in such illnesses associated with NO2 could have subsequent, as well as immediate, consequences (WHO, 2000). The NO2 provisions of the ambient air NEPM are based on evidence that important health effects of NO2 occur above a threshold, and incorporate a safety factor accordingly (NEPC, 1998). Asthmatics are likely.