A randomized, double-blind, crossover intervention study of traffic-related air pollution and airway inflammation in healthy adults

BACKGROUND: Traffic-related air pollution (TRAP) may increase the risk of respiratory disease. The components of TRAP that are responsible for its respiratory toxicity are largely unknown. The objective was to identify the component(s) of TRAP that cause airways inflammation using fractional exhaled nitric oxide (FE(NO)) and randomized interventions. METHODS: A randomized, double-blind, crossover intervention study was conducted in which 39 healthy university students spent 2 hours next to a busy road. During exposure, participants wore either a powered air-purifying respirator (PAPR) or an N95 facemask. PAPRs were fitted with a fine particle (PM(2.5)) filter, a PM(2.5) and volatile organic carbon (VOC) filter, or a sham filter, and were blinded to filter type. The four interventions (three PAPR filters and N95) were assigned randomly for each participant and separated by at least 1 week. FE(NO) was measured before and immediately after each roadside exposure, and at 1, 2, 4, and 6 hours after exposure. RESULTS: With the sham PAPR filter, the mean postexposure FE(NO) increased an average of 2.3 ppb (±4.4) compared with the pre-exposure level. Similar increases in FE(NO) were seen with both the PM(2.5) PAPR filter and the N95 mask, but no increase was seen with the combination PM(2.5) and VOC PAPR filter. CONCLUSIONS: Because PAPR filters do not filter inorganic gases (e.g., NO(2) or carbon monoxide), it is concluded that the VOC component of TRAP rather than either the particulate matter or the inorganic gases component is responsible for the airway inflammation caused by TRAP exposure.