Respiratory health associated with exposure to automobile exhaust. II. Personal NO2 exposure levels according to distance from the roadside.

We have conducted several studies to investigate the effect of automobile exhaust on respiratory symptoms. This study was designed to explore differences in personal exposure levels among residents of zones located varying distances from trunk roads with heavy traffic in Tokyo. Personal nitrogen dioxide (NO2) concentration levels for residents and NO2 concentrations inside and outside the residences of each study participant were measured during ten seasons over three years. Three residential zones were determined as follows: Zone A was 0-20 m from the roadside; Zone B was 20-150 m; and Zone C, a reference zone, was a residential district in a suburban area. Approximately fifty residents were selected as the subjects of NO2 measurements. Study participants were female, between 40 and 60 years of age, and nonsmokers. All participants used gas cooking stoves with electric ignition. Outdoor NO2 concentrations in Zone A were always the greatest among the three zones during the study periods, and those in Zone C were consistently the lowest. Personal exposure levels in Zone A were generally higher than those in the other zones, and concentrations in Zone C were the lowest during seasons when no indoor heating was used. The highest mean values for personal exposure levels in Zones A, B, and C were 63.4, 61.0, and 55.3 ppb, respectively. In analyses in which participants were stratified by heater type, the mean personal exposure levels in Zone A were the highest and the levels in Zone C were the lowest for participants without unvented heaters; differences of NO2 levels between Zones A and C ranged from 10.0 to 23.9 ppb. When there were no indoor NO2 sources except gas cooking stoves, both indoor and personal levels of NO2 were attributable primarily to motor vehicle exhaust. In contrast, the use of unvented heaters during the heating seasons could cause NO2 exposures comparable to those attributable to motor vehicles.