An analysis of factors that influence personal exposure to nitrogen oxides in residents of Richmond, Virginia

Nitrogen oxides (NOx) are ubiquitous pollutants in outdoor and indoor air. However, epidemiologic studies that evaluate health effects associated with NOx commonly rely upon outdoor concentrations of NOx, nitrogen dioxide (NO2), or residence characteristics as surrogates for personal exposure. In this study, personal exposures (48 h) and corresponding indoor and outdoor concentrations of nitric oxide (NO), NO2, and NOx were measured (July- September) in 39 adults and 9 children from 23 households in Richmond, Virginia, using Ogawa passive NOx monitors. Demographic, time-activity patterns, and household data were collected by questionnaire and used to develop exposure prediction models. Adults had higher NO2, NO, and NO, exposures (means: 16, 63, and 79 ppb, respectively) than children ( 13, 49, and 62 ppb). Measurements taken in bedrooms ( 18, 57, and 75 ppb) and living rooms ( 19, 65, and 84 ppb) surpassed measurements taken outdoors ( 15, 21, and 36 ppb). In indoor locations, NO, concentrations were influenced largely by NOx and consequently, personal exposure prediction models for NOx were reflective of models for NO. Statistical models that best predicted personal exposures included indoor measurements; outdoor measurements contributed relatively little to personal exposure. Close to 70% of the variation in personal NO2 and NOx, exposure was explained by two variable models (bedroom NO2 and time spent in other indoor locations; bedroom NOx and time spent in kitchen). Given appropriate resources, measurement error in epidemiologic studies can be reduced significantly with the use of personal exposure measurements or prediction models developed from indoor measurements and survey data.