Concentrations and determinants of outdoor, indoor and personal nitrogen dioxide in pregnant women from two Spanish birth cohorts

Abstract

Determinants of outdoor, indoor and personal concentrations of nitrogen dioxide (NO 2) were assessed in a subset of pregnant women of the Spanish INMA (Environment and Childhood) Study. Home indoor and outdoor NO 2 concentrations were measured during 48 h with passive samplers for 50 and 58 women from the INMA cohorts of Valencia and Sabadell, respectively. Women from Sabadell also carried personal NO 2 samplers during the same period. Data on time–activity patterns, socio-economic characteristics, and environmental exposures were obtained through questionnaires. Multiple linear regression models were developed to predict NO 2 levels. In Valencia, median outdoor NO 2 levels (42 µg/m 3) were higher than median indoor levels (36 µg/m 3). In Sabadell, personal NO 2 showed the highest median levels (40 µg/m 3), followed by indoor (32 µg/m 3) and outdoor (29 µg/m 3) levels. Personal exposure to NO 2 correlated best with the indoor NO 2 levels. Temporal and traffic-related variables were significant predictors for outdoor NO 2 levels. Thirty-two percent of the indoor NO 2 variability in the two cohorts was explained by outdoor NO 2 levels and the use of the gas appliances. The model for personal exposure accounted for 59% of the variance in NO 2 levels in Sabadell with four predictor variables (outdoor and indoor NO 2 levels, time spent in outdoor environments and time exposed to a gas cooker). No significant association was found between personal or indoor NO 2 levels and exposure to environmental tobacco smoke (ETS) at home. Personal NO 2 levels were found to be strongly influenced by indoor NO 2 concentrations. The study supports the use of time–activity patterns along with indoor measurements to predict personal exposure to traffic-related air pollution.