Sources and Concentrations of Indoor Nitrogen Dioxide in Barcelona, Spain

Sources and concentrations of indoor nitrogen dioxide (NO 2 ) were examined in Barcelona, Spain, during 1996 -1999.A total of 340 dwellings of infants participating in a hospital-based cohort study were selected from different areas of the city.Passive filter badges were used for indoor NO 2 measurement over 7-30 days.Dwelling inhabitants completed a questionnaire on housing characteristics and smoking habits.Data on outdoor NO 2 concentrations were available for the entire period of the study in the areas of the city where indoor concentrations were determined.Bivariate analysis was performed to investigate relationships between indoor NO 2 concentrations on one hand and outdoor NO 2 concentrations, housing, and occupant characteristics on the other.Stepwise multiple linear regression was performed with variables that were found to have a significant bivariate relationship.Indoor NO 2 mean values ranged between 23.57ppb in 1996 and 27.02 ppb in 1999, with the highest yearly value of 27.82 ppb in 1997.In the same time period, mean outdoor NO 2 concentration ranged between 25.26 and 25.78 ppb with a peak of 30.5 ppb in 1998.Multiple regression analysis showed that principal sources of indoor NO 2 concentrations were the use of a gas cooker, the absence of an extractor fan when cooking, and cigarette smoking.The absence of central heating was also associated with higher NO 2 concentrations.Finally, each ppb increase in outdoor NO 2 was associated with a 1% increase in indoor concentrations. IMPLICATIONSIndoor NO 2 was measured in Barcelona and related to housing characteristics, smoking habits, and outdoor NO 2 concentrations in different areas of the city.Indoor NO 2 concentrations were quite high, and principal determinants were the energy sources, cigarette smoking, ventilation, and dampness.Contradictory results exist regarding the relation between increase of respiratory disease and exposure to NO 2 .Values of indoor NO 2 in Barcelona are needed to verify an eventual relation between indoor NO 2 and respiratory symptoms found by the Asthma Multicenter Infant Cohort Study, aimed at assessing the effects of environmental exposures in the inception of atopy and asthma.