THE RELATIONSHIP BETWEEN AIRBORNE ACIDITY AND AMMONIA IN INDOOR ENVIRONMENTS

Indoor acid aerosol, nitric acid (HNO3), and ammonia (NH3) concentrati ons were measured in 47 homes in State College, Pennsylvania, during t he summer of 1991. From each home, 12-hour indoor, 12- and 24-hour out door, and 12-hour air exchange samples were collected continuously ove r a 5-day period. Additionally, questionnaires were administered daily by field technicians to obtain information on house occupant number, ventilation, gas stove use, pets, and other housing characteristics. I n this paper, we discuss the relationship between NH3 and correspondin g concentrations of aerosol strong acidity (H+) and HNO3 inside these homes. As part of this analysis, we also examined indoor/outdoor conce ntration relationships and identified housing factors that may influen ce indoor levels. In State College, indoor NH3 concentrations were hig her than corresponding outdoor levels, with air conditioner use, air e xchange rates, and occupant number identified as important determinant s of indoor levels. Indoor concentrations of both H+ and HNO3 were sub stantially lower than outdoor levels, as homes with air exchange rates less than one exchange per hour were found to have essentially no aci d indoors. These low H+ and HNO3 levels likely resulted from their rea ction with indoor NH3 and with indoor surfaces. Indoor NH3 concentrati ons were higher than outdoor levels, indicating the presence of indoor NH3 sources; however, correlations between indoor NH3 and both pets a nd occupants, its primary indoor sources, were weak and negative, resp ectively. Mass balance models that included an NH3 neutralization term were found to predict indoor H+ concentrations reasonably well, repre senting a substantial improvement oyer outdoor concentrations alone. T he accumulation of NH3 indoors was found to be the primary determinant of indoor H+ and HNO3 levels.