A model for estimating indoor concentrations of acid aerosol was applied to data collected during the summer of 1989, in a densely populated location in New Jersey. The model, from a study of a semi-rural community in Pennsylvania, was used to estimate indoor concentrations of aerosol strong acidity (H+) at an elderly care residence in suburban New Jersey. The purpose of the present work is to assess the applicability of the model for predicting H+ exposures in a suburban environment and to evaluate the models performance for daytime and nighttime periods. Indoor and outdoor samples were taken at an elderly care home between June 20 and July 30, 1989. The indoor and outdoor monitoring schedule collected two 12-h samples per day. Samples were taken with the Indoor Denuder Sampler (IDS). Samples were analyzed for indoor and outdoor concentrations of aerosol strong acidity (H+), ammonia (NH3), and anion determination. The model generally underestimated the indoor H+ concentration. Slight improvement was seen in the model estimate of H+ for the nighttime period (7:00 pm to 7:00 am, local time). The model applied to the site in New Jersey did not predict the indoor H+ concentrations as well as it did for the experiment from which it was developed.