Beginning in October of 1996, indoor and sometimes outdoor air at an occupied house in a suburban area of Virginia has been monitored continuously for partricles, PAH, and CO. This ongoing study is aimed at providing a record of real-time particle fluctuations over an extended period (1-2 years) in an occupied townhouse. In general, ordinary daily activities provide the experimental framework, although occasionally special experiments are done to investigate phenomena of interest. The main goals of the study are to: (1) Identify and characterize major sources of particles, both indoor and outdoor. If possible, determine the fraction of the indoor concentration due to each type of source; (2) Measure particle deposition rates for ultrafine, fine, and coarse particles, varying from 0.01 to > 10 micrometers; and (3) Measure PAH and black carbon in conjunction with other parameters of interest, including CO, temperature, relative humidity, and CO2.