The Rice University Fine Particulate Matter Air Sampling Study (1999--2000) identified and quantified the fine particulate matter (PM2.5) in an urban setting in Houston, Texas. The study lasted over two time periods to characterize the seasonal changes; the summer period was between August 16, 1999 and October 1, 1999 and the winter period was between December 18, 1999 and January 31, 2000. PM2.5 was isolated with a cyclone separator and quantified through gravimetric analysis. The major gaseous species (SO 2, gaseous NO3, NH3) and chemical species (organic carbon, elemental carbon, SO42--, NO3 --, NH4+, Na +, K+, and Cl--) were collected by multiple types of filter media and analyzed by ion chromatography, gas chromatography, mass spectrometry, and thermal/optical carbon analysis. PM 2.5 concentration during the summer and winter periods was 8.2 +/- 0.6mug/m3 and 6.2 +/- 0.6mug/m3 respectively and did not exceed the NAAQS PM2.5 standard. The major particulate species (in terms of mass fractions in the summer/winter) were OC (39%/36%), SO4 (20%/9%), NH4 (8%/4%), EC (3%/3%), and NO3 (1%/7%). In both time periods, a large mass fraction was attributed to unknown materials (28%/38%). The OC, SO4, and NH4 mass fraction decreased from the summer to the winter while the NO3 and EC mass fraction increased. The organic fraction of the particulate matter contained n-alkanes and polycyclic aromatic hydrocarbons.