Atmospheric filter samples were collected during several field campaigns in 1998/1999 from two locations in and around the greater Toronto area. The objective of the campaigns was to investigate the difference in composition of the organic fraction of atmospheric aerosols at both an urban and rural site for different seasons. The composition of organic particulate matter, with an interest in organic carbon, elemental carbon, alkanoic acids, n-alkanes, and polycyclic aromatic hydrocarbons (PAHs), was investigated using thermal desorption, solvent extraction, derivatization, and analysis by gas chromatography/mass spectroscopy. The concentrations measured were similar to other observations in urban and rural areas with seasonal differences observed at both sites. PM2.5 levels were larger in February at both urban and rural sites due to weather conditions favorable for buildup of particles. Organic carbon/elemental carbon ratios were typical of emission values except for the rural site where a greater potential for biogenic-related particles, as well as secondary production, likely played a role. A comparison of the chemical species to the total organic carbon revealed that the acids, alkanes, and PAHs account for a very small portion of the mass, demonstrating the need for further analytical developments. Preliminary results of the tracer analyses indicated that at the urban site the distribution of alkanoic acids atmospheric concentrations was correlated to diesel emissions. The n-alkanes distribution profile was representative of both anthropogenic sources for the urban site and biogenic sources for the rural site. At the rural site one sample exhibited a local source of atmospheric aerosol derived from vegetation.