An OPSIS differential optical absorption spectrometer (UV-DOAS) open path demonstration system was operated over a 7 week period at an urban air monitoring site in East Hartford, CT. The study purpose was primarily to compare acetaldehyde and formaldehyde from the OPSIS to extractive data gathered by use of coated cartridges under an EPA recognized method at the same site. A secondary goal was to compare benzene, toluene, NO2, and O3 OPSIS open path data to data gathered by methods currently approved or recognized by the EPA. This was the first field test for acetaldehyde, and the study showed that OPSIS was not able to detect ambient acetaldehyde concentrations. However, the system was able to measure ambient levels of the other 5 pollutant parameters. The correlation of OPSIS data was excellent for O3 and NO2 and less well correlated for formaldehyde, benzene and toluene. The paper describes the monitoring equipment operational characteristics, equipment deployment, and calibration, and data comparison results. A brief summary is given on suggested improvements and retesting requirements.