A differential optical absorption spectrometer (DOAS) has been in operation since August 1991 at the U.S. EPA in RTP, NC. The analyzer unit is located in an environmentally-controlled shelter in the EPA parking lot. Four separate open optical paths have been established, ranging from 202 to 816 meters in length. The longest path crosses a highway while all the shorter paths are located near parking lots. Semi-continuous measurements of SO2, O3, NO, and NO2 were made. The measurement cycle involves measurements on each path in sequence. The total of all measurements on all paths requires approximately 20 minutes to complete, thus there are three values for each unique gas-path combination per hour. The instruments were measuring the same gases. Their results are also reported as hourly averages. Comparison of the long-path DOAS measurements with the FRM point measurements indicates a high level of correlation. Considering the potential problem of comparing a long-path measurement to a point measurement, the high correlation is encouraging. The shorter DOAS paths yielded the highest correlations with the point measurements, as expected.