P Petrochina, in the production process to obtain oil raw materials, established the Mudi Central Processing Area (CPA) Unit, Tuban, East Java. In the processing process, emission of exhaust gases is discharged through the gas combustion process in the Flare unit. Flare is a combustion flare for the safe disposal of hydrocarbon fumes that are shaped like a torch, whose function is to burn the exhaust gases produced from each oil production process before being discharged into the atmosphere. The combustion is carried out to decompose the gases into gases that are not too dangerous in a certain concentration. This evaluation study discusses the air quality around the CPA area, whether the area is exposed to H2O, SO2 and NO2 gases as a result of exhaust gas emissions in the Petrochina CPA Mudi Flare.Approaches are made to the measurement results with theoretical calculations. The theoretical approach is carried out using mathematical modeling, namely the Gaussian Spread Model. By using this Gaussian Spread Model, it is hoped that it can predict the concentrations of H2S, SO2 and NO2 in ambient air in a location around a pollutant source (flare). The use of the Gaussian dispersion model is also supported by the use of formulas such as the Slade formula (1968) for calculating wind velocity over the chimney and determining the air stability class with the Holland formula (1953) to determine the burst height and effective height of the chimney. The wind speed factor affects the results of the Gaussian spread calculation.Based on the results of measurements and theoretical calculations in the discussion chapter, it shows that the concentration of the three parameters is still below the Ambient Air Quality Standard (SK. Gub. Jawa Timur No. 192/996), which is 42 ug / Nm3 for H2S, the comparison of the measurement results with theoretical lines has a large degree of deviation, it is possible to allow flowrate, combustion temperature and unstable wind conditions at the time of measurement. In addition, the H2S concentration fluctuates from the CPA unit.The farthest distribution pattern is the Southwest down wind, where the average wind speed is the lowest when compared to other downwinds, causing the radius of its distribution to be the farthest in its range, with a maximum H2S concentration of 0.0249-0.0420 ug / Nm3, the maximum SO2 concentration is 5.2137 -7.8942 ug / Nm3, and the maximum NO2 concentration is 0.0057-0.0101 ug / Nm3.