Background Petrochemical workers are exposed to a variety of airborne toxic compounds which have been associated with increased risk for respiratory outcomes. However, long-term exposure to SO2, NO2, O3, H2S and NH3 in relation to spirometric parameters and self-reported respiratory problems is largely unknown. Methods Airborne concentration levels of SO2, NO2, O3, H2S and NH3 were collected from two fixed stations over a 3-year period in a petrochemical complex. We assessed spirometric parameters and respiratory symptoms in the petrochemical workers (n = 200) and in an unexposed group (n = 200). We calculated β-coefficients (β) and odds ratios (ORs) with 95% confidence intervals (CIs) before and after adjustment for covariates. Results The mean airborne pollution levels were 159 µg/m3 for SO2, 43 µg/m3 for NO2, 66 µg/m3 for O3, 6 µg/m3 for H2S, and 24 µg/m3 for NH3. We found a significant reduction in spirometric parameters among petrochemical workers compared to the unexposed: FEV1 (forced expiratory volume in 1s) (adjusted β -12; 95%CI -16, -7.64), FEV1/ FVC (forced vital capacity) (β -7.26; 95%CI -9.23, -5.28), and PEF (peak expiratory flow) (β -6.61; 95%CI -12, -0.76). Additionally, we observed higher adjusted risks for any respiratory symptom (OR 4.69; 95%CI 1.76, 12), mucus (OR 4.36; 95%CI 1.70, 11) and shortness of breath (OR 15; 4.95, 46) among petrochemical workers compared to the unexposed group. Conclusions Most measured airborne pollution levels were within the ambient recommendation levels. Still, long-term exposure to low level airborne pollutants, reduced FEV1, FEV1/FVC and PEF, and increased respiratory symptoms in Iranian petrochemical workers compared to unexposed controls.