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Calibration of in situ analysers of air pollutants is usually done\udwith dry standards. In this paper, the influence of sample temperature and\udenvironmental humidity on benzene measurements by gas chromatography coupled\udwith a photoionisation detector (GC-PID) is studied. Two reference gas\udmixtures (40 and 5 µg m−3 nominal concentration\udbenzene in air) were subjected to two temperature cycles (20/5/20 °C and\ud20/35/20 °C) and measured with two identical GC-PIDs. The change in sample temperature did not produce any significant change in readings. Regarding ambient humidity, the chromatographs were calibrated for benzene with dry gases and subjected to measure reference standards with humidity (20 and 80 % at 20 °C). When measuring a concentration of 0.5 µg m−3\udbenzene in air, the levels of humidity tested did not produce any significant\udinterference in measurements taken with any of the analysers. However, when\udmeasuring a concentration of 40 µg m−3, biases in measurements of\ud18 and 21 % for each respective analyser were obtained when the\udrelative humidity of the sample was 80 % at 20 °C. Further\udtests were carried out to study the nature of this interference. Results show\udthat humidity interference depends on both the amount fractions of water\udvapour and benzene. If benzene concentrations in an area are close to its\udannual limit value (5 µg m−3), biases of 2.2 % can be expected\udwhen the absolute humidity is 8.6 g cm−3 – corresponding to a relative humidity of 50 % at 20 °C. This can be accounted for in\udthe uncertainty budget of measurements with no need for corrections. If\udbenzene concentrations are above the annual limit value, biases become\udhigher. Thus, in these cases, actions should be taken to reduce the humidity\udinterference, as an underestimation of benzene concentrations may cause a\udmismanagement of air quality in these situations

Influence of sample temperature and environmental humidity on measurements of benzene in ambient air by transportable GC-PID