Influence of sample temperature and environmental humidity on measurements of benzene in ambient air by transportable GC-PID
| Autor: | Cristina Romero-Trigueros, Enrique González Ferradás, Marta Doval Miñarro, Esther González Duperón |
|---|---|
| Jazyk: | angličtina |
| Rok vydání: | 2017 |
| Předmět: |
Atmospheric Science
010504 meteorology & atmospheric sciences Chemistry lcsh:TA715-787 lcsh:Earthwork. Foundations Analytical chemistry Humidity 010501 environmental sciences 01 natural sciences lcsh:Environmental engineering Apparent temperature chemistry.chemical_compound Environmental chemistry Calibration Relative humidity Gas chromatography lcsh:TA170-171 Benzene Air quality index Water vapor 0105 earth and related environmental sciences |
| Zdroj: | Atmospheric Measurement Techniques, Vol 10, Pp 4013-4022 (2017) |
| ISSN: | 1867-8548 1867-1381 |
| Popis: | Calibration of in situ analysers of air pollutants is usually done with dry standards. In this paper, the influence of sample temperature and environmental humidity on benzene measurements by gas chromatography coupled with a photoionisation detector (GC-PID) is studied. Two reference gas mixtures (40 and 5 µg m−3 nominal concentration benzene in air) were subjected to two temperature cycles (20/5/20 °C and 20/35/20 °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 benzene in air, the levels of humidity tested did not produce any significant interference in measurements taken with any of the analysers. However, when measuring a concentration of 40 µg m−3, biases in measurements of 18 and 21 % for each respective analyser were obtained when the relative humidity of the sample was 80 % at 20 °C. Further tests were carried out to study the nature of this interference. Results show that humidity interference depends on both the amount fractions of water vapour and benzene. If benzene concentrations in an area are close to its annual limit value (5 µg m−3), biases of 2.2 % can be expected when 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 the uncertainty budget of measurements with no need for corrections. If benzene concentrations are above the annual limit value, biases become higher. Thus, in these cases, actions should be taken to reduce the humidity interference, as an underestimation of benzene concentrations may cause a mismanagement of air quality in these situations. |
| Databáze: | OpenAIRE |
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