Browsing by Subject "Air monitoring"

Now showing 1 - 2 of 2
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    Do pressure changes have an influence on ambient air chemiluminescence NOx measurements?
    (Elsevier, 2011-09) Doval Miñarro, Marta; González Ferradás, Enrique; Romero Trigueros, Cristina; Barberá Rico, Jonathan; Ingeniería Química
    Users of automatic air pollution monitors are largely unaware of how certain parameters, like pressure, can affect readings. The present work examines the influence of inlet pressure changes on chemiluminescence NOx measurements. These changes have been grouped into two categories: (i) those due to changes in atmospheric pressure and (ii) those produced by any other reason (e.g., clogs in the inlet sampling line). Atmospheric pressure changes were simulated varying both the inlet and the outlet sample line pressures in the same way, whereas sample pressure changes were produced modifying only the inlet sample line pressure. Analyzer calibration was performed with zero air and 200 nmol mol−1 of NO at 101.3 kPa. The test pressures ranged from −10 to +10 kPa with respect to the calibration pressure. ANOVA and Dunnett's tests were performed to look for significant differences between measurements obtained under calibration conditions and those obtained under different pressure conditions. The differences in measurements were practically negligible for fixed analyzers subjected to usual changes in atmospheric pressure (<±5 kPa); however, differences could be as high as 7% if ±10 kPa pressure changes took place in the inlet sample line for causes included in the second group.
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    Open Access
    Study of the effect of sample pressure on in situ BTEX chromatographs
    (Springer, 2016-11-12) Romero Trigueros, Cristina; Doval Miñarro, Marta; González Duperón, Esther; Marzal Martínez, Francisco José; González Ferradás, Enrique; Ingeniería Química
    In this paper, the influence of sample pressure on benzene measurements obtained with two automated in situ gas chromatographs is studied. The analysers were calibrated using a non-linear regression at 293 ± 1 K and 101.3 ± 0.2 kPa. A gas mixture of benzene in air (5 μg/m3) was produced and measured at calibration conditions. Subsequently, the sample pressure was changed to 80 and 110 kPa. Differences in readings were observed even though the pressure compensators were on, indicating incorrect performance of this tool. Further tests with two different benzene in air mixtures (5 and 40 μg/m3) at 80, 90, 105 and 110 kPa were also carried out. Results showed that the analysers take air from one or several unidentified inlets (apart from the sampling port) when the sampling pressure is lower than the atmospheric one. This is usually the case in air monitoring stations, so this phenomenon is particularly important as systematic biases could be affecting air quality data.