Do pressure changes have an influence on ambient air chemiluminescence NOx measurements?

Ferradás

2012

J. Environ. Monit.

Self Cite

According to Directive 2008/50/EC, all equipment used for NO(x) fixed measurements must comply with the reference method or equivalent by 11 June 2013. Up to that date, non-type-approved equipment can continue to be used in air monitoring networks and will probably also be used in air pollution studies even after that date. In this context, it is advisable to know how these "old" measuring instruments respond to the requirements of European Standard EN 14211: 2005: Ambient Air Quality--Standard method for the measurement of the concentration of nitrogen dioxide and nitrogen monoxide by chemiluminescence. In this work, we carry out a thorough performance evaluation of two commercial NO(x) analysers, both purchased before 2010, according to the mentioned Standard. Results show that water vapour interference is one of the most important disconformities with this Standard. The expanded uncertainty estimation of both analysers was below the quality objective of the above-mentioned Directive (15%); however, this calculation was performed by applying some modifications to the proposed model of Standard EN 14211. These modifications are also discussed in the paper.

Section: Resultsmentioning

confidence: 99%

Performance evaluation of two commercial chemiluminescence NO_xanalysers according to European Standard EN 14211

Ferradás

2012

J. Environ. Monit.

Self Cite

“…Whereas in the literature, we can find great many works about interference species in air quality processes of quantifying regulated gas pollutants by means of standardised techniques (Spicer et al 2010;Wilson and Birks 2006;Williams et al 2006;Dunlea et al 2006;Leston et al 2005;Holloway et al 2000;Luke, 1997;Fried et al 1991), there are very few works studying instrument reading deviations due to changes in sampling and monitoring conditions. In this sense, we should mention the recent work on chemiluminescence NO x analyzers by Doval Miñarro et al (2011a), which studied the deviations in readings that take place when changes in atmospheric or sample pressure occur. The conclusions of the said work were that differences in measurements were practically negligible for fixed analyzers subjected to usual changes in atmospheric pressure (<±5 kPa); however, deviations could be as high as 7% if ±10 kPa pressure changes took place in the inlet sample line for causes different from ambient pressure changes, e.g.…”

mentioning

confidence: 97%

Influence of temperature changes on ambient air NOx chemiluminescence measurements

Ferradás

Martínez

2011

Environ Monit Assess

Self Cite

Users of automatic air pollution monitors are largely unaware of how certain parameters, like temperature, can affect readings. The present work examines the influence of temperature changes on chemiluminescence NO(x) measurements made with a Thermo Scientific 42i analyzer, a model widely used in air monitoring networks and air pollution studies. These changes are grouped into two categories according to European Standard EN 14211: (1) changes in the air surrounding the analyzers and (2) changes in the sampled air. First, the sensitivity tests described in Standard EN 14211 were performed to determine whether the analyzer performance was adapted to the requirements of the standard. The analyzer met the performance criteria of both tests; however, some differences were detected in readings with temperature changes even though the temperature compensator was on. Sample temperature changes were studied more deeply as they were the most critical (they cannot be controlled and differences of several tens of degrees can be present in a single day). Significant differences in readings were obtained when changing sample temperature; however, maximum deviations were around 3% for temperature ranges of 15°C. If other possible uncertainty contributions are controlled and temperature variations with respect to the calibration temperature are not higher than 15°C, the effect of temperature changes could be acceptable and no data correction should have to be applied.

Study of the effect of sample pressure on in situ BTEX chromatographs

Trigueros

Duperón

et al. 2016

Environ Monit Assess

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/m) 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/m) 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.