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Heal, Mathew R.; Kirby, Carolyn; Cape, J. N.

doi:10.1023/a:1006249016103

Cited by 27 publications

(27 citation statements)

References 13 publications

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“…For comparison, the median exposure-averaged analyser NO x /NO 2 ratio was 2.1 across all sites, and 2.2 and 2.0 for the Haymarket and Queen's Street sites, respectively. The data therefore provide further evidence of intrinsic over-read of NO 2 by PDT consistent with within-tube oxidation of a proportion of the NO also present at the exposure location, 10,11,16 and confirms the problem of using zero bias as a measure of accuracy.…”

Section: Discussionsupporting

confidence: 68%

“…In fact, an advantage of one week exposures is that the confounding effect of decreasing PDT NO 2 values with exposure duration, which may well be variable, should be minimised. 11 General linear modelling (GLM) in Minitab v.14 was used to test for significant factors acting on the two dependent variables %RSD and CAPTURE being investigated. The full GLM comprised: (a) the three factors 'Application Method', 'Solvent' and '%TEA' as the main-effect fixed factors under test; (b) the three pairwise combinations of these factors to test for significant interactions; (c) the two factors 'Analyst' and 'Exposure site' as additional main-effect random factors i.e.…”

Section: Methodsmentioning

confidence: 99%

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The effect of absorbent grid preparation method on precision and accuracy of ambient nitrogen dioxide measurements using Palmes passive diffusion tubes

Heal

2008

J. Environ. Monit.

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A few studies have suggested that the precision and accuracy of measurement of NO(2) by Palmes-type passive diffusion tube (PDT) are affected by the method of preparation of the triethanolamine (TEA) absorbent coating on the grids. Theses studies have been quite limited in extent and have tended to evaluate PDT accuracy as zero bias between PDT NO(2) value and the exposure-averaged NO(2) determined by co-located chemiluminescence analyser. This ignores the well-documented intrinsic systematic biases on PDT-derived NO(2), such as within-tube chemistry and exposure-duration nitrite loss, which may lead to non-zero bias values irrespective of effects of TEA absorbent preparation method on PDT accuracy. This paper reports on a statistical analysis of a large dataset comprising 680 duplicated PDT exposures spanning 146 separate exposure periods, spread over five urban exposure locations and a number of years. In each exposure period, PDTs prepared by between four and six different grid preparation methods were simultaneously compared. The preparation methods used combinations of the following: acetone or water as the TEA solvent; 20% or 50% as %TEA in the solution; and application of TEA solution by dipping grids for several minutes in the solution before drying and tube assembly, or by pipetting 50 microL of solution directly onto grids already placed in the PDT cap. These represent the range of preparation procedures typically used. Accuracy was evaluated as maximised nitrite capture within an exposure. Data were analysed by general linear modelling including examination of interaction between different aspects of grid preparation method. PDT precision and accuracy were both significantly better, on average, when the PDT grids were prepared by dipping in TEA solution, and neither solvent or %TEA used for the dipping solution were important. Where PDT preparation by pipetting TEA solution onto grids is to be used, better performance was obtained using 20% TEA in water. A systematic positive bias in PDT measure of NO(2), consistent with within-tube oxidation of NO to NO(2) and independent of preparation method, was again evident in this work.

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Section: Discussionsupporting

confidence: 68%

Section: Methodsmentioning

confidence: 99%

The effect of absorbent grid preparation method on precision and accuracy of ambient nitrogen dioxide measurements using Palmes passive diffusion tubes

Heal

2008

J. Environ. Monit.

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“…The authors attributed this to additional wind-induced positive bias at this site, supported by the observation that the co-located NO x PDT tubes (which will not be subject to within-tube chemical bias because the reaction converts between NO and NO 2 ) also had a positive bias of around 50%. Allowing for the possibility also of an exposure-duration-dependent negative bias over one-week of~8%, based on earlier work [47], the authors concluded that wind bias at this site could have been as high as 55-60%. They noted that these particular tubes were deployed in an exposed location, mounted at 3 m height without shelter on an air intake duct in the middle of a relatively open square, in one of the UK's windiest urban areas.…”

Section: Field Studiesmentioning

confidence: 94%

“…The model overestimations were subsequently compared against real PDT exposures at urban background sites in Edinburgh [46] and Cambridge [47], with average positive biases due to within-tube chemistry across all exposures at each location of 22% and 31%, respectively. The former study also showed that positive bias was lower for PDTs constructed of quartz glass, which transmit wavelengths for NO 2 photolysis, compared with standard acrylic PDTs.…”

mentioning

confidence: 99%

“…Evidence for an exposure-duration-associated negative bias in PDT determination of NO 2 is derived from co-located comparisons of concentrations derived from a single long-duration exposure (e.g., of four weeks, versus the average of consecutive co-located one-week or two-week exposures [46,47]) and from differences in these comparisons between summer and winter seasons. These studies very approximately estimate a "loss" rate for absorbed NO 2 − of a few percent (e.g., The study by Vardoulakis et al [25] for a year of monthly deployments in Birmingham (described in detail above) concluded from a comparison of four-and five-week exposures that photolysis, or other exposure-duration-dependent losses, at the absorbent was not a factor.…”

mentioning

confidence: 99%

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Biases in the Measurement of Ambient Nitrogen Dioxide (NO2) by Palmes Passive Diffusion Tube: A Review of Current Understanding

2019

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Palmes-type passive diffusion tubes (PDTs) are widely used to measure levels of nitrogen dioxide (NO2) in air quality studies. Molecules of NO2 diffuse down the concentration gradient established in the tube by their reactive conversion into nitrite (NO2−) with triethanolamine (TEA) absorbent at the inner end. The relatively low uptake rate for the tube geometry means that exposure-averaged NO2 concentration can be calculated from first principles using the diffusion coefficient, D, for NO2 in air. This review provides a critical assessment of the current understanding of sources and extent of potential bias in NO2 PDT measurements in each of the following methodological stages: preparation of the absorbent; quantification of the absorbed NO2−; deployment in the field; calculation of the exposure-average NO2 concentration from the absorbed NO2−; and assessment of PDT bias through comparison against a chemiluminescence NO2 analyser. The review has revealed strong evidence that PDT measurement of NO2 can be subject to bias from a number of sources. The most significant positive biases are ambient wind flow at the entrance of the tube potentially leading to bias of tens of percent, and within-tube chemical reaction between NO and O3 causing bias up to ~25% at urban background locations, but much less at roadside and rural locations. Sources of potentially significant negative bias are associated with deployment times of several weeks in warm and sunny conditions, and deployments in atmospheres with relative humidities <~75% which causes incomplete conversion of NO2 to NO2−. Evidence suggests that biases (positive or negative) can be introduced by individual laboratories in the PDT preparation and NO2− quantification steps. It is insufficiently acknowledged that the value of D is not accurately known—some controlled chamber experiments can be interpreted as indicating that the value of D currently used is too low, giving rise to a positive bias in PDT-derived NO2 concentration. More than one bias may be present in a given PDT deployment, and because the biases act independently the net effect on PDT NO2 determination is the linear sum of individual biases acting on that deployment. The effect of net bias can be reduced by application of a local “bias adjustment” factor derived from co-locations of PDTs with a chemiluminescence analyser. When this is carried out, the PDT is suitable as an indicative measure of NO2 for air quality assessments. However, it must be recognised that individual PDT deployments may be subject to unknown variation in the bias adjustment factor for that deployment.

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A miniaturized active sampler for the assessment of personal exposure to nitrogen dioxide

et al. 2005

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A personalized, miniaturized air sampling system was evaluated to estimate the daily exposure of pediatric asthmatics to nitrogen dioxide (NO2). The lightweight device (170 g) uses a sampling pump connected to a solid sorbent tube containing triethanolamine (TEA)-impregnated molecular sieve. The pump is powered by a 9 V battery and samples air over a 24 h period at a collection rate of 0.100 L/min. After exposure, the solid sorbent is removed from the tubes for spectrophotometric analysis (Griess Assay). The lower detection limit of the overall method for NO2 is 11 microg/m3. The linearity, precision and accuracy of the sampler was evaluated. Different NO2 concentrations generated in the laboratory (range: 50 to 340 microg/m3) were simultaneously measured by the TEA tube samplers and colocated continuous chemiluminescent NO(x) analyzers (reference method). The coefficient of determination for the laboratory test derived from ordinary linear regression (OLR) was r2 = 0.99 (y(OLR) = 0.94 x -4.58) and the precision 3.6%. Further, ambient NO2 concentrations in the field (range: 10-120 microg/m3) were verified with continuous chemiluminescent monitors next to the active samplers. Re-weighted least squares analysis (RLS) based on the least median squares procedure (LMS) resulted in a correlation of r2 = 0.68 for a field comparison in Riverside, CA (y(RLS) = 1.01 x -0.94) and r2 = 0.92 in Los Angeles, CA (y(RLS) = 1.31 x -7.12). The precision of the TEA tube devices was 7.4% (at 20-60 microg/m3 NO2) under outdoor conditions. Data show that the performance of this small active sampling system was satisfactory for measuring environmental concentrations of NO2 under laboratory and field conditions. It is useful for personal monitoring of NO2 in environmental epidemiology studies where daily measurements are desired.

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Untitled

Cited by 27 publications

References 13 publications

The effect of absorbent grid preparation method on precision and accuracy of ambient nitrogen dioxide measurements using Palmes passive diffusion tubes

The effect of absorbent grid preparation method on precision and accuracy of ambient nitrogen dioxide measurements using Palmes passive diffusion tubes

Biases in the Measurement of Ambient Nitrogen Dioxide (NO2) by Palmes Passive Diffusion Tube: A Review of Current Understanding

A miniaturized active sampler for the assessment of personal exposure to nitrogen dioxide

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