Influence of environmental parameters on the accuracy of nitrogen dioxide passive diffusion tubes for ambient measurement

Abstract

Two studies at three sites in the UK provided confirmation that systematic positive bias in NO2 diffusion tube measurement occurred because of changes to "within-tube" chemistry, rather than eddy diffusion at the mouth of the tube. In the first study in Cambridge, UK, sampler overestimation for 1 and 2 week exposures was compared to corresponding time-averaged monitor measurements (NO-NO2-NOx, O3) and weather variables. Noninearity between sampler and monitor NO2 measurements was interpreted in terms of spatial and temporal variations in relative and absolute availability of NO, NO2 and O3 at the site. A maximum overestimation occurred for an exposure mean NO2/NOx approximately 0.5. The separate contributions of reduced NO2 photolysis and eddy diffusion were compared in Study II using samplers of two materials, acrylic and quartz, and of different lengths (40, 55, 71 and 120 mm) at three sites: Norwich background, Cambridge intermediate, London kerbside. For compared sites, NO2 measured by acrylic samplers was significantly higher than for equivalent quartz samplers. For quartz samplers [NO2]mean was only just above the monitor at Norwich and London; sampler/monitor NO2 = 1.04 (P = 0.59) and 1.01(P = 0.76), respectively. For acrylic samplers the order of [NO2]mean was 40 mm > 120 mm > 71 mm > or = 55 mm. Excepting 40 mm samplers, this accords with a chemical bias where co-diffusing NO and 03 molecules in longer tubes have more time to react to form excess NO2. Bias in 40 mm samplers is discussed. Eddy diffusion is negligible for standard samplers because [NO2]mean was equivalent for 55 mm and 71 mm acrylic samplers and close to monitor NO2 for 71 mm quartz tubes. Both studies showed that sampler accuracy was dependent on location. Significantly, overestimation was greatest (approximately 3-4 ppb) where the NO2 annual mean was approximately 20 ppb, close to the UK and EU air quality standard of 21 ppb.

The Use of Passive Diffusion Tubes for Measuring Concentrations of Nitrogen Dioxide in Air

“…Atkins et al (17) saw no effect of wind speed in the range 1.0 to 4.5 m/s for 1 week exposure of Palmes tubes. A similar lack of correlation with wind speed has been reported by other authors for outdoor samplers (21,30), although unsheltered diffusion tubes have shown larger (up to 18%) apparent sampling rates than adjacent sheltered tubes (32,33), which may be an effect of wind speed or turbulence. Similar lower sampling rates in sheltered tubes compared with adjacent unsheltered tubes have been noted in other studies (27).…”

“…In their modelling of the situation, the authors took no account of chemical reactions inside the tube during sampling, which may have affected the apparent sampling rates outdoors. More recent experiments outdoors with tubes of different lengths and of different materials (acrylic vs. quartz) (21) showed no effect of diffusion length for quartz samplers at 120 or 71 mm, implying no effect of wind shortening, although enhanced sampling attributed to wind shortening was observed for the shortest diffusion length (40 mm). The difference between the different tube materials was dependent on tube length.…”

Field performance evaluation of Maxxam passive samplers for regional monitoring of ambient SO2, NO2 and O3 concentrations in Alberta, Canada

“…Pollutant uptake by passive samplers can be affected by meteorological conditions, such as temperature, relative humidity, and air movement at the surface (Tang et al, 1997(Tang et al, , 1999Tang and Lau, 2000;Krupa and Legge, 2000;Tang, 2001;Kirby et al, 2001;Partyka et al, 2007;Fraczek et al, 2009;Salem et al, 2009;Zabiegala et al, 2010), as well as radiation (Krupa and Legge, 2000). Seasonality can also influence the performance of passive samplers (Logan, 1985;Legge and Krupa, 1990;Tang et al, 1997;Krupa and Legge, 2000).…”

Field Study of Diffusion Collection Rate Coefficients of a No2 Passive Sampler in a Mediterranean Coastal Area

“…The passive diffusion tube has been used for many years to measure outdoor concentrations of NO 2 across rural (Atkins and Lee, 1995) and urban (Campbell et al, 1994) national networks, and for more local scale concentration variations (Reeuwijk et al, 1998;Kirby et al, 2001). The increased emphasis on NO 2 as an air pollutant is partly a result of the fact that concentrations of NO 2 in urban areas have not declined in recent years, and the current requirement for some local authorities to review air quality in their areas makes it likely that the use of passive samplers will increase for compliance with wide-area assessment of NO 2 .…”