Field validation of the Ogawa diffusive sampler for NO2 and NOx in a cold climate

Abstract

A small-scale field trial in Umeå, Sweden with Ogawa samplers and a chemiluminescence instrument indicated that the NO(2) concentration was underestimated with respect to the reference monitor, if calculated according to the manufacturer's Ogawa sampling protocol. By co-locating Ogawa samplers and reference monitors at six sites in two Swedish cities, uptake rates were determined for NO(2) and NO(x) better applicable to the Swedish conditions and climate. The concentrations of NO(2) and NO(x) calculated according to the instruction manual of the sampler and using the field-determined uptake rates were compared with values derived from chemiluminescence monitors for each week over which samples were taken. When calculated according to the manufacturer's suggested protocol, the Ogawa sampler underestimated the NO(2) concentrations by 9.1% on average for all samples (N = 53), with respect to the reference monitor. In contrast, NO(x) concentrations were overestimated by a mean value of 15% for all samples (N = 45). By using the field determined uptake rates for the calculation of NO(2) and NO(x) a better estimation of the concentrations was obtained. The ratio between concentrations determined with the Ogawa samplers and chemiluminescence monitors was then 1.02 for all measurements of NO(2) and 1.00 for NO(x). Precision, expressed as the mean coefficient of variation, was 6.4% for six, 6-replicate measurements of NO(2) and 3.7% for five, 6-replicate measurements of NO(x).

Assessing traffic and industrial contributions to ambient nitrogen dioxide and volatile organic compounds in a low pollution urban environment

“…Observed concentrations from the four passive samplers collocated with NAPS stations (two per season) were positively biased during the fall and negatively biased during the spring. Further research is required to understand if this was a systemic bias related to temperature or other environmental differences during the two monitoring campaigns, but Hagenbjork-Gustafsson et al (2010) show that Ogawa samplers can yield inconsistent results when compared to continuous chemiluminescence monitors. Nonetheless, the pooled data showed a high consistency with annual NAPS averages for all pollutants as well as high correlations with seasonal measurements, suggesting that the pooled data are representative of longer term concentration levels.…”

An assessment of air pollution and its attributable mortality in Ulaanbaatar, Mongolia

“…All NO 2 concentrations were above the LOD; two SO 2 measurements below the LOD (2.5 ppb) were assumed to have a concentration of 1.25 ppb (LOD/2). We colocated our Ogawa monitors with government monitors at three locations, but adjustment of the Ogawa measurements, which are known to underestimate NO 2 concentrations at cold temperatures (Hagenbjork-Gustafsson et al 2010), was not possible due to large gaps in the government data during the 2 weeks of Ogawa monitoring. NO 2 and SO 2 were normally distributed with mean (±SD) concentrations of 10.7 ± 5.8 and 17.0 ± 11.8 ppb, respectively, and the two pollutants were moderately correlated ( r  = 0.50; p  < 0.01).…”

The spatial variation of O3, NO, NO2 and NO x and the relation between them in two Swedish cities

“…This could be an issue when comparing measurement periods between the two areas. Ogawa samplers used in the study have been used in earlier studies (Gibson et al 2009; Hauser et al 2015; Jerrett et al 2009; Mukerjee et al 2009) and are considered to be a reliable technique to measure ozone and NO x (Bhangar et al 2013; Hagenbjork-Gustafsson et al 2010; Sather et al 2007). …”

“…The sampling and the subsequent ion chromatography analysis of NO 2 , NO x and ozone, respectively, have been described in detail previously (Hagenbjork-Gustafsson et al 2010; Malmqvist et al 2014). In short, the Ogawa sampler has a cylindrical body with two ends, which enables simultaneous monitoring of NO 2 and NO x .…”