Quality assurance of automatic nitrogen oxide analyzers and their application to field analysis

After automatic nitrogen oxide analyzers were calibrated, nitrogen oxides i n the air were analyzed in the field by 14 calibrated automatic analyzers t o examine the compatibility of measurement data. The 14 analyzers, calibrat ed with an equivalent liquid (static), showed nearly identical coefficients of variation over the range of 0.3 to 1.2%. However, those calibrated with a standard gas (dynamic) showed 99.7 +/- 0.35% of the collection rate of n itrogen dioxide (NO2) and 79.2 +/- 2.7% of the oxidation rate of nitrogen m onoxide (NO) and 3.4% of the coefficient of variation, similar to that in t he static calibration. The same air sample was introduced into the 14 analy zers for 24h for a comparison. A mean NO concentration of 11 +/- 0.55 ppb w ith a coefficient of variation of 5.0%, and mean NO2 concentration of 25 +/ - 0.53 ppb with coefficient of variation of 2.1% were achieved, respectivel y. The concentration of nitrogen oxides was analyzed at the same time aroun d Route 1 (traffic: 60000 vehicle/day), a typical principal road in the Met ropolitan area, in all seasons by the 14 analyzers mentioned above. The con centration of NO2 was nearly the same at 0 m and 150 m from the road side d uring all seasons, but was slightly lower in the summer. On the contrary, t he mean concentration of NO during 2 weeks was 75 ppb at 0 m and approximat ely 40 ppb at 50 m or more from the roadside in the winter. A direct effect of NO emitted fi urn the vehicles on the NO concentration was obserbed at a distance of up to 50 m.