A statistical analysis was carried out to evaluate the relationship between NO
2 concentration and traffic density. Environmental monitoring NO
2 concentration data were obtained by diffusive sampler method between April, 1989 and March, 1993 at 22 monitoring site in Sendai City.
The average monthly NO
2 concentration at all the sites ranged from 14.4 ppb to 38.9 ppb (mean, 27.2 ppb) . The annual distribution of monthly adjusted treatment means for NO
2 concentration formed a V-shaped curve, with the lowest value observed in August and the highest in March. The pattern of monthly change of NO
2 concentration in Sendai City was similar to that reported for areas with high atmospheric NO
2 concentration. Analysis of covariance revealed the greatest effect for traffic density. The partial regression coefficient for traffic density was 2.2×10
-4 (ppb/vehicle), indicating that an increase of NO
2 concentration on the order of 2.2 ppb could be predicted for every traffic density increase of 10, 000 vehicles. The partial regression coefficient for distance to the road was -0.1 ppb/m. Partial regression coefficient for measurement year was significant and showed positive value (0.32 ppb/year) . However, the magnitude of annual increase (1.2%) is low. About 63% of the total observed variance could be accounted for by the mathematical model used in this study.
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