Abstract A nitrogen dioxide (NO 2 ) monitoring system with an irreversible sensor has been developed. The sensor consists of a porous glass substrate impregnated with Saltzman reagents and the NO 2 concentration is determined from the sensor’s light transmittance. The correlation coefficient for the NO 2 concentration obtained with this device and that obtained with a commercial NO x analyzer was 0.79. A number of these devices were set up at the Sapporo Experimental Area in July 2001. Atmospheric NO 2 concentrations recorded from 9 to 22 July 2001 are described in terms of local spatial variations and in relation to differences in distance from a roadway intersection. At most sites the NO 2 level fluctuated throughout the day, and the general pattern consisted of a high level in the morning and evening and a low level during the night and in the afternoon. Proximity to road traffic increased the mean NO 2 concentration level, and the concentration decreased with distance from the intersection. The NO 2 gradient generally tended to decrease with distance from the intersection, and the average NO 2 concentrations over half a day and over 1 day at the intersection were respectively 50% and 36% higher than the concentration 150 m from the intersection. We also investigated the relationships between NO 2 levels, local meteorological conditions and the location conditions. At a measurement point on the side of a high building, the concentration was high when the measurement point was sheltered and low when it was exposed to the wind. The influence of a high building extends over a range of tens of meters, which is equal to the height of the building.
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