Measurement of local variations in atmospheric nitrogen dioxide levels in Sapporo, Japan, using a new method with high spatial and high temporal resolution

A nitrogen dioxide (NO2) monitoring system with an irreversible sensor has been developed. The sensor consists of a porous glass substrate impregnated with Saltzman reagents and the NO2 concentration is determined from the sensor’s light transmittance. The correlation coefficient for the NO2 concentration obtained with this device and that obtained with a commercial NOx analyzer was 0.79. A number of these devices were set up at the Sapporo Experimental Area in July 2001. Atmospheric NO2 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 NO2 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 NO2 concentration level, and the concentration decreased with distance from the intersection. The NO2 gradient generally tended to decrease with distance from the intersection, and the average NO2 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 NO2 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.