Factors which could have an adverse impact on measurement quality, such as shadows of roadside trees, bridges and buildings, daily and seasonal variations in the elevation of the sun, road gradient and vehicle speed, were eliminated by measurement and evaluation procedures. The data were compared with those recorded by a radiation measurement station located outside the city area.
On average, the global radiation flux density in the city area was 5.3 % (s=1,8 %) lower than in the surrounding area; the reduction was 7.1 % in the spring and 4.0 % in the summer. The differences are significant with an error probability of 5 %. As regards the distribution patterns of global radiation flux density, all the test trips showed very good agreement. The variation between average values measured on sections and the values of the station in the surrounding area ranged from -11 % to +0.2 %. The reasons are explained by plausibility considerations (effects of different wind directions, busy motorway intersections, industrial areas in the vicinity, humidity etc.) and the data are compared with results found in other publications.
In order to investigate the causes, correlations were also computed between the concentrations of atmospheric constituents (NO, NO2, O3, CO2) and the radiation attenuation measured at the same time. The partial correlation coefficients show that there is no significant relationship between the trace substances measured and the global radiation flux density.
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