NIGHTLY OZONE CONCENTRATIONS AT GROUND LEVEL IN THE MIDWEST OF BRAZIL: NO AND NO2 CONCENTRATION ASSIGNMENTS

The contribution of the precursors nitric oxide (NO), nitrogen dioxide (NO 2 ), and meteorological factors were evaluated in relation to the formation of nocturnal O 3 in Campo Grande – MS, Brazil. The maximum nocturnal level identified in the study for NO 2 , NO, and O 3 were 49.5, 58.0, and 30.0 μg.m -3 ,followed by the minimum values of 10.0, 6.0, and 9.0 μg m -3 and averages of 27.4, 21.2, and 18.3 μg m -3 , respectfully. The effect of NO 2 and NO titration emitted by anthropic sources in the urban area, which has the highest levels of NO 2 and NO in comparison with other locations, may be the main driving force of the lowest nocturnal O 3 value. During the night, O 3 titration at ground level occurred, resulting in the average value of the  ratio, recorded as 25.6 with maximum and minimum values of 35.4 and 19.8 μg m -3 . It suggests that urban locations with wind speeds values of positive   can lead to the accumulation of O 3 at night. The average ratio between the concentration of nocturnal ozone and diurnal surface ozone for Campo Grande was 55%.