Tropospheric ozone concentrations - Seasonal and daily analysis and its association with NO and NO2 as a function of NOx in Ciuc depression – Romania

Abstract

This paper summarizes the results of a yearlong continuous measurements of gaseous pollutants, NO, NO2, NOxand O3 in the ambient air of Ciuc Depression. Measured concentration of the pollutants in study area is a function of time. NO, NO2 and O3 peak occurred in succession in presence of sunlight. At the time of maximum O3 concentration most of the NOx are utilized. The diurnal cycle of ground level ozone concentrations, revealed mid-day peak with lower nocturnal concentrations and inverse relationship exists between O3 and NOx, which are evidences of photochemical O3 formation. Particular emphasis is placed on establishing how the level of 'oxidant', OX (taken to be the sum of O3 and NO2) varies with the level of NOx, and therefore to gain some insight into the atmospheric sources of OX. The analyses indicate that the level of OX at a given location is made up of NOx- independent and NOx- dependent contributions. The former is effectively a regional contribution which equates to the regional background O3 level, whereas the latter is effectively a local contribution which correlates with the level of primary pollution. Increased values can be also observed for more periods of the year; this fact for the depressional case of Ciuc are due to the particular case represent by stable boundary layer conditions (high static stability conditions in term of Brunt - Vaisala frequency) which are long known for causing increasing concentration of pollutant concentrations.