Analysis of NO, NO2, O3 and NOx concentrations measured at a green area of Buenos Aires City during wintertime

We analyse the air quality data measured at a green area of Buenos Aires City (Argentina) during 38 days in winter. We study the relationships between ambient concentrations of nitric oxide (NO), nitrogen dioxide (NO2), ozone (O3) and nitrogen oxides (NOx=NO+NO2). The variation of the level of oxidant (OX=O3+NO2) with the NOx is obtained. It can be seen that the level of OX at a given location is made up of two contributions: one independent and another dependent on the NOx concentration. The first one can be considered as a regional contribution, equivalent to the background O3 concentration and the second one as a local contribution that depends on the level of primary pollution. Local oxidant sources may include direct NO2 emissions, the reaction of NO with O2 at high-NOx levels, and the emission of species that promote the conversion of NO to NO2. The final category of emissions may include the nitrous acid (HONO) that is emitted directly in vehicle exhaust. Finally, we present a diurnal variation of the local as well as regional contributions and the dependence of the last one on wind direction.