Analysis of NO, NO2, NOx, O3 and oxidant (OX = O3 + NO2) levels measured in a metropolitan area in the southwest of Iberian Peninsula

Concentrations of O3, NO, NO2, NOx and oxidant (OX = O3 + NO2) were investigated for the first time, in the southwest of the Iberian Peninsula, in the Seville metropolitan area, during 2004. This area experiences frequent photochemical pollution events, mainly in the warm season. Two different environments were analyzed and compared, an urban traffic station (Torneo) and a suburban station (Aljarafe). The concentration of OX (defined as O3 + NO2) can be described in terms of the sum of a NOx-independent ‘regional’ contribution (i.e. the O3 background), and a linearly NOx-dependent ‘local’ contribution. Monthly dependence of regional and local OX concentration variation at Torneo and Aljarafe stations were studied along with the annual variation of the daily mean NOx and OX. Maximum levels of OX > 190 μg m− 3 where NOx < 70 μg m− 3 at Aljarafe, and OX < 170 μg m− 3 with NOx around 80–90 μg m− 3 can be expected in summer months and during daylight hours. Also during summer, but at night, more elevated NOx levels are needed in order to achieve maximum OX values (OX = 130–150 μg m− 3 with NOx ≥ 100 μg m− 3 at Aljarafe, OX = 110–130 μg m− 3 with NOx ≥ 100 μg m− 3 at Torneo). This can be used as an approximation to estimate the OX concentrations in Seville for each month, as a function of the NOx measured, as well as to improve in the atmospheric photochemical dynamic in the Spanish Western Mediterranean area where there are undeniable air quality problems.