The spatial variation of O₃, NO, NO₂ and NO _x and the relation between them in two Swedish cities

Ozone and nitrogen oxides (NO _x ) are air pollutants with known associations to adverse health effects on humans. Few studies have simultaneously measured ozone and nitrogen oxides with high spatial resolution. The main aim of this paper was to assess the levels and variation of ground-level ozone, NO₂ and NO _x in two Swedish cities. An additional aim was to describe the levels of these pollutants within and between three different types of measurement sites (regional background, urban background and traffic sites) and within and between different measurement periods of the year. Three weekly sampling campaigns of NO _x and ozone were conducted simultaneously at 20 sites in two Swedish regions using Ogawa badges. Ozone was measured at 20 additional sites in each area. The median ozone concentration for all measurements was statistically significantly higher in Malmö (67 μg/m³) compared to Umeå (56 μg/m³), and in both cities, ozone levels were highest in April. Measurement period was a more important factor for describing the variation in ozone concentrations than the type of measurement site. The levels of NO₂ and NO _x were statistically significantly higher in the Malmö area (8.1 and 12 μg/m³) compared to the Umeå area (4.5 and 8.9 μg/m³). The levels were generally highest at the sites categorized as traffic, while the variability between different seasons was sparse.