Spatial and temporal variation of O3, NO and NO2 concentrations at rural and urban sites in Marmara Region of Turkey

Abstract

The first continuous measurements of the hourly surface ozone (O3), nitric oxide (NO) and nitrogen dioxide (NO2) concentrations at 7 rural and 15 urban sites in Marmara Region of Turkey during the period from March 2013 to April 2016. The results indicate that surface O3 is an extensive problem throughout the Marmara Region. O3 levels have similar seasonal pattern in rural and urban sites by following the order of summer, spring, fall, and winter. The seasonal results showed an opposite behaviour among O3 and NOx (NO + NO2) in both rural and urban sites, marked by maximums (minimum NOx) of O3 in summer and minimums (maximum NOx) in fall and winter. The summer concentrations vary between 91.5 and 123.6 μg/m3 and 74.6–112.4 μg/m3 at rural and urban sites respectively. Furthermore, O3 peak concentration time in rural areas in O3 seasons (April–September) occurred at around 17:00–18:00 LST while in urban areas at around 15:00–16:00 LST, respectively. Air quality standards for O3 concentrations in Sile and Yalova rural sites were significantly exceeded during O3 season. This exceedance made a linkage between back trajectories and air masses with respect to the O3 levels. 72-hr back trajectories at an altitude of 500 m agl were computed by HYSPLIT model to assess the type of air masses which reach the area. AOT40 (accumulated exposure over a threshold of 40 ppb) index was performed for both vegetation and forestry standards and EU Directive were significantly exceeded at all rural stations.