This report is an attempt to investigate the background to the high NO2 levels in Gothenburg and the reason for the slowing decrease in NO2 observed during the last years. Two possible reasons for these observations are investigated: contribution from shipping to NO2 emissions, and increased fraction of NO2 in the NOX emissions from modern diesel engines. The issue was studied through emission measurement, passive sampling, dispersion modelling and atmospheric chemistry studies Two possible reasons for the high NO2 levels in Gothenburg were investigated: 1) increased fraction of NO2 in the NOX emissions from modern diesel engines, and 2) increasing total emission of NOX due to increasing contribution from shipping. The results also showed that local mixing conditions greatly influenced the dispersion of especially local and ground-based emissions This was mainly due to their main location within the Göta älv valleys where the dispersion becomes particularly poor during high pressure conditions. The effect of ship emissions in the Gothenburg area was very dominant along the harbour.