Influence of the North Atlantic Oscillation on European tropospheric composition: an observational and modelling study

Abstract

We have used satellite observations and a simulation from the TOMCAT chemistry transport model (CTM) to investigate the influence of the well-known winter-time North Atlantic Oscillation (NAO) on European tropospheric composition. Under the positive phase of the NAO (NAO+), strong westerlies tend to enhance transport of European 5 pollution (e.g. nitrogen oxides, NO x , carbon monoxide, CO) away from anthropogenic source regions. In contrast, during the negative phase of the NAO (NAO-), more stable meteorological conditions lead to a build up of pollutants over these regions, relative to the winter-time average pollution levels. However, the secondary pollutant ozone shows the opposite signal of larger values during NAO+. NAO+ introduces Atlantic