High and low NOx chemistry in the troposphere. Implementing the use of indicator species in a trajectory model

Ground level ozone is considered to be an important environmental threat affecting human health negatively and causing damage to vegetation. Ozone is produced from nitrogen oxides (NOx) and volatile organic compounds (VOC) in the presence of sunlight. The only way to reduce ozone is to reduce the emissions of the precursors. There are two different chemical states in the troposphere, referred to as low and high NOx chemistry. In the low NOx areas, the ozone is limited by the availability of NOx, while in the high NOx areas, it is the VOC which limits the production of ozone. The use of indicator species, as a way to decide the chemical state the troposphere, has been investigated using the IVL trajectory model. The concept has previously been tested for US conditions in a 3D model. The study show that the concept of indicator species can be implemented in a trajectory model. The values of the indicator species for the transition from high to low NOx have been estimated for European conditions and have shown a reasonable agreement with the previous findings in the US