Regional air quality and impacts of large point sources

Air pollution episodes can lead to exceedances of national and European standards and limit values. In general, episodes tend to occur during stagnant meteorological conditions with limited vertical mixing and low wind speeds.  Of particular concern to regulators such as the UK’s Environment Agency is how emissions (for example, from power station stacks) contribute to unusually high levels of pollutants such as SO2, NO2, and O3 over regional scales.

A significant challenge for the control of secondary pollutants, such as O3 and their precursors is related to the oxidation processes, which introduce non-linearity between the emissions of primary pollutants and the resulting concentrations. As a ‘secondary’ pollutant, O3 is formed through complex reactions involving sunlight, nitrogen oxides (NOx), and volatile organic compounds (VOCs). Consequently, it is necessary to understand how ozone depends on NOx and VOC in order to develop an effective policy response. As part of a project funded by the UK’s Environment Agency, the modelling system MM5/CMAQ has been applied for the first time to study a range of air pollution cases affecting the UK.  New studies with the NAMEIII model were conducted at the Met Office, also as part of this project, to investigate the plume chemistry affecting ozone on regional scales.

Acknowledgements & collaborations:

This work was funded by the UK Environment Agency and the European Commission (Air4EU FP6 project). BADC and DEFRA are thanked for providing access to meteorological and air quality data respectively. The collaboration of the UK Met Office is also appreciated. 

Selected references: Yu, Y., R. S. Sokhi, D. R. Middleton, 2007. Estimating contributions of Agency-regulated sources to secondary pollutants using CMAQ and NAME III models. Environment Agency Research Report.