An analysis of the oxidant climatogy in the United Kingdom

• Main Author: Clapp, Lynette Joan
• Published: Imperial College London 2012
• Subjects: 363.738
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.556537

Ozone (03) and nitrogen dioxide (N02) are two of a series of air pollutants targeted in the UK Air Quality Strategy, by virtue of their adverse effects on human health and the natural environment. Because 03 and N02 are rapidly chemically inter-converted in the atmosphere, their behaviour is coupled and they can be collectively referred to as 'oxidant' (OX). Sources and trends of OX in the UK have been examined through a combination of dedicated field measurements of 03, N02 and nitric oxide (NO), over three years (January 2005 - December 2007) at the Silwood Park Atmospheric Research Station (SPARS) near Ascot; and through analysis of data for the same species at 31 sites across the UK, which are part of the UK Automatic Urban and Rural Network (AURN). SPARS measurements have contributed to data available from the London Air Quality Network (LAQN), the site being referred to as "Windsor and Maidenhead - Ascot" (MW3). Total Oxidant [OXh can be interpreted in terms of: (i) a Global hemispheric baseline, [OX]H, representing the baseline air transported into the UK; (ii) a Regional modification, [OX]R, which has contributions from production via regional-scale photochemical processing of emitted volatile organic compounds (VOC) and nitrogen oxides (NOx) , and loss via deposition; and (iii) a Local enhancement, [OX]L, from direct emissions of N02 (e.g., road vehicle exhaust). Separation of these components involved an air mass screening methodology, using back-trajectories calculated with meteorological models. [OX]H makes the major contribution to [OXh at rural and polluted urban centre sites, although either of the other components can dominate during episodes. [OX]R is typically enhanced during the period from April to September when meteorological conditions are favourable and photochemical processes operate efficiently. [OX]L is largest at polluted urban sites close to emission sources, and maximises in the winter months when dispersion is least efficient. Abstract Annual mean data since the 1990s show an increasing trend for [OX]H (a consequence of increasing emissions of methane and NOx), while [OX]R and [OX]L show decreasing trends because of emissions control strategies within the EU and UK. Seasonal and spatial variations in [OX]H and [OX]R are valuable for forecasting and modelling 03. [OX]H is important for policy when baseline 03 concentrations exceed international air quality standards.