Quantifying the spatial distribution of surface ozone concentration in the UK

A study of ozone concentration measurements at 20 rural sites throughout the UK has enabled the identification of the major variables controlling surface ozone concentrations (wind velocity, topography and local NO sources). Empirical methods to quantify the spatial pattern in surface concentrations at 1 km resolution, incorporating these influences, are developed. The procedure maps ozone concentrations from the period of the day when measurements are representative of large areas of countryside. In these conditions, rural monitoring sites (∼100 km apart) are highly correlated ( r 2⩾0.8) and least affected by local site characteristics. The effects of boundary layer stability are quantified using the observed relationship between the diurnal variability of surface ozone concentration and altitude. This allows the detailed structure in rural concentrations to be quantified. An urban correction, to account for the gas phase titration of surface ozone by local NO sources, is added to the mapping procedure based on the relationship between urban ozone concentration measurements and those in rural areas. The spatial distribution of the annual average ozone concentration and the accumulated ozone concentration over a threshold of 40 ppb (AOT40) are calculated from UK measurements. Simple assessments of the effects of ozone on materials and vegetation are made. Although 87% of the UK exceeds the critical level for materials (20 ppb annual average), this is less than 0.1% of urban areas and so the risk of damage is probably small. For crops and semi-natural vegetation, the critical level (AOT40 3000 ppb h May–July daylight hours) is exceeded over 71% of the UK; for forests, the critical level (10,000 ppb h April–September daylight hours) is exceeded over 8% of the country. This indicates the potential for effects on large areas of crops and semi-natural vegetation but only small areas of forest.