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The levels of ozone (O3) at a given location in the UK have been reported to be determined by a combination of global (northern hemispheric), regional and local-scale effects. These effects therefore also potentially influence values of the O3 exposure metric, AOT40 (the accumulated ozone exposure over a threshold of 40 ppb). A corresponding background oxidant metric, AOXBT40, is defined, which quantifies the value of AOT40 corrected for the effects of local oxidant sources and the chemical coupling of O3 with emitted NOx (i.e. effectively a remote rural background AOT40 value). Data from the UK automatic monitoring network have been analysed to determine values of AOT40 and AOXBT40 at 39 UK sites for the example year of 2009. The spatial variation of AOXBT40 over the UK is consistent with contributions deriving both directly from the northern hemispheric baseline O3 level and from episodic events during which the baseline is supplemented by regional-scale oxidant formation; and the approximate relative importance of these inputs is estimated. The fractional decrement in AOT40 (AOT40/AOXBT40), shows a well-defined dependence on the average NOx level for the hours that contribute to AOXBT40, consistent with the expected impact of the local-scale chemical coupling of O3 and NOx. The AOXBT40 concept can therefore be used to help characterise the factors that control AOT40 on different spatial scales, and its potential applications in empirical O3 exposure modelling activities and model evaluation are briefly discussed. [ABSTRACT FROM AUTHOR]

Data from the UK automatic monitoring network have been analysed to investigate average trends in ozone concentrations, concentration distributions and exceedences of the public information threshold (180μgm−3) at 13 rural sites (over the period 1990–2006) and at five urban sites (over the period 1993–2006) throughout the UK. The data indicate that the observations at a given location in the UK can be influenced by a combination of global (hemispheric)-, regional- and local-scale effects. As a result, the observed trend in the ozone metrics is determined from the net trend of these three influences, the relative contributions of which can vary both spatially and temporally. Specifically, the data reflect the following three major influences: (i) a gradual increase in the hemispheric baseline ozone concentration resulting from global-scale effects, thereby influencing the baseline levels of ozone brought into the UK from the Atlantic Ocean; (ii) substantial short-term elevations in ozone concentrations during summertime episodes, resulting from the formation of additional ozone from regional-scale photochemical processing of emitted VOC and NO x over north-west Europe, with such events tending to be more frequent and intense towards the south and east of the UK. On average, the severity of such events has progressively decreased since about 1990, as a result of EU controls of anthropogenic VOC and NO x emissions; and (iii) local-scale removal of ozone by direct reaction with emitted NO has gradually decreased, as a result of the control of NO x emissions. This has resulted in a general increasing influence on ozone concentrations since about 1990, which is most apparent at urban sites, where NO x emissions are higher, but also influences the observations at the majority of rural locations. [Copyright &y& Elsevier]

The monitoring of metals in ambient air has been undertaken for over 40 years on a national basis in the UK. During this period, the UK pollution landscape has continued to evolve in terms of emission sources, and the measurement framework for metals in ambient air, the UK Heavy Metals Monitoring Network, has also been subject to significant configuration changes. Therefore, this work provides a timely review of more recent concentration trends in the context of current emission profiles. Overall, throughout this time period, there has been a significant downward trend in the emissions and consequently, the measured concentrations of most metals in UK ambient air. Ambient concentrations were generally found to be well correlated with emission estimates. Analysis of the sensitivity of measured concentrations to emissions suggests that concentrations have fallen faster than the reduction in emission estimates would have predicted at typical median urban background sites. [ABSTRACT FROM AUTHOR]