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Abstract: It is generally accepted that uncertainty should be taken into account in environmental assessments and the subsequent decision-making. This paper undertakes an uncertainty assessment for acidity and nutrient nitrogen critical loads and their exceedances, which is important in determining national and international policy on the emissions of acidifying air pollutants. This is the first time such an analysis has been done for the UK at the national scale. In this paper we illustrate the process and issues with reference to “managed coniferous woodland”, one of a number of habitat types for which critical loads are calculated. Again using coniferous woodland as an example Monte Carlo analysis showed that the uncertainties in the national critical loads varied between 14 and 29%. Policy makers are however primarily concerned with whether the critical load is exceeded and therefore the uncertainty in exceedance is also estimated. Again using coniferous woodland as an example, Monte Carlo analysis showed that for acidity, it was uncertain whether the critical load was exceeded or not for the majority of the coniferous woodland habitat. For nutrient nitrogen, most of the habitat had a very high probability of exceedance. [Copyright &y& Elsevier]

The fishing industry is heavily reliant on the use of fossil fuel and emits large quantities of greenhouse gases and other atmospheric pollutants. Methods used to calculate fishing vessel emissions inventories have traditionally utilised estimates of fuel efficiency per unit of catch. These methods have weaknesses because they do not easily allow temporal and geographical allocation of emissions. A large proportion of fishing and other small commercial vessels are also omitted from global shipping emissions inventories such as the International Maritime Organisation's Greenhouse Gas Studies. This paper demonstrates an activity-based methodology for the production of temporally- and spatially-resolved emissions inventories using data produced by Automatic Identification Systems (AIS). The methodology addresses the issue of how to use AIS data for fleets where not all vessels use AIS technology and how to assign engine load when vessels are towing trawling or dredging gear. The results of this are compared to a fuel-based methodology using publicly available European Commission fisheries data on fuel efficiency and annual catch. The results show relatively good agreement between the two methodologies, with an estimate of 295.7 kilotons of fuel used and 914.4 kilotons of carbon dioxide emitted between May 2012 and May 2013 using the activity-based methodology. Different methods of calculating speed using AIS data are also compared. The results indicate that using the speed data contained directly in the AIS data is preferable to calculating speed from the distance and time interval between consecutive AIS data points. [ABSTRACT FROM AUTHOR]

Elevated surface ozone during heatwaves and recent hot summers raises concerns over the potential for climate change to exacerbate ozone air pollution in the UK. In this paper, we perform a robust statistical analysis of four decades worth of daily maximum 8-h (MDA8) ozone measurements from the UK's Automated Urban and Rural Network. A temperature dependent extreme value model is developed to characterise the magnitude and frequency of extreme ozone events and to determine probabilities for ozone exceeding health thresholds, as defined in the UK's air quality index. Our model is found to describe the tails of the MDA8 ozone distributions well at all 119 monitoring sites considered. For the decade 2010–2019, we estimate that >90% of sites have a 1-year MDA8 ozone return level greater than the 'moderate' ozone threshold of 100 μg/m3. We also find that 33% of sites are currently expected to breach the UK government's national air quality objective that MDA8 ozone should not exceed 100 μg/m3 more than ten times per year. We estimate the present overall probability of MDA8 ozone exceeding 100 μg/m3 on a given day to be between <0.1% and 5.4%, depending on site, with averages of 2.7% (rural) and 1.6% (urban background locations). Our analysis reveals a significant decline over time in the likelihood of the UK experiencing extreme ozone episodes, with 1-year return levels in the 1980s now roughly comparable to 10-year return levels in the present. Similarly, probabilities of MDA8 ozone exceeding 100 μg/m3 have decreased by a factor of ∼2–6 since the 1980s in some locations. However, our results also highlight a strong positive temperature dependence to the risk of ozone exceedances. In consequence, increasingly hot summers due to climate change may offset some of these gains. • Extreme value analysis used to quantify probability of UK extreme ozone episodes. • Considerable decline in likelihood of UK experiencing extreme ozone episodes. • Reduced probability of ozone exceeding 'moderate' health threshold (100 μg/m3). • Non-linear increase in risk of extreme ozone with unusually high temperatures. [ABSTRACT FROM AUTHOR]

Abstract: This paper shows how the advanced chemical transport model CMAQ can be used to estimate future levels of PM2.5 in the UK, the key air pollutant in terms of human health effects, but one which is largely made up from the formation of secondary particulate in the atmosphere. By adding the primary particulate contribution from typical urban roads and including a margin for error, it is concluded that the current indicative limit value for PM2.5 will largely be met in 2020 assuming 2006 meteorological conditions. Contributions to annual average regional PM2.5 concentration from wild fires in Europe in 2006 and from possible climate change between 2006 and 2020 are shown to be small compared with the change in PM2.5 concentration arising from changes in emissions between 2006 and 2020. The contribution from emissions from major industrial sources regulated in the UK is estimated from additional CMAQ calculations. The potential source strength of these emissions is a useful indicator of the linearity of the response of the atmosphere to changes in emissions. Uncertainties in the modelling of regional and local sources are taken into account based on previous evaluations of the models. Future actual trends in emissions mean that exceedences of limit values may arise, and these and further research into PM2.5 health effects will need to be part of the future strategy to manage PM2.5 concentrations. [Copyright &y& Elsevier]

Abstract: Particulate matter remains a challenging pollutant for air pollution control in the UK and across much of Europe. Particulate matter is a complex mixture of which secondary inorganic compounds (sulphates, nitrates) are a major component. This paper is concerned with taking a basic version of the UK Photochemical Trajectory Model and enhancing a number of features in the model in order to better represent boundary layer processes and to improve the description of secondary inorganic aerosol formation. The enhancements include an improved treatment of the boundary layer, deposition processes (both wet and dry), attenuation of photolysis rates by cloud cover, and inclusion of the aerosol thermodynamic model ISORROPIA II to account both for chemistry within the aerosol and between the particles and gas phase. Emissions inventories have been updated and are adjusted according to season, day of the week and hour of the day. Stack emissions from high level sources are now adjusted according to the height of the boundary layer and a scheme for generating marine aerosol has been included. The skill of the improved model has been evaluated through predictions of the concentrations of particulate chloride, nitrate and sulphate and the results show increased accuracy and lower mean bias. There is a much higher proportion of the values lying within a factor of 2 of the observed values compared to the basic model and Normalised Mean Bias has reduced by at least 89% for nitrate and sulphate. Similarly, the Index of Agreement between calculated and measured values has improved by ∼10%. Considering the contribution of each enhancement to the improvement in the performance metrics, the most significant enhancement was the replacement of the parameterisation of the boundary layer height, relative humidity and temperature by HYSPLIT values calculated for each trajectory. The second most significant enhancement was the parameterisation of the photolysis rates by values calculated by an off line database accounting for the dependence of photolysis rates on zenith angle, cloud cover, land surface type and column ozone. The inclusion of initial conditions which were dependent on the starting point of the trajectory and the modulation of stack emissions made the most significant improvement to sulphate. Furthermore, in order to assess the model''s response to abatement scenarios, 30% abatements of either NH3, NOx or SO2 showed a reduction in the sum of chloride, nitrate and sulphate of between 3.1% and 8.5% (with a corresponding estimated reduction of 1.6–3.7% reduction in PM10). The largest reduction in this contribution is due to the abatement of NOx. [Copyright &y& Elsevier]

Abstract: In this paper we have compared detailed road traffic NOx emissions with the equivalent trends in ambient roadside NOx measurements. This was undertaken separately in Great Britain and London, for all of the major roads, and by road type and location. The emissions trends were created using different emissions factors, those used in UK emissions inventories (Base case), the Swiss-German handbook (HBEFA), and those created from recent remote sensing measurements in the UK (RSD). An alternative assumption for use of Selective Catalytic Reduction (SCR) in the articulated Heavy Goods Vehicle (HGV) fleet was also tested. For all scenarios traffic flows, speeds and vehicle age were kept constant. Comparison between the emissions scenarios in Great Britain showed that by 2009, NOx emissions estimates from road traffic could be as much as 25% greater than current UK estimates and 31% greater in London. The RSD emissions inventory gave the smallest downward trend in NOx emissions, from 2004 to 2009, of between 3 and 4%/year and this compared with a reduction of ∼6%/year from the Base Case and HBEFA scenarios. All scenarios compared poorly with roadside NOx measurement trends from UK sites, which typically reduce by between 1% and 2%/year. We have shown that the differences in NOx emissions trends were driven, partially at least, by the relative contribution from light duty diesel vehicles. An analysis from 2700 NOx measurement sites throughout Europe has shown that this problem is unlikely to be limited to the UK, and identifies a difficulty in meeting EU limit values for NO2, obligations under the National Emission Ceilings Directive () and the Gothenburg Protocol () and for forecasting future changes in PM2.5. [Copyright &y& Elsevier]

Abstract: The Ozone Source–Receptor Model (OSRM) is a Lagrangian trajectory model developed to describe photochemical ozone production in the UK. The OSRM builds on existing boundary layer trajectory models used previously for assisting the development of UK ozone policy, but has a number of notable differences. A novel feature of the OSRM is a surface conversion module to represent the vertical gradient in ozone arising from chemical loss and deposition to the surface. This has significantly improved the performance of the model, especially in urban areas. In this paper, the modelling system is described and its performance against measured ozone concentrations and metrics and other UK ozone models is discussed. The model has been used to calculate future ozone concentrations in the UK and thus to assess a number of possible control measures developed for the UK Air Quality Strategy. [Copyright &y& Elsevier]

Abstract: This paper describes the further development and application of the Edinburgh–Lancaster Model for Ozone (ELMO). We replace straight-line back-trajectories with trajectories and associated meteorology supplied by the US National Oceanic and Atmospheric Administration Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) service to allow more realistic modelling of specific UK ozone episodes. We call this ELMO-2. Model performance is rigorously tested against observed ozone concentrations for two episodes recorded across 14 rural UK monitoring stations during the spring and summer of 1995. For both episodes, the afternoon concentrations (usually coinciding with the daily maxima) are captured well by the model and the diurnal ozone cycle is reproduced, although the amplitude in concentrations is generally smaller than the observed. The summer episode is investigated further through indicator species analysis and source attribution, and found to be mainly VOC-limited. European emissions account for the majority of ozone production. We demonstrate how improved modelling leads to better understanding of regional and local ozone production across the UK under episodic conditions. [Copyright &y& Elsevier]

Abstract: In this paper the meteorological processes responsible for transporting tracer during the second ETEX (European Tracer EXperiment) release are determined using the UK Met Office Unified Model (UM). The UM predicted distribution of tracer is also compared with observations from the ETEX campaign. The dominant meteorological process is a warm conveyor belt which transports large amounts of tracer away from the surface up to a height of 4 km over a 36 h period. Convection is also an important process, transporting tracer to heights of up to 8 km. Potential sources of error when using an operational numerical weather prediction model to forecast air quality are also investigated. These potential sources of error include model dynamics, model resolution and model physics. In the UM a semi-Lagrangian monotonic advection scheme is used with cubic polynomial interpolation. This can predict unrealistic negative values of tracer which are subsequently set to zero, and hence results in an overprediction of tracer concentrations. In order to conserve mass in the UM tracer simulations it was necessary to include a flux corrected transport method. Model resolution can also affect the accuracy of predicted tracer distributions. Low resolution simulations (50 km grid length) were unable to resolve a change in wind direction observed during ETEX 2, this led to an error in the transport direction and hence an error in tracer distribution. High resolution simulations (12 km grid length) captured the change in wind direction and hence produced a tracer distribution that compared better with the observations. The representation of convective mixing was found to have a large effect on the vertical transport of tracer. Turning off the convective mixing parameterisation in the UM significantly reduced the vertical transport of tracer. Finally, air quality forecasts were found to be sensitive to the timing of synoptic scale features. Errors in the position of the cold front relative to the tracer release location of only 1 h resulted in changes in the predicted tracer concentrations that were of the same order of magnitude as the absolute tracer concentrations. [Copyright &y& Elsevier]

CORINAIR atmospheric emission inventories are frequently used input data for air quality models with a domain situated in Europe. In CORINAIR emission inventories, sources are broken down over 11 major source categories. This paper presents spatial surrogates for the disaggregation of CORINAIR atmospheric emission inventories for input of air pollutants and particulate matter to grid or polygon based air quality model domains inside Europe. The basis for the disaggregation model was the CLC2000 land cover data to which statistical weights were added. Weights were population census data for residential emissions, employment statistics for agricultural and industrial area emissions, livestock statistics for ammonia emissions and annual aircraft movements for emissions realized by air transport. Additional road and off-road network information was used to disaggregate emissions realized by traffic. A comparison of top down produced emission estimates with spatially resolved national emission data for The Netherlands and the United Kingdom gave confidence in the present spatial surrogates as a tool for the top down production of atmospheric emission maps. Explained variance at a spatial resolution of 5km was >70% for CO, NMVOC and NO x , >60% for PM10 and almost 50% for SO2. [Copyright &y& Elsevier]

This paper considers the evolution of attempts to control and manage air pollution, principally but not exclusively focussing upon the challenge of managing air pollution in urban environments. The development and implementation of a range of air pollution control measures are considered. Initially the measures implemented primarily addressed point sources, a small number of fuel types and a limited number of pollutants. The adequacy of such a source-control approach is assessed within the context of a changing and challenging air pollution climate. An assessment of air quality management in the United Kingdom over a 50-year timeframe exemplifies the range of issues and challenges in contemporary air quality management. The need for new approaches is explored and the development and implementation of an effects-based, risk management system for air quality regulation is evaluated. [Copyright &y& Elsevier]

Measurements of mercury in ambient air are assuming greater importance, because of increasing health concerns and European legislation. In order to have confidence in measured values and to assess compliance with target values, measurements must be made with validated methodologies which have traceable uncertainty statements associated with them. This paper presents a practical uncertainty budget for the measurement of vapour-phase mercury in ambient air, sampling onto a gold-coated silica adsorption tube and measuring with atomic fluorescence spectrometry. Moreover, this budget may be generalised for other related measurement methods for mercury vapour and other ambient air pollutants. All significant sources of uncertainty are discussed and estimated. Expanded relative uncertainties at the 95% confidence interval of approximately 17% are estimated for exemplar measurements made by the National Physical Laboratory (NPL) as part of the UK Heavy Metals Monitoring Network. [Copyright &y& Elsevier]