Stephen Hallsworth

Predictions of U.K. Regulated Power Station Contributions to Regional Air Pollution and Deposition: A Model Comparison Exercise

ABSTRACT Contributions of the emissions from a U.K. regulated fossil-fuel power station to regional air pollution and deposition are estimated using four air quality modeling systems for the year 2003. The modeling systems vary in complexity and emphasis in the way they treat atmospheric and chemical processes, and include the Community Multiscale Air Quality (CMAQ) modeling system in its versions 4.6 and 4.7, a nested modeling system that combines long- and short-range impacts (referred to as TRACK-ADMS [Trajectory Model with Atmospheric Chemical Kinetics–Atmospheric Dispersion Modelling System]), and the Fine Resolution Atmospheric Multi-pollutant Exchange (FRAME) model. An evaluation of the baseline calculations against U.K. monitoring network data is performed. The CMAQ modeling system version 4.6 data set is selected as the reference data set for the model footprint comparison. The annual mean air concentration and total deposition footprints are summarized for each modeling system. The footprints of the power station emissions can account for a significant fraction of the local impacts for some species (e.g., more than 50% for SO2 air concentration and non-sea-salt sulfur deposition close to the source) for 2003. The spatial correlation and the coefficient of variation of the root mean square error (CVRMSE) are calculated between each model footprint and that calculated by the CMAQ modeling system version 4.6. The correlation coefficient quantifies model agreement in terms of spatial patterns, and the CVRMSE measures the magnitude of the difference between model footprints. Possible reasons for the differences between model results are discussed. Finally, implications and recommendations for the regulatory assessment of the impact of major industrial sources using regional air quality modeling systems are discussed in the light of results from this case study. IMPLICATIONS Modeling tools are required to assess the contribution of industrial sources to ambient levels of air pollution, acid deposition, and eutrophication. This study evaluates the performance characteristics of regional air quality modeling systems in predicting contributions of the emissions from a U.K. regulated fossil-fuel power station to regional air pollution and deposition. It contrasts acid deposition modeling approaches used in the United Kingdom and demonstrates the sensitivity of the modeling systems to large emission changes. This work suggests considering an ensemble average of model calculations to provide an estimate of the uncertainty associated with an industrial source footprint.

Quantifying missing annual emission sources of heavy metals in the United Kingdom with an atmospheric transport model.

An atmospheric chemical transport model was adapted to simulate the concentration and deposition of heavy metals (arsenic, cadmium, chromium, copper, lead, nickel, selenium, vanadium, and zinc) in the United Kingdom. The model showed that wet deposition was the most important process for the transfer of metals from the atmosphere to the land surface. The model achieved a good correlation with annually averaged measurements of metal concentrations in air. The correlation with measurements of wet deposition was less strong due to the complexity of the atmospheric processes involved in the washout of particulate matter which were not fully captured by the model. The measured wet deposition and air concentration of heavy metals were significantly underestimated by the model for all metals (except vanadium) by factors between 2 and 10. These results suggest major missing sources of annual heavy metal emissions which are currently not included in the official inventory. Primary emissions were able to account for only 9%, 21%, 29%, 21%, 36%, 7% and 23% of the measured concentrations for As, Cd, Cr, Cu, Ni, Pb and Zn. A likely additional contribution to atmospheric heavy metal concentrations is the wind driven re-suspension of surface dust still present in the environment from the legacy of much higher historic emissions. Inclusion of two independent estimates of emissions from re-suspension in the model was found to give an improved agreement with measurements. However, an accurate estimate of the magnitude of re-suspended emissions is restricted by the lack of measurements of metal concentrations in the re-suspended surface dust layer.

Modelling emission, concentration and deposition of sodium for Poland

The aim of this paper was to calculate natural and anthropogenic emission of Na + and to estimate, with the FRAME model, annual air concentration and deposition of Na + for the domain covering Poland. Calculations of natural emissions included marine emission and wind blown dust from land. Anthropogenic emission was calculated for both point and area sources. Emission maps were used in fine resolution atmospheric multi-pollutant exchange (FRAME) model, and annual average concentration and total deposition of Na + at the 5 km × 5 km spatial resolution were calculated. A clear gradient from the north and north west towards the centre of Poland is observed for spatial distribution of air concentration and wet deposition of Na + , as sea salt aerosol contributes the majority of Na + deposited in Poland. Comparison of FRAME wet deposition results with available measurements values indicates that the model is capable of reproducing annual deposition of sodium in Poland.

Regional scale modelling of the concentration and deposition of oxidised and reduced nitrogen in the UK

The Fine Resolution Atmospheric Multi-pollutant Exchange model (FRAME) was applied to model the spatial distribution of air concentration and deposition of nitrogen (N) compounds between 1990 and 2005. Modelled wet deposition of N was found to decrease more slowly than the emissions reductions rate. This is attributed to a number of factors including increases in NOx emissions from international shipping and changing rates of atmospheric oxidation. The modelled deposition of NOy and NHx to the United Kingdom (UK) was estimated to fall by 52 % and 25 % between 1970 and 2020. The percentage of the UK surface area for which critical loads for sensitive ecosystems are exceeded was estimated to fall from 73–49 % for nutrient N deposition. Comparison with model simulations at 1 km and 5 km resolution demonstrated that fine scale simulations are important in order to spatially separate agricultural source regions from sink areas (nature reserves) for ammonia dry deposition.

Modelling the Concentration and Deposition of Heavy Metals in the UK

A relatively simple Lagrangian atmospheric transport model (FRAME) was adapted to simulate the concentration and deposition of nine heavy metals (As, Cd, Cr, Cu, Pb, Ni, Se, V and Zn) in the UK. The modelled data was compared with annually averaged measured wet deposition of metals and concentrations in air. The model obtained good correlation with measurements of metal concentrations in air but with very large underestimates (normalised mean biases in the range −0.64 to −0.93), indicating a major under-estimate in total atmospheric emissions. Wet deposition was less closely correlated to measurements. Inclusion of estimates of spatial re-suspension of wind-driven dust for the UK in the model simulation led to an improvement in agreement with measured concentrations. However the amount of re-suspended material was considered to be highly uncertain due to the limited availability of measurement data of the heavy metal content of surface soil and dust.

Modelling the Emission, Air Concentration and Deposition of Heavy Metals in Poland

The aim of this paper was to calculate emission, air concentration and deposition of cadmium (Cd), and lead (Pb) for Poland with the Fine Resolution Atmospheric Multi-pollutant Exchange model (FRAME). Calculations of anthropogenic sources of heavy metals (HM) were based onPM10 emissionsand coefficients of activity and emission, dependent on SNAP sector and type of fuel. Natural emissions were estimated using PM10 wind blown dust from the Nat Air project and HM concentration in topsoil, taken from the Geochemical Atlas of Europe. Emission maps were used in the FRAME model, and annual average concentration and total deposition of individual HM were calculated at a 5 km × 5 km spatial resolution. It was found that the regions with the highest values of HM concentration and deposition were Upper Silesia (industrial region), as also legally protected areas of National Parks.

Nitrogen deposition in the UK: The influence of grid-space and time on the exceedance of critical loads and levels

Atmospheric transport models may be applied to run historic emissions scenarios, which are important in order to assess the correlation between monitored change in ecosystem health and biodiversity and changes in nitrogen inputs. The ability of models to calculate the response of nitrogen deposition to future emissions scenarios is of importance for policy makers to assess the benefits of implementing controls on atmospheric nitrogen emissions. Here we apply a relatively simple Lagrangian model, the Fine Resolution Atmospheric Multi-pollutant Exchange (FRAME) model to estimate the spatial distribution of nitrogen deposition in the UK, past and estimated future changes and the exceedance of critical loads. A second important issue concerns the grid resolution of the model simulation. We consider the difference in environmental impact criteria obtained with model simulations at 5 km and 1 km.