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A high resolution (5×5 km2) UK-scale chemistry-transport model (EMEP4UK) is used to study ground-level ozone (O3) during the August 2003 heat-wave. Meteorology is generated by the Weather Research and Forecast (WRF) model, nudged every six hours with reanalysis data. We focus on SE England, where hourly average O3 reached up to 140 ppb during the heat-wave. EMEP4UK accurately reproduces observed annual and diurnal cycles of surface O3 at urban and rural sites. Elevated O3 and much of its day-to-day variability during the heat-wave are well captured. Key O3 precursors, nitrogen dioxide and isoprene (C5H8), are less well simulated, but show generally accurate diurnal cycles and concentrations to within a factor of ~2–3 of observations. The modelled surface O3 distribution has an intricate spatio-temporal structure, governed by a combination of meteorology, emissions and photochemistry. A series of sensitivity runs with the model are used to explore the factors that influenced O3 levels during the heat-wave. Various factors appear to be important on different days and at different sites. Ozone imported from outside the model domain, especially the south, is very important on several days during the heat-wave, contributing up to 85 ppb. Dry deposition of O3, when completely switched off, elevated simulated O3 by up to 50 ppb, and this may have been an important factor on several days. Modelled C5H8 concentrations are generally best simulated if C5H8 emissions are changed from the base emissions: typically doubled, but elevated by up to a factor of five on some days. Accurately modelling the exact positions of individual plumes of anthropogenically emitted nitrogen oxides and volatile organic compounds is crucial for the successful simulation of O3 at a particular time and location. Variations in surface temperature of ±5 K were found to have impacts on O3 of typically less than ±10 ppb.

Intercontinental exchange of sulphur in major parts of the northern hemisphere has been studied with a 3-dimensional Eulerian transport model that resolves regional scale variability. Model results for 1988 have been evaluated against daily observations of sulphur dioxide and particulate sulphate in Europe and North America and show that the model reproduces the episodic character of oxidised sulphur in air. Yearly averages agree with the observations within a factor of 2, at over 75% of the sites. Monthly budgets for intercontinental exchange of sulphur are presented and related to large scale atmospheric flow patterns. Intercontinental transport of sulphur is related to mid-latitude cyclone tracks, and few events determine a considerable part of the yearly intercontinental exchange. European anthropogenic sulphur dominates the averaged air concentrations and depositions over the simulation area. The contribution of European sulphur over the Sea of Japan is calculated to be 50–75 mg(S) m −2 yr −1 or 5–10% of the total deposition calculated for that area. Over the West Siberian Planes, the European contribution is estimated to be 150–200 mg(S) m −2 yr −1 that is, 40–50% of the yearly calculated deposition. The relative contributions of intercontinental transport from anthropogenic sources in Asia and North America and biogenic sources in the North Atlantic Ocean to the European deposition levels are similar and range from 2 to 4%. In certain areas and seasons, however, these relative contributions can be much larger. DOI: 10.1034/j.1600-0889.1998.t01-3-00002.x

A 3-dimensional Eulerian model is used to evaluate the influence of North American anthropogenic sulphur emissions over the western coast of Europe. Transport of sulphur across the North Atlantic ocean is simulated on the basis of the actual meteorology for 4 different months during 1982 and 1983. Results show large regional variations and indicate that the relative importance of North American emissions is largest over north western Europe. The North American contribution to pollution levels over western Europe is shown to occur mainly as wet deposition. Maximum wet deposition of North American origin over north western Europe is predicted for January 1983. On average over the four simulated months, the wet deposition of North American origin is estimated to be 2 mg S m -2 month -1 which represents 10% of the calculated total deposition over western Europe. The influence of North American sulphur on the air concentrations over the west coast of Europe is relatively larger at higher levels in the atmosphere. At ground level, the North American contribution to sulphate in air represents only 2.5% of the averaged total calculated, but it ascends to 50% at 5000 m. Maximum contributions to the sulphate concentrations in air over western Europe are estimated to occur during July 1983. DOI: 10.1034/j.1600-0889.1992.t01-1-00004.x