! ! ! Prepared by M Coyle (CEH Edinburgh). ! ! Transboundary Air Pollution: Acidification, Eutrophication and Ground-Level Ozone in the UK ISBN 1 870393 61 9 For further copies, please contact: Mhairi Coyle Dr. Alison Vipond CEH Edinburgh Air and Environment Quality Division Bush Estate Department for Environment, Food and Rural Affairs Penicuik Ashdown House, Zone 4/D11 Midlothian 123 Victoria Street EH26 0QB London, SW1E 6DE UK UK [email protected] [email protected] tel. ++44(0) 131 445 8528 fax. ++44(0) 131 445 3943 The report is also available in electronic format at http://www.nbu.ac.uk/negtap/. For technical enquires, please contact: Prof. David Fowler CEH Edinburgh Bush Estate Penicuik Midlothian, EH26 0QB UK [email protected] tel. ++44(0) 131 445 4343 fax. ++44(0) 131 445 3943 NEGTAP 2001 Prepared by the National Expert Group on Transboundary Air Pollution (NEGTAP) at CEH Edinburgh on behalf of the UK Department for Environment, Food and Rural Affairs, Scottish Executive, The National Assembly for Wales/Cynulliad Cenedlaethol Cymru, Department of the Environment for Northern Ireland. DEFRA Contract EPG 1/3/153 © NEGTAP 2001 ! ! National Expert Group on Transboundary Air Pollution http://www.nbu.ac.uk/negtap/ D Fowler (Chairman) M Coyle (Secretary) Centre for Ecology and Hydrology Edinburgh H M ApSimon Department of Environmental Science and Technology, Imperial College of Science, Technology and Medicine M R Ashmore University of Bradford S A Bareham Cyngor Cefn Gwlad Cymru/Countryside Council for Wales, Joint Nature Conservancy Committee R W Battarbee University College London R G Derwent Meteorological Office J-W Erisman Energy Research Center of the Netherlands J Goodwin AEA Technology Environment P Grennfelt Swedish Environmental Research Institute M Hornung Centre for Ecology and Hydrology Merlewood J Irwin Environment Agency A Jenkins Centre for Ecology and Hydrology Wallingford S E Metcalfe University of Edinburgh S J Ormerod Cardiff University B Reynolds Centre for Ecology and Hydrology Bangor S Woodin University of Aberdeen Terms of Reference The National Expert Group on Transboundary Air Pollution (NEGTAP) is an advisory, Non- Departmental Public Body. Its work spanned 24 months and the Terms of Reference are: To review current knowledge and advise Ministers on: biological and chemical trends in the UK environment, and the prospects for recovery, as a result of current and projected deposition of transboundary air pollutants UK critical load, and critical load exceedance maps for acidity and eutrophication and advise Ministers on their further development requests from the Government on other transboundary air pollution issues. Information on the Expert Group is available on the internet at http://www.nbu.ac.uk /negtap/, and includes membership, agendas, minutes of meetings, and a register of interests. This report will also be available on the internet at this address. The group will build on the reports from previous groups such as the Review Group on Acid Rain, Photochemical Oxidants Review Group and the Critical Loads Advisory Group. The views expressed in this report are those of the authors and not necessarily those of the organisations they represent or the commissioning bodies. ! ! Executive Summary This report provides a detailed description of the current status of the problems of acid deposition, eutrophication and ground-level ozone pollution in the UK, including emissions, atmospheric concentrations and deposition of the major pollutants, and the impacts on soils, vegetation and freshwaters. A summary of impacts throughout Europe is included to provide a perspective for the assessment. ♦ Emissions of the major pollutants SO2 and NOx in 1999 have declined by 80% and 40% of their respective peak emissions and are projected to decline further by 2010, in line with UK commitments within international protocols. Emissions of NH3 have changed little since the peak emissions in the mid 1980’s, but a decline of 12% relative to 1990 is expected by 2010. ♦ The deposition of sulphur and oxidized nitrogen in the UK has declined since the peak in emissions by 50% for sulphur and 16 % for oxidized nitrogen. However, substantial non- linearities in relationships between emission and deposition have been detected and will continue, so that in some areas of the country the reduction in deposition may continue to be much smaller than the national reduction in emissions. ♦ The acidity of UK rainfall more than halved over large areas of the UK between 1985 and 1999. ♦ Ground-level ozone concentrations regularly exceed the thresholds for effects on vegetation and human health throughout the UK, but the peak concentrations declined by 30% between 1986 and 1999. ♦ The assessment of future pollutant concentrations and deposition rely heavily on numerical models that have improved steadily over the last decade and represent current understanding of the underlying processes, with all their uncertainties. ♦ Reduced inputs of acidity and nitrogen from the atmosphere may provide the conditions in which chemical and biological recovery can begin, but the time scales of these processes are often very long (decades) relative to the time scales of reductions in emission. ♦ Widespread acidification of acid sensitive UK soils occurred through the 20th century and as yet, there is little direct evidence of recovery despite the reduced deposition. ♦ Acidification of freshwaters has been widespread in the uplands of the UK from 1850 onwards. There is clear evidence of chemical change consistent with the beginning of recovery and the first stages of biological recovery have been detected. However, the original species may never become re-established and active site management may be necessary to promote biological recovery. ♦ Critical loads for acidification are currently (1997) exceeded in 71% of UK ecosystems, and this is expected to decline to 47% by 2010 by which time deposited nitrogen will be the major contributor to acidification. ♦ Critical loads for eutrophication are currently (1995-1997) exceeded in ca 25% of UK 1 km x 1 km grid squares with sensitive grasslands and ca 55% with heathland. These percentages are expected to decline to ca 20% and ca 40% respectively in 2010, with reduced nitrogen (NH3 and NH4) being the main contributor. ♦ The reduction in SO2 concentration over the last three decades has virtually eliminated direct effects on vegetation, leading to an expansion of some lichen species. However, current deposition of nitrogen is probably changing species composition in many nutrient-poor habitats and these changes may not be readily reversed. Current O3 concentrations threaten i NEGTAP 2001 ! ! Executive Summary crops and forest production. The effects of ozone and nitrogen deposition are likely to remain significant beyond 2010. ♦ The major ecological problems due to air pollution are common to large areas of Europe where, like the UK, sulphur emissions and deposition have declined substantially and where N deposition has changed relatively little. In continental Europe the deposition of N and the presence of elevated ozone concentrations represent the major ecological problems and while deposition and effects by 2010 will be reduced, widespread exceedances of critical loads and levels will still occur. ♦ The long-term operation of UK networks monitoring the major gaseous, particulate pollutants and those in rain have provided the necessary data, which underpin this assessment. The networks will be vital to demonstrate compliance with international protocols as well as scientific assessment of the state of the UK environment in the future. ii NEGTAP 2001 ! ! Technical Summary This report provides a detailed description of the current status of the problems of acid deposition, eutrophication and ground-level ozone in the UK, covering the emissions, atmospheric concentrations and deposition of the major pollutants and the effects on soils, freshwaters and vegetation. The scope of the report is therefore broad and this short summary identifies the main findings. The subject is presented in order, following the pollutant pathway from source to receptor, which also matches the chapter headings. Emissions (Chapter 2) The UK emissions of most of the pollutants contributing to acid rain, eutrophication and ozone production in (and downwind of) the UK, including sulphur dioxide (SO2), the nitrogen oxides (NOx), carbon monoxide (CO), and non-methane volatile organic compounds (NMVOCs) have declined substantially over the last decade, as detailed below. The exception, ammonia (NH3), shows emissions which have changed little over the last 15 years and are least certain. In the Gothenburg Protocol (to abate acidification, eutrophication and ground-level ozone), the UK agreed annual emission ceilings for SO2 (625 kt-SO2), NOx (1181 kt-NOx), NH3 (297 kt-NH3) and NMVOCs (1200 kt) to be reached from 2010. The proposed EU National Emissions Ceilings Directive will set the emission ceilings for the same four pollutants. During negotiations, the UK has agreed to more stringent ceilings for SO2 and NOx. The emissions are expressed as kt (thousands of tonnes), in the case of sulphur and nitrogen as the elements S and N. ♦ Annual UK emissions of sulphur dioxide peaked in 1970 at 3259 kt-S, declined to 594 kt-S by 1999 and will decline further to around 312 kt-S by 2010. ♦ Annual UK emissions of nitrogen oxides peaked in 1980s at ca 850 kt-N and declined to less than 500 kt-N by 1999. They will continue to decline to around 359 kt-N by 2010. ♦ Annual UK emissions of ammonia are the least certain of all the pollutants that contribute to acidification and eutrophication; they reached approximately 300 kt-N annually in the late 1980s and are expected to decline by 11%, relative to 1990, by 2010. ♦ Annual UK NMVOC emissions peaked in 1989 at 2500 kt, declined to 1700 kt and are set to decline further to 1200 kt by 2010. ♦ Annual CO emissions peaked in 1970s at ca 8500 kt, declined to less than 5000 kt by 1999 and will decline to 2800 kt by 2010.