The quality of the air we breathe Mike Pilling School of Chemistry, University of Leeds UK Air Quality Strategy, 2007 “Air pollution is currently estimated to reduce the life expectancy of every person in the UK by an average of 7-8 months. The measures outlined in the strategy could help to reduce the impact on average life expectancy to five months by 2020, and provide a significant step forward in protecting our environment.” Defra estimate the health impact of air pollution in 2005 cost £9.1–21.4 billion pa. Synopsis 1. Particulate matter: trends and origins. 2. NO2: increases in emissions of primary NO2 and its impact on roadside and kerbside concentrations 3. Ozone 4. Air quality and climate change Particulate matter PM • categorised on the basis of the size of the particles (e.g. PM2.5 is particles with a diameter of less than 2.5μm). •comprises wide range of materials (soot, nitrate, sulphate, organic compounds) •primary particles emitted directly into the atmosphere from combustion sources •secondary particles formed by chemical reactions in the air. •derives from both human-made and natural sources (such as sea spray and Saharan dust) •health effects: inhaled into the thoracic region of the respiratory tract. associated with respiratory and cardiovascular illness Particulate matter: trends in emissions and measured concentrations (UK) 180 160 Black smoke, Lambeth, 1961 - 1997 Black smoke , ug/m3 140 600 500 120 100 80 60 20 400 0 1997 1995 1993 1991 1989 1987 1985 1983 1981 1979 1977 1975 1973 1971 1969 1967 1965 300 1963 1961 40 200 35 100 30 Belfast Centre Birmingham Centre 0 Bristol Centre 1970 1975 Public Power Production Processes Resuspension 1980 1985 1990 Comm.Res.&Instit. Comb. Road Transport 1995 2000 Industrial Combustion Other PM10 TEOM , ug/m3 25 Cardiff Centre London Bloomsbury Edinburgh Centre 20 Leeds Centre Leicester Centre Liverpool Centre Newcastle Centre 15 Southampton Centre Swansea Primary PM10 emissions sources 1970 – 2001 (AQEG: PM report) Average 10 Annual mean PM10, Urban Background sites 5 AQEG PM report 2003 2002 2001 2000 1999 1998 1997 1996 1995 1994 1993 0 1992 PM 10 emissions (kt) 40 Air quality – comparison of trends in pollutants relative annual mean concentration 120 100 80 60 40 SO2 PM10 CO NOx NO2 20 0 1997 1998 1999 2000 2001 Year 2002 2003 2004 Relative annual mean concentration (monthly intervals): selection of monitoring sites in London. AQEG PM report Analysis of data from 196 sites in UK in 2003 Annual Average PM10 Concentrations for 2003 (ugm TEOM) at Roadside, Urban and Rural Sites -3 40 Annual PM10 TEOM Average Annual PM10 TEOM 35 High rural background PM10 ugm -3 TEOM 30 25 20 15 10 5 Small number of rural sites 0 AQEG PM report Roadside, urban background and rural annual average PM10 TEOM concentrations in 2003 Secondary PM • PM is also formed as a secondary pollutant by chemical reactions in the atmosphere. • This includes oxidation reactions leading to the formation of secondary PM containing: • Sulphate • Nitrate • Organic compounds • The chemistry involved is close to that involved in ozone formation and explains why ozone episodes are accompanied by enhanced PM PM episodes – other sources Saharan dust: e.g. 2-3 March 2002. Hourly mean of 292 g m-3 at Plymouth. 1-2 events per year in UK. 23 in Spain! Sea salt aerosol during gales, especially coastal sites but also inland. 1-5 episodes / year. Biomass burning: Forest fires in Russia, September 2002. Peak hourly concentrations in were reported on the 12th of September in the range from 70 – 125 g m-3. AQEG PM report Biomass plumes, W Russia, 4 September 2002 Air Quality Strategy 2007 - PM Dual approach: air quality objective/limit value (backstop objective): PM2.5: annual mean 25μg m-3 by 2020 Exposure reduction: an objective based on reducing average exposures across the most heavily populated areas of the country: 15 per cent reduction in average concentrations in urban background areas across the UK between 2010 and 2020 NO2; NOx = NO + NO2 All combustion processes in air produce oxides of nitrogen (NOX). Road transport is the main source, followed by the electricity supply industry and other industrial and commercial sectors. NO2 is associated with adverse effects on human health: causes inflammation of the airways. Long term exposure may affect lung function and respiratory symptoms. Also enhances the response to allergens in sensitive individuals. NO2: EU Limit values Hourly mean: 200 g m-3, not to be exceeded more than 18 times a year, to be achieved by 31st December 2010. Annual mean: 40 g m-3, to be achieved by 31st December 2010. Spatial distribution of NOx emissions in the UK Maps of annual mean background NO2 concentrations UK 2001 UK 2010 Key AQ objective is annual mean of 40 g m-3 to be achieved by 2010 (EU Directive) Air quality – comparison of trends in pollutants relative annual mean concentration 120 100 80 60 40 SO2 PM10 CO NOx NO2 20 0 1997 1998 1999 2000 2001 Year 2002 2003 2004 Relative annual mean concentration (monthly intervals): selection of monitoring sites in London. AQEG PM report NOx and NO2 emissions in London Trends in annual mean NOx and NO2, roadside and kerbside, 1996 - 2005 Lo ndo n M arylebo ne Ro ad B ury Ro adside Glasgo w Kerbside Oxfo rd Centre Ro adside Lo ndo n M arylebo ne Ro ad B ury Ro adside Glasgo w Kerbside Oxfo rd Centre Ro adside NOx, NO2 concentrations Full lines NOx. Dashed lines NO2 450 Concentration (µg m-3, as NO2) 400 350 300 250 200 London Marylebone Road Bury Roadside Glasgow Kerbside Oxford Centre Roadside 0.45 150 0.4 100 0.35 0 1998 1999 2000 2001 2002 2003 2004 2005 Year • NOx shows downward trend, compatible with improved emissions reduction technologies • This trend is not reflected in NO2. • Measured NO2 / NOx ratio generally increases with time. • Not always the case – e.g. Glasgow Ambient NO2/NOx ratio 50 0.3 0.25 0.2 0.15 0.1 0.05 0 1998 1999 2000 2001 2002 Year Ratio NO2 / NOx 2003 2004 2005 Measured [NO2] / [NO] at a number of sites in London Roadside and kerbside LAQN data A30 BN1 1.2 BY7 CD1 NO2/NOx ratio relative to year 2006 = 1 1.1 CR2 CR4 CY1 1 EA2 EN2 0.9 GR5 HF1 HI1 0.8 HS1 HS4 HV1 0.7 HV3 KC2 0.6 MY1 RB3 RB4 0.5 SK2 TH2 WA4 0.4 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 HG1 All sites Estimates of f(NO2) based on atmospheric concentrations of NO and NO2 30 Marylebone Rd f-NO2 20 10 1998 1999 2000 2001 2002 2003 2004 2005 year 30 2006 2007 All London sites 25 20 estimated f-NO2 0 1997 15 10 5 0 1997 1998 1999 2000 2001 year 2002 2003 2004 2005 Similar behaviour across Europe - Paris 700 600 100 500 80 400 60 300 40 NO2 FR0895A Roadside 200 NO2 FR0335A Roadside NOx FR0895A Roadside 20 0 1995 100 NOx FR0335A Roadside 1996 1997 1998 1999 2000 2001 2002 2003 2004 0 2005 Annual mean concentration NOx (ugm-3, as NO2) Annual mean concentration NO2 (ugm-3) 120 NO2 in Budapest and Hungary in 2005 the percentage of urban major road length predicted to be above 40 g m-3 annual mean NO2 in 2010 for different f-NO2 percentages (shown in brackets). 2004 base year (10 - 15%) 2010 (10 - 15%) 2010 (15 - 23%) 2010 (20 - 30%) 2010 (25 - 38%) 2010 (30 - 45%) London 84% 46% 52% 57% 62% 67% Rest of England 31% 11% 14% 16% 18% 20% Scotland 22% 6% 8% 9% 10% 12% Wales 13% 6% 7% 8% 8% 9% Northern Ireland 8% 0% 1% 1% 2% 3% Total 35% 15% 17% 19% 21% 24% AQEG conclusions on primary NO2 Measured NOx concentrations have declined in line with emission changes but NO2 concentrations have not declined as expected, particularly at the roadside and some sites have shown increases in recent years. Increases in NO2 / NOx ratios could be due to: • increased penetration of Euro-III diesel vehicles fitted with oxidation catalysts • Fitting of catalytically regenerative particle traps to buses Exact interpretation difficult given the observation of increases in the NO2/NOx concentration ratio at only some roadside and kerbside sites outside London. Is London particularly sensitive to direct NO2 emissions, because of its size and emission density? But what about Glasgow? NB more analysis carried out for the sites in London because of the greater availability of data in London. Similar increases in NO2 / NOx observed in other European countries. Ozone not emitted directly from any human-made source. Arises from chemical reactions between various air pollutants, NOX and Volatile Organic Compounds (VOCs), initiated by strong sunlight. formation can take place over several hours or days and may have arisen from emissions many hundreds, or even thousands of kilometres away. can damage airways leading to inflammatory reactions; reduces lung function and increases incidence of respiratory symptoms causes damage to many plant species leading to loss of yield and quality of crops, damage to forests and impacts on biodiversity. Air Quality Standards: Ozone European Union Limit Value: Target of 120μg.m-3 (60 ppb) for an 8 hour mean, not to be exceeded more than 25 times a year averaged over3 years. To be achieved by 31 December 2010. UK Air Quality Objective: Target of 100μg.m-3 (50 ppb) for an 8 hour mean, not to be exceeded more than 10 times a year. To be achieved by 31 December 2005. Methane oxidation CH4 + OH (+O2) CH3O2 + H2O CH3O2 + NO CH3O + NO2 CH3O + O2 HO2 + HCHO HO2 + NO OH + NO2 HCHO + OH (+O2) HCHO + hn HO2 + CO + H2O H2 + CO HCHO + hn (+2O2) 2HO2 + CO Note: 2 x(NO NO2) conversions HCHO formation provides a route to radical formation. General oxidation scheme for VOCs O3 + hn O1D + O2 O1D + H2O 2OH OH + RH (+O2) RO2 + H2O RO2 + NO NO2 + RO RO HO2 (+R’CHO) HO2 + NO OH + NO2 NO2 + hn NO + O; O + O2 O3 OVERALL NOx + VOC + sunlight ozone The same reactions can also lead to formation of secondary organic aerosol (SOA) Timescales of ozone chemistry 1. Global chemistry. Dominated by NOx + CH4 + sunlight. Timescales are long as are transport distances. 2. Regional chemistry. • Many VOCs are emitted, e.g. over Europe. Each has its own lifetime governed by its rate constant for reaction with OH. The timescales of ozone production takes from hours to days. The transport distance for a wind speed of 5 m s-1 and a lifetime of 1 day is ~500 km. 3. In cities, there are high concentrations of NO from transport sources. Ozone is depressed by the reaction: NO + O3 NO2 + O2 01/12/2006 01/11/2006 01/10/2006 01/09/2006 01/08/2006 01/07/2006 01/06/2006 01/05/2006 01/04/2006 01/03/2006 01/02/2006 01/01/2006 O3, ug/m3 Sources of ozone in W Ireland 120 100 80 Europe-regional North America 60 Asia Europe-intercontinental 40 Extra-continental Stratosphere 20 0 01/04/2006 01/04/2005 01/04/2004 01/04/2003 01/04/2002 01/04/2001 01/04/2000 01/04/1999 01/04/1998 01/04/1997 01/04/1996 01/04/1995 01/04/1994 01/04/1993 01/04/1992 01/04/1991 01/04/1990 01/04/1989 01/04/1988 01/04/1987 Monthly mean baseline ozone, ug/m3 Ozone mixing ratios at MaceHead W. Ireland, under westerly airflows 110 100 90 80 70 60 50 40 Regional production of ozone in Europe Local effects – Ozone depression due to reaction with high concentrations of NO in London. Transect of ozone concentrations 70 Annual Mean Concentration (in g m-3) 60 50 40 30 20 10 0 465000 475000 485000 495000 505000 515000 525000 535000 545000 555000 Easting PCM 2003 2003 AURN measurements Ascot Rural ADMS-Urban 2003 565000 575000 585000 Heat wave in Europe, August 2003 Monitoring stations in Europe reporting high band concentrations of ozone >15 000 ‘excess deaths’ in France; 2000 in UK, ~30% from air pollution. Temperatures exceeded 350C in SE England. How frequent will such summers be in the future? Future summer temperatures Using a climate model simulation with greenhouse gas emissions that follow an IPCC SRES A2 emissions scenario, Hadley Centre predict that more than half of all European summers are likely to be warmer than that of 2003 by the 2040s, and by the 2060s a 2003-type summer would be unusually cool 2003: hottest on record (1860) Probably hottest since 1500. 15 000 excess deaths in Europe Stott et al. Nature, December 2004 ozone / microg/m3 Budapest, 1 – 31 August 2003 200 180 160 140 120 100 80 60 40 20 0 Széna tér Baross tér Pesthidegkút Kőrakás park Laborc u. 0 100 200 300 400 time 500 600 700 800 Diurnal variation 13th August 2003 Pesthidegkut ozone/ microg/cm3 200 150 100 Ser i es1 50 0 -1 4 9 14 time of day 19 24 Climate change and air quality Global-average radiative forcing (RF) estimates and ranges in 2005 (relative to 1750) for anthropogenic GHGs and other important agents and mechanisms Air Quality and Climate Change UK Air Quality Strategy (2007) The Government’s environmental policies will be developed with a consideration of their impact on climate change and greenhouse gas emissions, and this is particularly true of air quality. Where practicable and sensible, synergistic policies beneficial to both air quality and climate change will be pursued. Where there are antagonisms, the trade-offs will be quantified and optimal approaches will be adopted. Examples of difficult issues in assessing impact of emissions on climate change and air quality • Diesel vehicles: • Need a more complete assessment of savings of CO2 emissions for diesel vs petrol • Difficulties of defining metrics for black carbon emissions (absorptive aerosol) for climate change and in assessing the air quality (health) impacts relative to climate change impacts of CO2 reduction. • Ozone precursors: • NOx emissions impact on global CH4 and O3, both of which are greenhouse gases. Effects are of opposite sign • VOC emissions from biofuel crops could enhance episodic ozone, especially as temperatures rise. Acknowledgement Air Quality Expert Group
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