Polyarom atic hydrocarbons ( PAHs) John W atterson ( w ith thanks to Peter Colem an, Chris Conolly, Mike W oodfield, Chris Dore and Geoff Dollard) W hat’s in this presentation • What are PAHs • EU Directive • UK position • Important sources of PAHs in the UK • Atmospheric fate and transport • Health effects of PAHs • Measurements networks and current concentrations in air • Data in the NAEI and NAQIA 1
W hat are PAHs? • They are polyaromatic hydrocarbons • Polyaromatic hydrocarbons consist of – two or more fused benzene rings – in linear, cluster or angular arrangements • … and contain only carbon and hydrogen • Why worry about them? W hy w orry about PAHs? • Ubiquitous, as – formed during combustion of fossil fuels • Some are probable or possible human carcinogens – International Agency for Research on Cancer (IARC) Group 2A: The agent (mixture) is probably carcinogenic to humans , e.g. – Benzo[ a] pyrene (BaP), Benz[ a] anthracene 2
Groupings and classifications - w hich PAHs should w e m easure? • There are lots of PAHs! • There is no internationally recognised suite of PAHs to assess in air – List frequently encountered is US ‘EPA 16’ – In some international fora, the ‘Borneff 6’ is used – Within the UNECE POPs protocol the four least volatile of the ‘Borneff 6’ compounds are reported Som e im portant PAHs - physical and chem ical properties • Benzo[ a] pyrene ( BaP) Benzo[ def] chrysene 3,4-Benzopyrene 6,7-Benzopyrene 1,2-Benzpyrene 4,5-Benzpyrene • Molecular form ula: C 20 H 12 • CAS Registry No.: 50-32-8 • Boiling point ° C: 496 • Melting point ° C: 178.1 • Vapour Pressure ( Pa at 2 5 ° C) 7.0 x 10 -7 [ 1] 3
EU policy fram ew ork ( this drives UK policy ) • Air Quality Framework Directive 96/ 62/ EC, which now has several Daughter Directives – lists pollutants for which limit values are to be set – sets out framework to manage AQ • assessment of AQ • monitoring methods and networks • plans and programmes to improve AQ • reporting to Commission • informing the public of current AQ Daughter directives • 1999/ 30/ EC – NO x , SO 2 , Particulate Matter (PM 10 ), lead • 2000/ 69/ EC – CO and benzene • 3rd Daughter Directive – ozone 4
4 th Daughter Directive • 4th Daughter Directive – proposal under preparation – arsenic, cadmium, nickel, mercury (possibly) – and PAH – BaP going to be used as a marker – metals and PAH to be in separate directives ??? Not finally decided yet Lim it values currently being proposed in 4 th Daughter Directive • BaP 1 ng/ m³ excess risk 1: 10 -4 (possible threshold) excess risk 1: 10 -5 • As 6 ng/ m³ (possible threshold) excess risk 1: 10 -5 • Cd 5 ng/ m³ (confounding by As) • Ni 20 ng/ m³ excess risk 1: 10 -5 (speciation ) • Hg 50 ng/ m³ not going to be proposed Note: lifetime excess risks 5
Excess Risk - w hat does this m ean and how is it used? • In this case, Excess Risk of lung cancer • WHO guidance suggests that the unit risk of lung cancer is 87 x 10 -6 per ng BaP per m 3 for lifetime exposure • In plain English, this means there is a 87 in a million chance of dying from lung cancer over a lifetime, from exposure to 1 ng per m 3 of BaP throughout your life Excess Risk - how m uch risk is acceptable ? • WHO has considered health based evidence • View that the upper limit of the additional lifetime risk should be less than 1 x 10 -4 • ~ 1 x10 - 6 per year is generally accepted as the maximal risk level • The WHO uses 70 years as an average lifetime ... • … and so the maximum acceptable risk over a lifetime is 70 x ~ 1 x 10 -6 = ~ 70 x 10 -6 6
Now w e can calculate the acceptable am bient concentration ~ 7 0 x 1 0 -6 ( m axim um acceptable risk over a lifetim e) = ~ 1 ng per m 3 8 7 x 10 -6 ( unit risk of lung cancer from BaP over a lifetim e) • Member States have variously set guideline or mandatory values of between 0.1 and 1.3 ng BaP/ m 3 • Since the risk has been evaluated on a lifetime exposure basis these limits usually relate to a yearly average • Suggests a common air quality standard for BaP of less than 1.0 ng/ m 3 , averaged over a yearly period Risk and the public - Com parative risks 7
Other relevant EU legislation • PAHs are covered by the Persistent Organic Pollutant (POP’s) Protocol – under the United Nations Economic Commission for Europe’s Convention on – Long Range Transboundary Air Pollution [ UN ECE CLRTAP] • Under the Protocol, emissions of four PAH compounds have to be reported annually Persistent Organic Pollutant ( POP’s) Protocol • Protocol and emissions in the future ... – PAH in 2010 may not exceed the levels of 1990 (or any other base year between 1985 and 1995) • The Protocol will enter into force after 16 ratifications – which is expected between 2001 and 2002 8
Persistent Organic Pollutant ( POP’s) Protocol • The European Community is a party to the Convention • Will therefore have to fulfil the obligations of the Protocol after ratification • (Including the UK!) European m em ber states am bient air PAH standards • Of EU member states currently only Italy has legally enforceable ambient air standards for PAH • Five others have issued guidance for planning and policy purposes • All have used BaP as a marker for PAH • Sweden has gone further and set a value for fluoranthene as well. 9
Other EU legislation indirectly affecting PAH concentrations • Other Directives indirectly influence PAH emission or concentration in ambient air – arising from the Auto Oil programme – on the incineration of wastes - the IPPC directive (96/ 61/ EC) – the air quality framework directive (96/ 62/ EC) – and its first daughter directive - 1999/ 30/ EC which addresses particulate matter Daughter Directive 1 9 9 9/ 3 0/ EC • The objectives of 1999/ 30/ EC can not be met – without the control of the emissions of particulate material from a very wide range of sources – many of which are sources of PAH as well 10
Vehicle em issions and W HO lim its • New vehicle emissions regulation ('EURO IV') will, in time, further reduce particulate emissions and also PAH • The World Health Organisation [ WHO] has examined the issue of PAH health risk on a number of occasions – published Air Quality Guidelines in 1987 and 2001 UK position on PAHs • The UK government continues to set standards for pollutants in ambient air in order to protect human health • Recently, UK Expert Panel on Air Quality Standards (EPAQS) (1999) issued a draft report 11
UK position on PAHs • EPAQS recommending that an annual average concentration for benzo[ a] pyrene (BaP) in air as – 0.25 ng m -3 – would make the risk to human health from inhalation of PAHs insignificant • The EPAQS approach assumes that BaP is a marker for the health effects of PAHs Sources of PAHs in the UK • There are five major emission source components – Domestic – Mobile – Industrial – Agricultural – Natural • Relative importance of these sources is expected to change with time as a result of regulations and economic development 12
UK em issions of BaP ( kTonnes) from a range of sources 90 80 70 Other 60 Nature (Fires) 50 Agriculture Road Transport 40 Production Processes 30 Residential Combustion 20 10 0 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 I ndustrial sources • Most important industrial sources include – cokeries – primary aluminium production (in particular plants using the Soderberg process) – and wood preservation • Industrial sources are being increasingly regulated (e.g. through I PPC); in addition improved energy management is leading to reduced/ improved combustion 13
I ndustrial sources • Total PAH emissions from industrial sources are decreasing due to regulation (I PPC) • BaP from industrial sources is largely associated with particles < 2.5 µm • Some industrial sources have considerable impact on local air quality, even after applying BAT Dom estic sources • Emissions are predominantly associated with the combustion of solid fuels (as wood and coal) • BaP from domestic sources is associated with a range of particle size including < 2.5 µm • Sources are numerous and widespread • There is no uniform European regulation • Improvements can be achieved using new combustion appliances and fuel switching 14
A day in a city in the 1 9 5 0 s ... SO 2 but also PAHs Unpredicted sources of PAH - Pyres from the foot and crisis 15
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