NO x and NO 2 concentrations, trends and sources

Transcription

1 NO x and NO 2 concentrations, trends and sources David Carslaw London Air Quality Network Seminar 11 1st July 11

2 Outline 1 Trends in ambient measurements of NO x and NO 2 2 Vehicle emissions of NO x and NO 2 3 Concluding remarks David Carslaw Environmental Research Group King s College London 2

3 1 Trends in ambient measurements of NO x and NO 2 How have NO x and NO 2 concentrations changed in the UK over the past decade or so? How do these trends compare with Europe? Estimated trends in primary NO 2 emissions derived from ambient measurements What conclusions can be drawn from this information? David Carslaw Environmental Research Group King s College London 3

4 NO x trends across the UK NO X (µg m 3 ) Inner London roadside Outer London roadside London urban background 1 UK roadside motorway UK rural/remote Similar patterns observed at most site types levelling off of NO x concentrations Reduction in concentration from late 199s; weakly decreasing since 2/4 1 2 UK urban background 1 1 UK urban centre 1 Median changes 2 9: %/year in inner London 1.7 %/year in outer London year 1.4 %/year in rest of UK David Carslaw Environmental Research Group King s College London 4

5 NO 2 trends across the UK Inner London roadside London urban background motorway Outer London roadside 3 UK roadside 3 UK rural/remote NO 2 concentrations have increased at some sites NO 2 (µg m 3 ) 7 3 UK urban background 8 7 UK urban centre Median changes 2 9:.5 %/year in inner London.8 %/year in outer London %/year in rest of UK year David Carslaw Environmental Research Group King s College London 5

6 How does the UK compare with the rest of Europe? 8 1 Europe UK Percent of Total Rural Suburban Urban Background Europe Europe Rural Suburban Urban Background UK UK Analysis of hourly data from 2,728 sites in Europe from Airbase Similar proportion of sites in 8 exceed annual mean LV of µg m Industrial Roadside Europe Europe Industrial Roadside UK UK Also evidence of stabilising concentrations of NO 2 for most countries NO 2 (µg m 3 ) David Carslaw Environmental Research Group King s College London 6

7 Austria Belgium Czech Republic Denmark 8 France Germany Greece Italy NO 2 (µg m 3 ) 8 Netherlands Norway Sweden Switzerland year David Carslaw Environmental Research Group King s College London 7

8 Primary NO 2 trends London f NO 2 (% by Vol.) year The ratio of NO 2 :NO x has clearly increased over the past decade Values today in London are around 25% by vol. Higher in London than the rest of the UK on average David Carslaw Environmental Research Group King s College London 8

9 2 Vehicle emissions of NO x and NO 2 What we expected to happen Recent evidence from vehicle emission remote sensing A closer look at diesel cars David Carslaw Environmental Research Group King s College London 9

10 Vehicle emissions legislation in Europe PM (g km 1 ) Euro 6 Euro 5 Euro 1 Euro 2 Euro 3 Euro NO X (g km 1 ) Approximate limits of NO x and PM for diesel cars order of magnitude reduction in NO x g km 1 emissions since early 199s Expect considerable effect on ambient concentrations of NO x and NO 2 David Carslaw Environmental Research Group King s College London 1

11 Vehicle emissions legislation test cycles speed (km hr 1 ) NO X (g km 1 ) time (s) EuroClass variable Limit Measured Vehicles driven over a standard test cycle and emissions measured and expressed in g km 1 Each new model car produced by a manufacturer is tested in this way Thousands of vehicles diesel cars in this case David Carslaw Environmental Research Group King s College London 11

12 Vehicle emissions remote sensing Remote sensing Infrared/UV beam across road using ESP Remote Sensing Detector (RSD-4) Individual vehicle exhausts measured Camera Vehicle Detector (Number plate) (Speed andacceleration) Source/Detector Emissions Analyser (Common Configurations) Mirror Box Source Detector Measures ratios of NO, CO, HC, smoke to CO 2 i.e fuel-based emission factors Some practical limitations Several campaigns from 8 1 in 5 urban areas About 72, vehicles sampled Number plates matched by CarweB ( David Carslaw Environmental Research Group King s College London 12

13 NO x /CO 2 ratio by year NO X/CO2 vol. ratio * CAR LGV year manufactured HGV BUS FuelType DIESEL PETROL NO x emissions from petrol cars have decreased by 96% since the early 199s Diesel car emissions have increased, or at best been stable for the past 25 years or so Possible to see the effects of different Euro class legislation David Carslaw Environmental Research Group King s College London 13

14 Derived vehicle emission factors for NO x (g km 1 ) petrol car diesel car diesel LGVs NO X (g km 1 ) Euro Euro 1 Euro 2 Euro 3 rigid HGV Euro 4 Euro 5 Euro Euro Euro 1 Euro 2 Euro 3 urban bus Euro 4 Euro 5 Euro Euro Euro 1 Euro 2 Euro 3 Euro 4 Euro 5 Euro 6 Some important differences between the different emission factors Reveals important areas of disagreement Euro Euro I Euro II Euro III Euro IV Euro V Euro VI Euro Euro I Euro II Euro III Euro IV Euro classification Euro V Euro VI Emission.factors current UK factors HBEFA (1) remote sensing data David Carslaw Environmental Research Group King s College London 14

15 Vehicle specific power as an emissions metric 1 d (E Power VSP = = dt Mass Vehicle Specific Power (VSP) m a F Aerodynamic F rolling m g Kinetic + E Potential ) + F Rolling v + FAerodynamic v + Fint v ernal friction = m v a (1 + εi ) + g grade v + g C 1 A v + ρac D (v + v 2 m 2 ) v + C v R w if Relates to actual forces a vehicle must overcome Vehicle speed alone is not a good indicator of emissions VSP is the basis of the US-EPA emissions calculations for vehicles 1 Jiménez, J., McClintock, P., McRae, G., Nelson, D., Zahniser, M., Vehicle Specific Power: A Useful Parameter for Remote Sensing and Emission Studies. 9th CRC On-Road Vehicle Emissions Workshop San Diego, April 21st 1999 David Carslaw Environmental Research Group King s College London 15

16 Effect of vehicle specific power on emissions of NO x E Levels of NO X/CO 2 by vehicle speed and VSP 1 3 E1 E2 1 Clear effect for diesel cars by emissions technology Vehicle Specific Power (kw/t) E3 1 3 E4 speed (km hr 1 ) E Euro 3 to Euro 5 emit much higher levels of NO x when the engine is under load Diesel cars have got more powerful over time (use of turbo-charging) David Carslaw Environmental Research Group King s College London 16

17 Have we got the fleet right for inventories? proportion DIESEL PETROL year of manufacture FuelType DIESEL PETROL Inventories do not used observed fleets Remote sensing data captures mileage-weighted fleet statistics David Carslaw Environmental Research Group King s College London 17

18 Have we got the fleet right for inventories? percent 3 diesel petrol variable UK.stock RSD Inventories do not used observed fleets Remote sensing data captures mileage-weighted fleet statistics Euro class In other words: more higher emitting petrol cars than we thought (Euro 1/2) and increased use of modern diesel cars which are high NO x and NO 2 emitters David Carslaw Environmental Research Group King s College London 18

19 3 Concluding remarks Trends in NO x and NO 2 have levelled off in the past 6 8 years UK inventories are in clear disagreement with ambient trends The situation in much of the rest of Europe looks similar Vehicle emission remote sensing data is extremely valuable Key has been linking with comprehensive vehicle information databases (CarweB) Can re-calculate NO x emissions and compare with inventories Light duty vehicle emissions seem to account for most of the disagreement David Carslaw Environmental Research Group King s College London 19

20 Increased power of diesel cars over past years is important Future trends in NO 2 Turn over in vehicle stock will be important e.g. number of older petrol cars on the road The emissions performance of Euro 6/VI is of critical importance and evidence of real-world performance is key David Carslaw Environmental Research Group King s College London

21 Draft report available at and revised version with Defra Covers far more information than presented here along with implications for measures and policy development David Carslaw Environmental Research Group King s College London 21

22 Acknowledgements This work has relied on significant input from others: Sean Beevers, Emily Westmoreland and Martin Williams (ERG, King s College London) James Tate (ITS, University of Leeds) Tim Murrells, Yvonne Li, John Stedman and Andrew Kent (AEA) Enviro Technology Services plc (for provision of some of the remote sensing data) David Carslaw Environmental Research Group King s College London 22

23 Thank you for your attention!!