Air quality expert group - Fine particulate matter (PM2.5) in ... - Defra

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Table 5.5: Population-weighted mean contributions to annual mean PM2.5 in Great Britain in 2010 and projections to 2020 from the UKIAM model (µg m -3 ). The % reductions between 2010 and 2020 are also shown. Component 2010 2020 Primary PM2.5 1.23 0.82 (33%) SIA (SO 2- - + NO + NH4 +) as PM2.5 4 3 – from UK emissions 2.30 1.61 – from shipping (within 200 nautical miles) 1 0.80 0.61 – other, including imported from Europe 1.65 0.95 Other components Total 4.75 3.17 (33%) – soil and other dust particles 2 1.01 same – sea salt 2 0.66 as – secondary organic aerosol (SOA) 3 0.65 2010 – water (based on EMEP model) 1.37 Total 3.69 3.69 (0%) TOTAL 9.67 7.63 (21%) 1 Shipping emissions from AMEC/ENTEC excludes reductions under MARPOL in 2010 but reductions under MARPOL are in effect by 2020. 2 UKIAM makes use of results from the PCM model for these components. 3 Based on the HARM/ELMO model (Whyatt et al., 2007). 5.7 Conclusions and recommendations Modelling PM2.5 and the future 51. Models have important roles to play in understanding PM2.5. These include assessing concentrations at locations without monitors and answering questions such as how will PM levels change in the future, what are the most important emission sources to control to reach acceptable air quality and what balance should be struck between policy actions within the UK and abroad. However, modelling of PM2.5 remains a substantial challenge because of uncertainties in the measurement data, uncertainties/lack of understanding of some aspects of the dynamic, physical and chemical processes which need to be described within the models, and uncertainties in the emission data and their projections. 52. A wide range of PM models covering all scales from the urban to the regional are used to predict UK air quality. The models are based on a range of modelling systems (e.g. Eulerian, Lagrangian and Gaussian plume). Models are useful for aggregating the different contributions to PM, for example to rural background PM from: vehicular and stationary sources; short- and long-range formation and transport from the UK PM precursor sources; long-range transboundary formation and transport of primary and secondary PM; and intercontinentalscale PM formation and transport. 143
PM2.5 in the UK 144 53. Modelling results have illustrated how primary PM2.5 concentrations show localised peaks in urban areas owing to local sources, superimposed on a regional background. The sources which cause these peaks are potentially subject to abatement and the dispersion of these sources are generally well represented by models, except when close to roads with complex street geometries. An important limiting factor in estimating concentrations and human exposure is likely to be uncertainty in the emissions, including missing sources. 54. The largest contribution to PM2.5 concentrations overall is secondary inorganic aerosol (SIA). Secondary inorganic aerosol contributions are more smoothly varying, resulting from advection on a range of scales up to continental and illustrated by higher average concentrations in the south-east graduating to much lower values over Scotland. Nitrate is the largest component of SIA over the UK, and also the most spatially variable in space and time, depending as it does on the variability of ammonia emissions and concentrations. More detailed research is required to investigate the effect of temporal variations in emissions, especially of ammonia, and explain the seasonal variation and the higher nitrate levels observed in winter. Sulphate now makes a smaller contribution to PM2.5 concentrations than nitrate owing to major reductions in sulphur emissions in the UK and in other countries and from shipping. 55. The ratio of urban increment to regional background points to future directions for PM2.5 control. Control strategies should be considered for the regional background where secondary inorganic aerosol is by far the largest component according to models. It is also worth noting that given the exposure reduction targets outlined in Chapter 1, the removal of the whole of the urban increment would be required to satisfy them if nothing is done to address the regional background. 56. Source apportionment from modelling shows how further reductions in SIA depend on the control of emissions of SO2, NOx and NH3 in other countries, and from shipping more generally, as well as in the UK. Scenario analysis shows dependence on future emission ceilings in the EU-27 countries and also the modelled reduction of sulphate resulting from the MARPOL agreement of the International Maritime Organization (IMO), counteracted by enhanced nitrate due to increasing shipping emissions of NOx. Modelling indicates a complex non-linear response of SIA concentrations to reductions in precursor emissions due to chemical interactions between pollutants, in particular the high dependence on the availability of NH3 and the reversible and temperaturedependent formation of ammonium nitrate. This needs to be borne in mind when considering the effectiveness of further SO2 and NOx reductions, whilst emissions of NH3 have remained more constant. 57. Modelling of the smaller secondary organic aerosol (SOA) component is far more uncertain and speculative than for SIA, both in terms of precursor emissions (see Chapter 4) and chemical processes, and further work is required in this area. However, it is more difficult to control SOA and its precursors, of which biogenic emissions are a large component. It is worth noting that the oxidants for biogenic VOC precursors, namely hydroxyl ions (OH - ), ozone (O3) and NO3 - , are all controlled by atmospheric chemistry, and will respond to further reductions in carbon monoxide (CO), SO2, NOx and VOC emissions. It is
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AIR QUALITY EXPERT GROUP Fine Parti
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This is a report from the Air Quali
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II Membership Chair Professor Paul
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IV Acknowledgements The Air Quality
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VI 2.5 Summary 39 2.5.1 What does t
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VIII 5.4 Components of PM2.5 and so
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PM2.5 in the UK 2 Air Quality Direc
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PM2.5 in the UK 4 I.2.1 Concentrati
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PM2.5 in the UK 6 • PM2.5 emissio
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PM2.5 in the UK 8 I.4.1 Modelling r
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PM2.5 in the UK 10 4. In broad term
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PM2.5 in the UK Table 1.2: National
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PM2.5 in the UK 14 17. Dry depositi
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PM2.5 in the UK 16 in ozone in the
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PM2.5 in the UK 18
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PM2.5 in the UK 20 5. The exact for
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PM2.5 in the UK 22 12. These diffic
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PM2.5 in the UK 24 2.3 Methods used
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PM2.5 in the UK 26 (e) During the
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PM2.5 in the UK 28 2.3.3 The Partis
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PM2.5 in the UK 30 35. For non-auto
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PM2.5 in the UK 32 43. Ratification
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PM2.5 in the UK 34 49. Many of the
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PM2.5 in the UK 36 57. Black carbon
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PM2.5 in the UK 38 2.4.4 PM2.5 elem
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PM2.5 in the UK 40 average of 93.6%
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PM2.5 in the UK Annex 1 - PM2.5 mon
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PM2.5 in the UK 44
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PM2.5 in the UK 46 3.2.1 Diurnal va
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PM2.5 in the UK 48 PM2.5/µgm -3 20
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PM2.5 in the UK 50 3.2.4 Seasonal v
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PM2.5 in the UK 52 12. Results are
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PM2.5 in the UK 54 3.4.2 Relationsh
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PM2.5 in the UK 56 Correlation 0.8
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PM2.5 in the UK Figure 3.11: Polar
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PM2.5 in the UK 60 south. Further a
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PM2.5 in the UK 62 3.7 PM2.5 episod
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PM2.5 in the UK 64 secondary ammoni
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PM2.5 in the UK 66 3.8 PM2.5 concen
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PM2.5 in the UK 68 3.9 Composition
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PM2.5 in the UK 70 43. The UK has i
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PM2.5 in the UK 72 NO 3 6 4 2 2000
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PM2.5 in the UK 74 54. PM ammonium
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PM2.5 in the UK 76 58. Data from th
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PM2.5 in the UK 78 (k) Road traffic
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PM2.5 in the UK 80 provided by spec
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PM2.5 in the UK 82 14. The London L
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PM2.5 in the UK Table 4.1: UK emiss
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PM2.5 in the UK 86 24. National inv
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PM2.5 in the UK 88 Figure 4.5: Spat
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PM2.5 in the UK 90 either nanoparti
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Page 131 and 132: PM2.5 in the UK 120 105. Receptor m
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Page 139 and 140: PM2.5 in the UK 128 Figure 5.2: Tot
Page 141 and 142: PM2.5 in the UK 130 µgm -3 160 140
Page 143 and 144: PM2.5 in the UK 132 PM component (
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Page 147 and 148: PM2.5 in the UK 136 Figure 5.8: UKI
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Page 153: PM2.5 in the UK 142 the North Sea (
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Page 159 and 160: PM2.5 in the UK 148 2. Figure A2.1.
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Page 165 and 166: PM2.5 in the UK 154 (a) (b) modPM 2
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Page 171 and 172: PM2.5 in the UK 160 SIA components
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Page 175 and 176: PM2.5 in the UK 164 A2.6: Photochem
Page 177 and 178: PM2.5 in the UK 166 PM2.5 Emission
Page 179 and 180: PM2.5 in the UK 168 A2.8: PCM PM mo
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