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

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36. The behaviour of semi-volatile constituents is a major problem both for the measurement and modelling of PM2.5. In the case of measurement, the degree of partitioning of semi-volatile compounds into the measured particles is determined by factors such as atmospheric temperature and relative humidity. Consequently, if these change during the sampling interval (as they typically do from day to night), sampling artefacts can occur through the evaporation or condensation of such materials from/on the air filter used in sampling. Additionally, the reduced pressure used to draw air through a sampling filter can encourage the vaporisation of semi-volatile components. The difficulties for modelling start with the prediction of the formation of secondary semivolatile components and continue with the problem of describing their partition into the particles. This is affected by many factors, most notably temperature, relative humidity and the existing composition of the particles, which affect the thermodynamic activities of the soluble components and the uptake into organic films for the hydrophobic components. A further difficulty for modellers is caused by the fact that air sampling methods for PM2.5 are not artefact free and therefore measure concentrations that may not reflect well the true airborne suspended particle mass. 37. Since semi-volatile organic matter and ammonium salts comprise a substantial part of PM2.5 mass, these issues have major implications for both measurement and modelling of concentrations. 5.4.4 Other components 38. In addition to primary PM2.5 from sources represented in the emission inventory and secondary inorganic aerosol, there is a large contribution from other components, many of which are more uncertain and include natural or land use related contributions not subject to control. These include rural dust from wind-suspended soil particles varying with soil characteristics, and urban dust including material resuspended by traffic. Sea salt is another component of natural origin, the influence of which decreases with distance from the coast. 39. Finally, particle bound water makes an additional contribution to particle mass. It might seem that this is another natural component, but it has been argued in legislation concerning PM10 that it is partly associated with man-made SIA contributions. However, estimating any reduction in particle bound water in response to reductions in SO2, NOx and NH3 emissions is extremely uncertain, involving both direct and indirect effects on cloud processes. Hence, in Table 5.5 for example, where water content in UKIAM is based on modelling provided by EMEP, water content is kept constant in future projections (which may be pessimistic). By contrast the PCM model associates the water entirely with the SIA components and scales it accordingly. 5.5 Model evaluation for PM2.5 Modelling PM2.5 and the future 40. Evaluating models that predict PM2.5 is complex due to the multiple components that make up PM2.5 mass. At one level it is possible to compare absolute mass predictions directly with PM2.5 measurements, as illustrated in Figure 5.10. The increased number of sites measuring PM2.5 in recent years will aid model evaluation in this respect. However, while useful, such a comparison is limited because it will not be known why model predictions depart from measured values, which is a critical issue for effective model evaluation. For this reason, 139
PM2.5 in the UK 140 PM2.5 concentration (µg m -3) 25 20 15 10 5 0 almost all model evaluation work that considers PM2.5 separately considers the major components that make up PM2.5 mass. Verification of source attribution as in Figure 5.10 requires corresponding measurements of chemical composition which are not available for many of the components. National network FDMS (Calibration) National network FDMS PM25 only sites Belfast Centre (6) Birmingham Tyburn (4) Bristol St Paul’s (6) Cardiff Centre (6) Chesterfield (8) Hull Freetown (6) Leamington Spa (8) Leeds Centre (4) Liverpool Speke (5) London Bloomsburry (1) Middlesbrough (6) Newcastle Centre (4) Newport (7) Oxford St Ebbes (7) Reading New Town (7) Salford Eccles (4) Sheffield Centre (4) Southampton Centre (6) Stoke-on-Trent Centre (6) Warrignton (7) York Bootham (8) National network Partisol Auchencorth Moss (10) Harwell PARTISOL (10) London N. Kengston Auchencorth Moss PM10 Black Marton (6) Conventry Memorial Park (5) Edinburgh St Leonards (6) Glasglow Centre (4) Grangrmouth (8) London Bexley (3) London Eltham (3) London Harrow London N. Kensington (2) London Teddington (3) Manchester Piccadilly (4) Nottingham Centre (6) Port Talbot Margam (8) Portsmouth (6) Preston (7) Southend-on-Sea (7) Sunderland Silksworth (5) Wigan Centre (5) Wirral Tranmere (5) Site name (DfT area type) National network Partisol PM25 only sites Bournemouth (6) Brighton Preston Park (6) London Westminster (1) Northampton (7) Port Talbot Margam Local sources Traffic (brake and tyre wear) Traffic (exhaust emissions) Urban background sources Other Shopping Aircraft Off road mobile machinery Domestic Commercial Industry Traffic (brake and tyre wear) Traffic (exhaust emissions) Urban dusts Regional background Rural dusts Secondary aerosol Long range transport primary Residual Sea Salt Measured Figure 5.10: Source apportionment for background sites in 2009 from PCM model. 41. In common with other species, the model evaluation of PM2.5 can be frustrated by a lack of information or accuracy concerning emission inventories, the chemical and physical processes involved and the availability of reliable measurements with which to compare predictions. However, in the case of PM2.5 these issues are in some situations a considerable limitation affecting the reliable evaluation of models. For example, at the local scale there is lack of knowledge concerning road vehicle tyre and brake wear, the amount of material resuspended from the ground and the contribution made by biomass. Similarly, there is also a lack of adequate information concerning NH3 emission inventories for both rural and urban sources (including the temporal variation of agricultural emissions) and the influence that they have on the assessment of model performance for particulate nitrate and ammonium and the representativeness of measurements for comparison. 42. Modelling and detailed analysis can help identify some model system deficiencies. For example, Appel et al. (2008) considered the evaluation of PM2.5 made by CMAQ version 4.5. They noted that large overprediction of particulate nitrate and ammonium in the autumn was likely the result of a large overestimation of seasonal ammonia emissions. Furthermore, the carbonaceous aerosol concentrations were substantially underpredicted during the late spring and summer months, which they considered to be due in part to the omission
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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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Page 107 and 108: PM2.5 in the UK 96 Figure 4.7: Spat
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Page 119 and 120: PM2.5 in the UK 108 4.6.1 Receptor
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Page 129 and 130: PM2.5 in the UK 118 100% 90% 80% 70
Page 131 and 132: PM2.5 in the UK 120 105. Receptor m
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Page 135 and 136: PM2.5 in the UK 124 5. At the regio
Page 137 and 138: PM2.5 in the UK 126 15. Some of the
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 (
Page 145 and 146: PM2.5 in the UK 134 with larger dev
Page 147 and 148: PM2.5 in the UK 136 Figure 5.8: UKI
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Page 153 and 154: PM2.5 in the UK 142 the North Sea (
Page 155 and 156: PM2.5 in the UK 144 53. Modelling r
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Page 159 and 160: PM2.5 in the UK 148 2. Figure A2.1.
Page 161 and 162: PM2.5 in the UK 150 6. The non-line
Page 163 and 164: PM2.5 in the UK 152 Model 50 45 40
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
Page 181 and 182: PM2.5 in the UK 170 illustrated by
Page 183 and 184: PM2.5 in the UK 172 trajectory mode
Page 187 and 188: PM2.5 in the UK 176 4. The delivery
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PM2.5 in the UK Jones A.M., Harriso
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PB13837 Nobel House 17 Smith Square
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