S.2.1.2. NO -cdn.com



Supplementary MaterialRanking current and prospective NO2 pollution mitigation strategies: an environmental and economic investigation in Oxford Street, LondonA. Jeanjeana, J. Gallagherb,c, P. S. Monksd, R. J. Leigha,?a Department of Physics and Astronomy, University of Leicester, Leicester, UK.b Department of Civil, Structural and Environmental Engineering, Trinity College Dublin, Ireland.c School of Environment, Natural Resources and Geography, Bangor University, UK.d Department of Chemistry, University of Leicester, Leicester, UK.* Corresponding author. Email address: rl40@le.ac.uk (R. J. Leigh)Figure S1: Google Earth view of the area of interest for this study, Oxford Street in the City of Westminster in London (UK). The modelled area extend on 1.2 km between the Marble Arch and Oxford Circus.S.2.1.2. NOx emission (continued)The modelling approach recommended by DEFRA for NO2 concentrations in the UK consists in two steps (i) express and simulate road emissions in terms of NOx (ii) derive street NO2 concentrations from the modelled road NOx concentrations using a NOx to NO2 calculator (DEFRA, 2016c) which takes into account average background levels of O3 and NO2. In Fig. S2, mean NO2 concentrations from a range of modelled annual mean NOx concentrations for Oxford St were calculated. The NO2 background was set to 27.7 ?g/m3 which is the estimated regional background for the City of Westminster according to the tool used (DEFRA, 2016c). The O3 background was set to 44.1 ?g/m3 (default value for the City of Westminster). The year was set to 2014, the traffic mix was set to “All London traffic” and coordinates expressed in British National Grid of 528816 m (Easting) and 181188 (Northing) corresponding to the centre of Oxford Street were added. A linear fit gives a coefficient of determination of 0.99, which shows that modelled NOx increment from road emissions have a linear relation with NO2 concentrations in Oxford St such that:[NO2] = [NOx]*0.29 + 33.8 (Eq. S1)where the first term on the right hand side corresponds to the road emission contribution and the second term to the urban background. It can be noted that the NO2 urban background has been slightly increased by the linear fit from 27.7 to 33.8 ?g/m3. It shall be noted as well that the DEFRA tool calculate mean NO2 concentrations from modelled annual mean NOx concentrations, the use of an annual average assumption therefore introduces limitations in term of temporal variation. Average daily traffic counts (counting point reference 56625 and 36435) were taken to estimate an average NOx road emissions of 280 ?g/m/s. Therefore according to Eq. S1 an average road emission of 81.2 ?g/m/s can be estimated. Figure S2: Mean NO2 concentrations were calculated from modelled annual mean NOx concentrations between 0 and 300 ?g/m3 using the DEFRA NOx to NO2 calculator. The calculations include background NO2 and O3 concentrations of 27.7 and 44.1 ?g/m3 respectively, for the reference year of 2014, the City of Westminster as the local authority and traffic mix as “All London traffic” (DEFRA, 2016c). Figure S3: Wind Rose showing the wind directions (°) and wind speeds during the year 2014 in London (data: London City Airport weather station). The wind speed and direction were recorded every 30 minutes with a resolution of 10°.Figure S4: Modelled area of Oxford Street view from inside the CFD OpenFOAM software. Coordinates are in British National Grid (UK coordinate system expressed in meter).Figure S5: Mesh used to carry out the CFD simulations which contains 3 million cells. A maximum resolution of 1.0 m was used across the X and Y axis and 0.5 m along the Z axis.Figure S6: Grid sensitivity analysis inside Oxford Street canyon, 100 points were sampled across the whole street at heights spreading between 1 to 20 m.Table S1: Installation and maintenance costs for life cycle cost analysis of different NO2 mitigation strategies (one-off installation cost; annual maintenance costs; all costs in pound sterling).ScenarioOne-off installationcostsAnnual maintenancecostsReferenceExisting trees planted in street1Narrow trees planted in street1Painted buildings2Solid barrier3Painted barrierInnovative barrier4-?120 / tree?100 / tree?3.15 / m2?125 / m?133 / m?150 / m-?10 per tree?10 per tree?3.15 / m2?2 / m?5.95 / m?2 / m1 Plant standard and narrow trees along footpath cost ?120 and ?100 per tree, respectively (cost includes trees, labour and ground excavation for planting); annual pruning of trees estimated cost of ?10 per tree.2 ?6 per litre of TiO2 paint, 1 litre of paint for 7.5 m; labour, equipment and materials estimated at ?3 per m2 for painting surfaces; re-application or cleaning of TiO2 surface annually estimated at 50 % of initial cost.3 One metre high, material and construction costs for 0.5 m deep solid wall estimated at ?100 per m length of wall; annual maintenance includes washing faces of clean wall estimated at ?2 per m length of wall.4 The wall is constructed with innovative artificial NO2 deposition material. Estimated to add an additional 20 % to the cost of constructing solid barrier wall; Same annual maintenance requirements and costs to photocatalytic wall.Table S2: Relative differences in concentrations (%) without NO2 background (traffic emissions only) on footpath and road zones for different NO2 mitigation strategies (represented as percentage reductions (-) or increases (+) to reference scenario results). Results were taken across Oxford Street on a regular 2 x 2 m grid at adult (1.5 m) height.ScenarioPedestrian zoneRoad zoneDispersionDepositionTotalDispersionDepositionTotal2. Existing tree1-0.3-0.2-0.5-0.8-0.2-1.03. Narrow tree10.5<-0.010.50.2<-0.010.24. Painted buildings2--0.8-0.8--0.4-0.45. Solid barrier-4.4--4.438.3-38.36. Painted barrier-4.4-2.1-6.538.3-2.236.17. Innovative barrier-4.4-7.3-11.738.3-7.730.61 Trees values halved to consider the yearly effects of deciduous trees (leaf free season of 6 months).2 Deposition values halved to consider half (50 %) of the building wall surface non-paintable (doors, windows, etc.).Figure S7: Influence of the wind directions on the mitigation strategies over (a,c) pedestrian zones and (c,d) road zones. ................
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