车辆排放扩散模型.pdf

ELSEVIEI The Science of the Total Environment 189 190 1996 321 326 CAR International a simple model to determine city street air quality J den Boeft H C Eerensb W A M den Tonkelaar P Y J Zandveld Department of Environmental Chemistry TN0 Institute of Enivronmental Sciences Schoemakerstraat 97 P O Box 601 I 2600 JA De Motor vehicles Dispersion model 1 Introduction Traffic is the predominant source of pollution in cities In busy streets in most countries it is to be expected that the Air Quality Guidelines e g for NO CO benzene suspended particulates and lead will be exceeded l Continuous monitoring of the air quality in such streets however will be very costly and impracticable Model calculations Corresponding author Tel 31 15 696016 fax 31 15 617217 e mail denboeft mw tno nl are a useful alternative to measuring However the existing line source models assume either ho mogeneous terrain around the source or a street canyon configuration 2 It is well known that buildings have a very strong and complicated influence on the flow of air in the direct vicinity 2 The long term yearly average concentration however is much less sen sitive to building structure than is often assumed In most countries a part of the Air Quality Stan dards is based on 98 percentiles of the frequency distribution of concentrations By analyzing mea surements near traffic it was found that the ratio 0048 9697 96 15 00 0 1996 Elsevier Science B V All rights reserved PII SOO48 9697 96 05226 6 322 J den Boeft et al 1 The Science of the Total Environment i89 190 1996 321 326 between annual averages and the high percentile NO concentrations from the calculated local values did not vary very much from street to traffic contribution of NO and the estimated street background ozone concentrations To find a relation between emissions and con centrations for various road types an extensive programme of wind tunnel experiments was car ried out for 49 confi rations which differed with respect to dimensions distances and shapes of streets their buildings and trees 2 Each configu ration contained l 5 receptor points at a full scale height of 1 5 m Since the variation of pollutant con ntration with wind speed and sta bility is relatively well known for most conditions the experiments focused on the effects of wind direction on the concentrations In the analysis of the results two contributions were distinguished The so called direct contribution arises from pol lution that reaches the receptor without first being brought upward in the wake of the building The other contribution called recirculation is caused by pollution that has first been transported in the wake behind the building or between buildings before reaching the receptor The most prominent findings are The contribution of recirculation is much smaller than the direct contribution blown di rectly to the receptor and does not exhibit strong gradients near the source The shape of the concentration wind rose near corners of buildings e g at street intersections proved to be difficult to explain in detail Aver aged over all wind directions the concentra tions could be described reasonably well with the above mentioned concepts 2 CAR International 2 1 Basic principies A simpler version of the model described above was derived to calculate air quality in city streets This version called CAR calculation of air pollu tion near roads consists of the elements emission dilution and background concentrations 4 The emission is calculated from data on annually aver aged traffic density vehicle distribution and speed To characterize the driving pattern and emission strength of the traffic four classes of average speed situations were defined moto ays other roads around cities normal city traffic and stagnating city traffic In combination with the corresponding emission factors the user can define his own speed classification In CAR International the kerbside is defined as the receptor being the closest place to traffic normally occupied by pedestrians according to the definitions for the Dutch air quality limits 4 Pollutant concentrations are calculated at a height of 1 5 m above the pavement for distances from the receptor point to the road axis of between 5 and 30 m Rows of trees in a street have a variable effect on the concentration pattern varying from slightly lowering to strongly increasing the con centration The results were incorporated into a previous Gaussian plume type model for the dispersion of traffic exhausts called TN0 traffic model 131 In this model the traffic is represented by line sources divided into series of small point sources The model calculates the wind direction at receptors near roads Further the model uses the depen dence of the con ntration on wind direction to estimate the shape of the frequency distribution A semi empirical relation is used to determine It is well known that buildings have a very strong and complicated influence on the flow of air in the immediate vicinity To characterize the dilution of the exhaust a set of street types was defined based on the most important building characteristics see Fig 1 2 2 Model design In CAR International the calculations are per formed in Iive steps 1 City background level C The value of the city background has to be derived from mea surements or has to be estimated Otherwise the background level is calculated as the sum of regional background and a city specific contribution proportional to the city surface area default values J den Boefi et al The Science of the Total Environment i89 190 1996 321 326 323 Fig 1 Street types as defined in CAR International Type 1 Road in open terrain No buildings or trees in the near vicinity Type 2 Basic street type all roads not defined by 1 3A 3B or 4 Type 3A Broad road with buildings on both sides Type 3B Street canyon buildings on both sides Type 4 Street with buildings at least 3 m high on one side 2 3 4 C C aF 1 where C is regional background concentra tion in g m3 annual average CI is city back ground increment per km in pgg m3 F is diameter of built up city area in km Local street emission I Et 1 FJNE FJVEJ 24 x 3600 2 F is fraction of heavy duty traffic and buses N is the number of vehicles per day E is emission factor for passenger cars in ug m per vehicle depends on speed E is emission factor for heavy duty traffic and buses in g m per vehicle depends on speed Street specific contribution to average concen trations C G q is street type dilution function s m ex plained in Fig 2 Ft accounts for the effects of trees on wind velocity 1 00 1 25 or 1 50 W is a standard wind speed in The Netherlands m s W is the regional user wind speed at 10 m height m s Annual average concentration Ca and per centiles C ca c c 4 q P Ct CL4 5 5 P is the ratio between percentile and annual average concentration P depends on street type and component and is determined exper imentally by data analysis Traffic contribution to the NO concentration C oJ The module for the calculation of the NO concentration was derived from the more elaborate TN0 traffic model 3 see Section 1 Y NOZ FNO NO ct No t NO F is the fraction of NO directly NNGi empirically derived Ct NO is 6 emitted as the traffic O 0 5 10 15 20 25 30 35 m Fig 2 The ratio of the 9 percentile of 8 h averaged concen trations of CO and the average emission as a function of the distance to the road axis x 324 I den Boeft et al The Science of the Total Environment 189 190 1996 321 326 Table 1 Comparison of meaanred and calculated concentrations at eleven measuring stations in the Netherlands for 1990 in pg m 3 4 Station street type CO 98 p NO average as pg m3 NO NO2 98 p CAR Meas CAR Meas CAR Meas Utrecht 1 2 2550 2800 179 163 123 110 Utrecht 2 3B 5250 6400 332 401 143 151 Utrecht 3 3A 3350 3200 184 184 124 134 Utrecht 4 3A 2850 3100 157 207 120 121 Apeldoom 1 2 2950 2700 144 120 108 97 Apeldoom 2 3A 2800 3000 153 148 109 108 Apeldoom 3 2 2900 2800 135 122 106 91 Eindhoven 1 4 3250 3700 178 165 118 105 Eindhoven 2 4 3050 3400 248 190 127 109 Eindhoven 3 4 3650 3400 328 226 134 118 Haarlem 2 4400 4300 199 182 131 132 Difference 3 C is the regional background concentration of ozone 3 is the fraction of O3 available for reaction with NO depending on street type K is an empirical parameter The dilution function 4 s m is an empirical polynomial using the distances of the receptor point to the road axis as a variable The form of the polynomial was for the various street types calculated by the TN0 traffic model 3 As an example CO is shown in Fig 2 2 3 Input data CAR International distinguishes general input parameters from inputs specific to traffic and geometry data of each road The following input parameters have to be defined by the user otherwise the model uses default values Emission factors of CO g km per vehicle Parameter Unit Emission factors of CO NO benzene lead g km per vehicle black smoke and a user defined compo nent o es nding to the chosen speed classification Percentage directly emitted NOz City background con uglm3 centrations Regional background a m3 co ntrations Yearly average wind m s speed at 10 m height The necessary traffic and geometry input data one set for each road are number of vehicles per day percentage heavy duty traffic and buses dis tance road axis to exposure area speed type road type tree factor E 3 Accuracy of CAR International The CAR model was applied to the streets stations of the Dutch National Air Monitoring Network 4 For the various street types the results are given in Table 1 for CO annual 98 percentile of 8 h averages NO annual average and NO annual 9X percentile of 1 h averages The calculations are corrected for differences in height CAR 1 5 m street stations 2 5 m by multiplying the calculated street cont butions for CO and NO by 0 91 4 Table 2 J den Boeft et al The Science of the Total Environment 189 190 1996 321 326 325 Comparison of measured and calculated concentrations at measuring stations in Lancaster UK and Guanzhou China in pg rn Country street CO 98 p CAR Meas NO average as pg m3 NO NO mean CAR Meas CAR Meas Lancaster UK Boweham Road King Street Meeting House Lane 37 38 64 63 42 51 Guanzhou China East Huanshi Road Fifth Zhongshan Road Renmin Road 4000 3200 180 190 3000 5500 160 150 9000 11000 300 330 Another comparison was made by Heida S with measurements in ten streets in Amsterdam Averaged over ten streets the differences be tween calculations and measurements were 10 f 12 for the 98 percentile of CO and 6 f 10 for the 98 percentile of NO It can be concluded that the CAR model is a sufficiently reliable and feasible method for calculation of traffic related air pollutants in urban streets and that the accuracy is well within the limits as set by the Dutch Air Quality decrees 30 at 70 confidence level a7 aa a9 90 91 92 93 94 Year Fig 3 Total number of Dutch houses where air quality limits were exceeded during the period 1987 1994 NO P98 value of 135 pg m average B a P 0 001 pg m3 and average benzene 10 dm3 A preliminary version of the CAR Interna tional model was sent to some other countries to evaluate the usefulness and accuracy for other users The results obtained for Lancaster UK and Guanzhou Canton in China are given in Table 2 As a first comparison the results are rather good The agreement between the calculated and measured concentrations of CO should perhaps be improved Problems for the calculation arose in the definition of correct emission factors and city background concentrations 4 Technical specifications and applications of CAR International CAR International has been developed for local applications in cities 5 30 m from road axes The model is suitable for a variety of street types and can perform calculations for a maximum of 100 streets The concentrations calculated relate to both non reactive CO benzene soot lead and a user defined substance and reactive NO pol lutants CAR International calculates annual av erage concentrations and 98 percentiles of 1 8 and 24 h average concentrations The model is equipped with two output options the results can be shown on the PC monitor or printed in tabular form CAR International runs on any IBM compat ible personal computer under Windows version 326 I den Boefi et al The Science of the Total Environment 189 190 1996 321 326 3 0 or later including Windows 95 Depending on the PC processor and the number of streets the central processing unit CPU time is several minutes or less CAR International is available as a Windows version supplied on a 3 5 inch floppy disk together with an extensive manual A demo version of the model can be obtained on request In the Netherlands CAR has been used for a yearly survey of air quality in Dutch cities 6 It is also used as a judgment tool to assess Traffic Management Plans 4 and for scenario studies As an example of the last application the total number of Dutch houses where air quality limits were exceeded for the period 1987 1994 is shown in Fig 3 The results indicate that the air quality in city streets is improving 5 Conclusions CAR International is a model to determine city street air quality yearly averages and percen tiles The model is based on wind tunnel experi ments theoretical considerations and measure ments It is a validated and feasible method for which the input data are readily available T