512 Air Pollution - WIT Press · 2014-05-12 · Air Pollution 515 4000 3500 3000 2500 2000 1500 1000 500 ppm HC A CHICAGO A-f IMP 4-PER2^ ^POLANCO UAM PER1-0,5 1 1,52,5 3 3,5 % CO

On road remote sensing of automotive CO

and HC emissions in Mexico City

J. Tejeda, V. Aquino

Institute Mexicano del Petroleo, 07730 Mexico D.F., Mexico

ABSTRACT

An analysis of the CO and hydrocarbons exhaustemissions of over 30,000 vehicles was done during tendays in February 1991, at five sites within MexicoCity using the Fuel Efficiency Automotive Test. Thistechnique, developed by the University of Denver,consists of an infrared beam that crosses a trafficroad at exhaust level and is analyzed 50 times persecond by a detector that is connected to a computerand a video camera that records the license plate ofthe vehicle being monitored. Of the 26,000 platesthat could be read, over 20,000 were from the DF and,from the Motor Vehicle Registry Data Base (Programade Placa Permanente), information about the car couldbe obtained, such as make and model year.

A global analysis of the % CO emissions vs.number of vehicles shows a broad distribution, quitedifferent from that obtained by similar studies incountries where the use of the catalytic converter iswidespread. An analysis of the distribution ofemissions vs. model year and make show how thetechnical improvements are generally reflected on adecrease of emissions on newer models. From thesemeasurements one can estimate what the result ofdifferent scraping or tune-up programs would be.

INTRODUCTION

The Mexican Petroleum Institute (IMP) and Los AlamosNational Laboratory are the coordinators of a largeproject called MARI (Mexico City Air QualityInitiative) where many institutions on both countrieshave collaborated. One part of this projectcontemplates the development of a computer model toevaluate the environmental effects of a given measureor a set of measures (strategy) to curb pollution.

Transactions on Ecology and the Environment vol 1, © 1993 WIT Press, www.witpress.com, ISSN 1743-3541

512 Air Pollution

Another part contemplates the economic and socio-political aspects.

One aspect of the problem of modeling airpollution that can always be improved is that' of theemissions inventory, and particularly that of mobilesources. The automotive fleet in Mexico is differentto that of other countries where auto emissionsmodels have been applied: for one thing, the fleet isolder and the catalytic converter is only providedfor 1991 models, as compared with the United States,where it has been the best alternative to comply withstrict emissions standards since 1974.

Fortunately, thanks to a technic developed bythe University of. Denver [1-7], it is possible tomonitor the CO and HC emissions of a large number ofvehicles in the street in normal driving conditionsusing a remote sensing device called FEAT, an acronymfor Fuel Efficiency Automotive Test. By recording thelicense plate on video, it is possible to obtain theinformation pertaining to each vehicle and thus theprofile of the actual vehicle fleet

EXPERIMENT

REMOTE SENSING INSTRUMENTATIONThe principle behind this technic is the absorptionby the exhaust gases of passing vehicles of aninfrared beam perpendicular to the flow of traffic.The University of Denver instrument consists of fourbasic units: an IR source, a detector, a computer anda video camera. The IR source is placed on one sideof a one lane traffic road and consists of a IR lampand a mirror that sends a collimated beam about 25.4cm above the roadway to a detector unit. Previousversions [1-3] of this unit split the incoming beaminto three channels having wavelength- specificdetectors for CO and C02 as well as a referencechannel. The newer version [4-6] used in thiscampaign had an added channel for HC. Data from allchannels are fed to a computer for analysis andstorage. Finally, a video camera triggered by thecomputer records a freeze-frame of the rear of thepassing vehicle as well as the date, time and themeasured emissions.

With this method, the emissions of a single carcan be measured in about a second at vehicle speedsbetween 4.0 and 240 km/h [5]. FEAT results have beencompared with those of an on-board instrumentmeasuring CO [1/6] and HC [6], giving satisfactory


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correlations.

EXPERIMENTAL SETUPFive sites where the traffic was fluid andessentially confined to one lane were selected. Thesites were chosen to represent different regions ofMexico City with correspondingly different fleetprofiles, so that the information from the licenseplate and the actual profile of the whole fleet,obtained from the Motor Vehicle Data Base (Programade Placa Permanente del Departamento del DistritoFederal), should allow one to estimate how themeasured fleet represents the whole (this work is inprogress).

RESULTS AND DISCUSSION

Table I lists the number of events, or triggers, aswell as the number of valid vehicular readings persite. The difference can be explained as pedestrians,bicycles, or noisy measurements. Of these, ValidPlates correspond to those vehicles that had alicense plate that could be read and was from theFederal District (since only this data base wasavailable). Furthermore, those corresponding toprivate cars can be distinguished from taxis ortransport vehicles.

Fig. 1 shows the averaged CO and HC emissionsmeasured at the five sites. Each mark corresponds tothe results from one day. Results are reported foronly nine days, since the first one (at IMP) was usedto check the equipment but was not calibrated. Valuesfor a similar study in the Chicago area [4] are alsoplotted. It is clear that the CO emissions in Chicagoare considerably lower than those in Mexico, whereasthe HC emissions are not that different

Emissions from PERI were expected to be lowerthan those of PER2, since the vehicles at the formerare likely to come from a higher income residentialarea than those at the latter, so that PERI carsshould be newer and better maintained. The UAM siteis in a industrial and lower income residential area,with a high number of fixed route taxis (peseros), soagain it is not surprising than the emissions arehigher than at PERI. IMP is in an industrial area,while Polanco is a high income residential area, socars here should be the newest of them all, and so tobe among the cleanest, but that was clearly not thecase. Hopefully, the license plate information wouldhelp explain this behavior.


514 Air Pollution

TABLE 1 LOCATION AND NUMBER OF VEHICLES

REGISTERED BY THE FEAT UNIT

MEXICO CITY. FEB. 1991

VALID PRIVATE

SITES TRIGGERS VEHICLES PLATES CARS

IMP

POL

UAM

PER1

PER2

5667

9935

4460

9498

5246

4822

9164

4026

8922

4904

2716

6310

2708

6350

3500

1704

5590

1815

5733

2879

TOTAL 34806 31838 21584 17721

Sites location:

IMP: North site, return lane at Eje Central Lazaro.Cardenas northbound to southbound at inter-section with Av. Montevideo north of theInstitute Mexicano del Petroleo.

POL: West site, Eastbound L.G. Urbina at A. Dumas inPolanco.

UAM: East site, lane from southbound San Rafael St.into Westbound Gavilan St., in front ofUniversidad Autonoma Metropolitana, Iztapalapa.

PERI:South site, ramp from eastbound Periferico tonorthbound Tlalpan.

PER2:South site, ramp from westbound Periferico tosouthbound Tlalpan.


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4000

3500

3000

2500

2000

1500

1000

500

ppm HC

A

CHICAGO

A

-f

IMP

4-

PER2^ ^POLANCO

UAM

PER1-

0,5 1 1,5 2,5 3 3,5

% CO

4,5 5,5

Fig. 1. Average CO vs. HC emissions for each day ofthe campaing indicating the site. Two values forChicago (reference 4) are also shown.

AGE OF FLEET (YEARS)

TOTAL

•I CHICAGO 1HZ] PER1

TAXIS

CHICAGO 2PER2

POLUAM

NON TAXIS

cm IMP

Fig. 2. Average age of all vehicles, taxis and non-taxis passing at each site. Values for Chicago fromreference 4 corresponding to the data points in Fig.1 are also shown. Taxis' age is over-estimated (seetext).


516 Air Pollution

Fig. 2 shows the average age in years for allvehicles, taxis and private cars as a function ofsite. The age for taxis should be considered an upperlimit, since it turns out that while private carlicense plates always correspond to the same vehicleuntil it is removed from circulation, taxi licenseplates can and are often sold separately from thevehicle and transfer to another car, so that in thetime that elapsed between the experiment and theprocessing of all the license plate information, someof the taxis were sold and the plates affixed tonewer models. This is particularly true in recentmonths, since there is an ongoing effort by theAuthorities to renew the taxi fleet by granting loansto buy new models.and restricting the maximum age ofa taxi.

Nevertheless, it can be seen that taxis weremuch older than private cars and that they show thesame trend among the different sites, but not assteep. As expected, the Polanco fleet is the newestand UAM the oldest. These age averages correspond toactual cars on the street, and should indicate ayounger fleet than that of all registered cars, oldercars tending to be driven less.

Before drawing any conclusion on the fleet ormaking any comparison to measurements made elsewhere,it is clear the need to understand the factors thatcaused emissions measured at Polanco to be higherthan average when they correspond to newer cars.

In order to rule out the possibility that someof the cars at Polanco were local, for example from anearby taxi stand, and that therefore cold startswere making an inordinate contribution, those carsthat had been measured more than once were checked.It turn out that very few cars were measured morethan once, and their emissions were about average.

To discard the possible effect of fleetcomposition by make, the emission values for the mostpopular make (VW) as a function of model year andsite were analyzed, and while the values for Polancowere, within the error bars, the same as those forIMP, they were statistically different from those atother sites, which very much fell together

Looking over the traffic conditions during themeasurements, it was found that at Perl, Per2 and UAMthey were very much the same, coasting at constant


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speed in front of the FEAT unit, whereas in Polancoand IMP the vehicles were, as a rule, acceleratingand even shifting gear in front of the FEAT unit. Atfirst this fact was not considered important since inthe States the average results for CO do not varymuch among different sites [1-4], but for HC [4] orwith a fleet that has no catalytic converter, siteconditions can make a big difference, as confirmedwith some cars in a dinamometer test. (For a morecomplete study of the effect of a wide range ofdriving conditions on emissions, see [6]).

It was concluded that the different trafficpatterns at the various sites could account for thedifferent emission results, and that care should betaken when drawing any conclusions: When comparing toother studies, for example in the USA, the average ofall the sites represents better the average drivingconditions encountered in the city that any one site,but if one wants to compare different parts of thefleet, one should compare each site separately orcare should be taken that these parts are equallyrepresented at all sites.

Fig. 3 show the CO and HC emissions as afunction of model year for non-taxis at Pol-IMP,UAM-Perl-Per2 and the average of all sites. There isnot as steep a dependence on model year as expectedbased on the experiences in the USA, but the effectsof the changes in technology can be seen in 1987 and1991. It is important to remember that FEAT onlygives the percentage concentrations on the exhaust,not how much exhaust is emitted. In order to be ableto compare emissions, one would need to know not onlyhow well each car burns the gasoline, but how much itburns. An ideal number would be grams of CO or HC perday for each car, and for that one would need tomultiply the number obtained by FEAT by theefficiency measured in kilometers per liter times thekilometers per day for a car. To get an idea of thefirst, one could obtain the number provided by themanufacturers for the cars when new. The second onecould be inferred from their relative frequency onour study compared to the total profile for thefleet. Were one to include only the first factor(km/It), older vehicles would indeed come out as theheaviest polluters, specially old 8 cylinders gasguzzlers. But since the price of gasoline hasincreased more than wages, these tend to be drivenless, so the two factors may cancel. We can assumethat all taxis are driven approximately the same eachday, independent of age. We intend to continue this


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I—I—I—I—I—I—I—I—I

70 72 74 76 78 80 82 84 86 88 90MODEL YEAR

% HC

01 ' 1 ' 1 ' f—' 1 ' 1 '70 72 74 76 78 80 82 84 86 88 90

MODEL YEAR

Fig. 3. Average CO and HC emissions for non-taxisversus model year for all sites and grouped by typeof site.


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work.

Fig. 4 shows normalized histograms showing assolid bars the percentage of the fleet of vehicleswith emission less than the stated percentage of COor HC category, and the contribution to the total.That is, the first two bars for CO correspond to thenumber of vehicles that emit 1% or less, and theiradded contribution; the next two bars, to thosevehicles that emit more than 1 but less than 2%, etc.

When comparing Fig. 4 for CO to those obtainedwith similar studies in Los Angeles, Denver andChicago, perhaps it is not surprising that they arequite different: In these three studies, about 70% ofall vehicles emit less than 1% CO as compared toabout 18% for this study. This is clearly an effectof the catalytic converter, where most of the carsare clean and only a small amount of cars are dirtyand contribute to most of the emissions. This doesnot seem to be the case for CO in Mexico City, wherethe distribution is wider.

What is surprising is that Fig. 4 for HC issimilar to that obtained in Chicago, at least for thelow emitters: About 82% of all vehicles emit less than0.2%, contributing about 42% to the total emissions,while for this study 77% emit less than 0.2% andcontribute to 30%. There are more vehicles at highemissions than in Chicago, but the distribution isnot as widely spread as for CO.

CONCLUSIONS

From this study of over 30,000 vehicles in five sitesin Mexico City, we conclude that FEAT is a valuabletool to estimate the CO and HC emissions of a largenumber of vehicles as they are, without any tune up,and in normal traffic conditions. From this one canestimate what the real overall vehicular emissionsinventory is, which is important to modeling efforts,and to help evaluate the effectiveness of emissionreduction measures and design new ones based on whothe heaviest polluters are.

Regarding the fleet in Mexico City, it was foundthat the vehicles emit more CO than in the USA, aclear consequence of the fact that the use ofcatalytic converters was very limited at the time ofthe study, and that if one wants to attain a certainpercent reduction of CO emissions, one would need toimprove a larger fraction of the fleet than for a


520

20-

15-

10 -

5-

o-

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34 5 6 7 8 9 10 11 12 13 14 15

PERCENT CO CATEGORY

% VEHICLES ! % CONTRIBUTION

80 if

60-

40-

20-

0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 >3.0

PERCENT HC CATEGORY

% VEHICLES % CONTRIBUTION

Fig. 4. Distribution of CO and HC concentrations forall the measured vehicles and the correspondingcontribution to the total emissions supposing all caremit the same amount of exhaust. In the CO plot,values in the 1% bar correspond to FEAT readings of0.01 to 1.0%; the 2% bar corresponds to FEAT readingsof 1.01 to 2.0%, etc.


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similar percentage in the USA. The HC emissionsdistribution resembles that of the USA (most of thecars are clean) , so that by improving or removing asmall fraction of the fleet, a noticeable effectcould be achieved. There is not such a steep effectof the age of the vehicle on the emissions asobserved in the USA.

It would be very interesting to repeat thisexperiment in the near future, since a larger numberof cars are now using the catalytic converter andtheir effect on emissions could be measured. A newversion of the FEAT apparatus that can measure NOxshould be available soon, and it could help improveour understanding of the vehicular emissionscontributions to the photochemical production ofozone, of particular importance since ozone is themain problem in Mexico City.

ACKNOWLEDGEMENTS

We would like to thank Miguel Angel Rodriguez andother personnel' at IMP, and Arturo Mercado-Huerta andthe Departamento del Distrito Federal, for theirtechnical support in the experimental gathering ofthe data, and specially Gary Bishop, Stuart Beatonand Don Stedman for the actual work in the monitoringcampaign and the preliminary processing of the dataunder contract number 9-XM1-Q063-1 with Los AlamosNational Laboratory, as well as for many fruitfuldiscussions. And to all those at the IMP that helpread all the license plates from the video tapes.

We would also like to thank the personnel atPrograma de Placa Permanente of the Departamento delDistrito Federal, and in particular to JorgeHernandez Rosas for giving us the information werequested regarding the license plates.

REFERENCES

1. Bishop, G.A.,Starkey, J.R., Ihlenfeldt, A.,Williams, W.J. and Stedman, D.H. 'IR Long PathPhotometry: A Remote Sensing Tool for AutomobileEmissions', Anal Chem 61, pp 671A - 677A, 1989

2. Stedman, D.H. and Bishop, G.A. 'An Analysis ofOn-Road Remote Sensing as a Tool for AutomobileEmissions Control', final report to the IllinoisDepartment of Energy and Natural Resources, ILENR/RE-AQ-90/05, 1990.


522 Air Pollution

3. Stedman, D.H., Bishop, G.A., Peterson, J.E. andGuenther, P.L. 'On-Road CO Remote Sensing in the LosAngeles Basin', final report to the ResearchDivision, California Air Resource Board, ContractA932-189, 1991.

4. Stedman, D.H., Bishop, G.A., Peterson, J.E. andGuenther, P.L., McVey, I.F. and Beaton, S.P. 'On-RoadCarbon Monoxide and Hydrocarbon Remote Sensing in theChicago Area', final report to the IllinoisDepartment of Energy and Natural Resources, ILENR/RE-AQ-91/14, 1991.

5. Beaton, S.P., Bishop, G.A. and Stedman, D.H.'Emission Characteristics of Mexico City Vehicles',to be published.

6. Ashbaugh, L.L., Lawson, D.R., Bishop, G.A.,Guenther, P.L., Stedman, D.H., Stephens, R.D.,Groblicki, P.J., Parikh, S.J., Johnson, B.J. andHuang, S.C. 'On-road Remote Sensing of CarbonMonoxide and Hydrocarbon Emissions During SeveralVehicle Operating Conditions' presented at AWMA/EPAConference on 'PMio Standards and NontraditionalParticulate Source Controls', Phoenix, AZ, January1992.

7. Lawson, D.R., Groblicki, P.J. Stedman, D.H.,Bishop, G.A. and Guenther, P.L. 'Emissions fromIn-use Motor Vehicles in Los Angeles: A Pilot Studyof Remote Sensing and the Inspection and MaintenanceProgram' J. Air Waste Manage. Assoc. 40,pp 1096 -1105, 1990.


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512 Air Pollution - WIT Press · 2014-05-12 · Air Pollution 515 4000 3500 3000 2500 2000 1500 1000 500 ppm HC A CHICAGO A-f IMP 4-PER2^ ^POLANCO UAM PER1-0,5 1 1,52,5 3 3,5 % CO