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Temporal-spatial analysis of carbon monoxide in the Mexico City Metropolitan Zone
The Science of the Total Environment, 134 (1993) 93-101 Elsevier Science Publishers B.V., Amsterdam
93
Temporal-spatial analysis of carbon monoxide in the Mexico City Metropolitan Zone Rogelio Gonzalez, Victor Paramo, Carlos Sanchez, Gabriel Perez and Ramiro Dominguez Ecology Subsecretary, Studies Direction, Rio Elba 20, Cuaunt~moc, CP. 06500, D.F., M~:~'ico
ABSTRACT This study intends to show the factors and trends of the carbon monoxide levels in the Mexico City Metropolitan Zone, applying a statistical analysis to the hourly concentration data ofearbon monoxide from 1988 to 1990. These data pertain to those of 10 monitors of the Air Quality Monitoring Network of the Metropolitan Area of Mexico City. To estimate the emission factor variations of mobile sources, as a result of some corrective measure applied by the environmental Mexican authorities, the MOBILE4 model was used.
Key words: carbon monoxide: air quality; mobile sou,'ces; Mexico City INTRODUCTION
In the Mexice City Metropolitan Zone (MCMZ), as in a]t the major metropoles of the world, urban transport joins di~,~rent economical activities, through the movement of goods and, in this case, about !5 million persons. For this reason this service is considered as one of the most important elements of the urban structure, because it gathers activities and integrates zones and functions. In 1988, the urban area was about 1292 krn2 and it is predicted that by 2000 will reach 1933 km 2. It means that the requirements of transport growing will be about 640 km 2.. Between 1982 and 1988 the number of trips/person per day (TPD) had increased by 13 035 810 (this data excludes the trips of private cars). In accordance with the figures just mentioned, an increase in transport and in the size of the fleet that will have to supply it will be inevitable. The transport network in 1988 was about 45 000 km and it is calculated that by the year 2000 about 35 000 km more will be required. *Legorreta, Jorge, 1989.Transporte y Contaminacibnen la Ciudad de M~xic¢,,Centro de E~odesarrollo. M6xico, D.F.
0048-9697/93/$06.00
@ 1993 Elsevier Science Publishers B.V. All rights re~rved
94
R. GONZALEZ ET ~...
ANTECEDENTS Different kinds of transport operate in the MCMZ and they include the following: (a) collective or public transport which includes the Ruta-100 b ~ , the Metropolitan Subway System (Metro), trolley buses, light train and, until 1991~ the Mexico State 'troncal' transport buses, (b) private transport which is composed of the various individual use vehicles such as cars, motorcycles and also vehicles used commercially, for workers and personnel transportation, ~hools and government dependencies; (c) delivering serviees, referring to vehicles devoted to grocery and merchandise transportation, and suburban and local circulating in Mexico City and; (d) suburban passenger transportation comprising private unit enterprises which serve other cities of the country. According to the 'Programs Integral de Lucha Contra ia Contaminaci6n Atmosf6rica en la Zona Metropolitans de la Ciudad de M6xico', coordinated by the lntergovernmental Technical Secretariat, the fleet of vehicles circulating in ttle Metropolitan Zone in 1990 was about 2 694 000 units (Table 1). Vehicular emissions represent 76% of total pollutants and 96% of CO released to the atmosphere, of which private cars contributed one half, taxis more than 10%, vans and minibuses 14% with the remaining emissions being emitted by delivery vehicles and gasoline buses. MEASURESAND GOALS In order to control and reduce the pollutant emissions in the MCMZ, the Secretariat of Urban Development and Ecology (SEDUE) in coordination TABLE I Main transportation indicator at the MCMZ
Private cars Taxis PermJtsionaires Rum 100 D,F, vans
Operating units
kin/day traveled (millions)
Daily trips (millions)
2 210 100 48 000 3500 2700
50.83 9.60 0.88 0.54
7.74 1.25 1.82 4.32
28 500
$,70
6.98
Mexicostate vans
9200
1.84
2.30
D.F, microbuses
5600
1,01
2.30
800
0.14
0.30
Mexocostate mierobuses
TEMPORAL-SPATIAL ANALYSIS OF CO IN MEXICO CITY
95
with the different environmental authorities, established some measures to reduce mobile sources emissions, among which the most important in relation to CO emission is the Inspection and Maintenance Program for the existing vehicular fleet (I/M Program). In this regard, the present paper will analyze the spatial-temporal variations of carbon monoxide in Mexico City and their possible relation with the measure before outlined. DATA
To carry out the spatial-temporal analysis of carbon monoxide, the air quality data generated by the RAMA (Atmospheric Monitoring Automatic Network) of the MCMZ were used. The information covers a period from 1988 to 1990 and the months of January, April, July and October were con. sideled for this analysis, assuming these months to be representative of each one of the climatic seasons of the Mexico Valley.
o A B: D F G L: N O: Q T: V; W: X; Y: Z;
CUI ]" LAHUAC TACUBA IMP TLALNEPANTLA E NEP~ACATLAN ×ALOSTOC SAN AGU$TIN NE ZAHUALCOYOTL C, DE LA ESTRELLA PEDREGAL INSUFIGEN TE8 BENITO JUAREZ MERGED HANGAFIES LAGUNtLLA
® ®
@
O AIR MONITORING STATIONS
Fig. 1. Air quality monitoring network of the Mexico City Metropolitan Zone.
96
R. GONZALEZ lET AL
Data were provided by I0 stations that were considered by the RAMA. The stations were as follows: Cuitlahuac, Merced, Pedregal, Insurgentes, Tlalnepantla, Instituto Mexicano del Petroleo (IMP), Benito Juarez, Lagunilla, San Agustin and Cerro de la Estrella [:5] (Fig. I). In relation to the met~rological parameters, the wind direction and wind speed were considered to elaborate a multidimensional analysis of the data, in order to identify the possible relations between such parameters and the CO concentrations of the study. RESULTS
Spatlal.temporalonalysis This analysis was develo~d using the hourly average of the respective month as it is shown in Fig. 2, which includes the data of' October 1989 and January 1990 at 08:00 h. In October 1989, by the m ommg, the major part '
AIR QUALITY MONITORING NETWORK OF THE MCMZ " A
C~UtTLAHUAO
=B
TAOUB~
= 0
IMP
" F
TLAI N E I ~ N T L A
O
ENEP-AOATLAN
- L
XALOSTOO
o N
,SAN AGUSTIN
- O
N~ZAHUALCOYOTL
- O
C, DE LA E S T R E L L A
-
I'
PEOREG~,L
- V
INSURG~NT(~
" W -
' 11
BENITO J U A R E Z
X
M~ROEO
- Y
HANQARES
" Z
LAGUNILLA
'l=,
C) AIR M O N I T O R I N G STATION~
UQM~
qlmQQVOl|a lUh&#~,~Qv
F~, 2, Average CO concentration October and January (08:00 h),
97
TEMFORAL-SPATIAL ANALYSIS OF CO IN MEXICO CITY
of the city was below 8 ppm in spite of this analysis being performed during a designated 'peak' period. In January the Cuitlahuac Station showed high values as a consequence of its roads with a high volume of vehicular traffic. In this figure it must be highlighted that the increase in the concentration for the same hour during January in all the City, except in the Cerro de la Estrella station, had a comparative slight increase. It is important to take into account that a correlation between this concentration (monthly average of hourly data) and the air quality standard for this pollutant (13 ppm moving average in 8 h) is not possible. For the 20:00 h sampling point in October (Fig. 3) == another period with a traffic peak -= the CO concentrations decreased slightly in relation to the rest of the day, with values of 8 ppm, excluding the Cuitlahuac and Pedregal Stations. On January 1990 a slight increase of the CO levels at Central and Northern zones during the day was observed in relation to those observed during the
AIR QUALITY MONITORING NETWORK OF T H E MCMZ - A
OUITLAHUAC
- B
TAOUBA
- D
IMP
- F
TLALNEPANTLA
- G
ENEP-AOATLAN
L
XALOgTOO
- N
8AN A G U g T I N
" 0
N E Z A H JALGOYOTL
Q
O
/
O
AIR MONITORING
STATIONS
®
C, DE LA ~ T R E L L A
- T
PEDREGAL
=V
IN~,URGI~NTE8
- W
BENITO
- X
MERCED
JUAREZ
- Y
HANGAI:I~8
- Z
LAGUNILLA
UOm/N ~oav@lo| m~p~muamv
Fig. 3. Average CO concentrationOctober and January(20:00 h).
98
R, GONZALF..ZEl" AL,
fall (October), in the same zones and also in the Southwestern sector (corresponding to the surroundings of the Pedregal station) a significant increase was reached. By night, during the month of January, CO levels were similar to those observed in October.
Factorial ana;ysis of correspondences During October 1989 (Table 2), observation was possible at night until 0600 h and wind speeds varied from 0 to 4 m/s, with wind directions coming mainly from the W (northwest and southwest) and rarely from the East (E) and North (N); the maximum average concentrations for this period, exceeded 10 ppm in the stations located at the center of the MCMZ, lnsurgentes and Merced, where the commercial and recreative activities are almost permanent all the day long. From 06:00 to 10:00 h, the wind speed did not show considerable varia. tion, the prevailing winds from the South (S) and scarcely winds from other directions. The CO concentrations vary from 5 to 10 ppm before the peak hours of vehicular activities, from 10 to 15 ppm in the peak and eventually 8~ater than 15 ppm mainly at the Cuitlahuac station, where atypical characteristics must not be forgotten. During the next daily period, which covered 10:00 to 21:00 h, the wind is higher than that of the precedent interval and it comes from the same direction ranging from 4 to 10 m/s and sometimes above these, the CO concentrations decrease from 5 to 10 ppm. Finally, during the period from 21:00 to 24:00 h, the wind speed is between
TABLE2 Summaryof results. Factorialanalysisof correspondencesOctober 1989 Hourlyclass
Monitoring station
Wind speed (mJs)
Wind direction
CO concentration (ppm)
01:00-06:00
Mercedand Insurgentes Maximum in Cuitlahuac
<4
W
>I0
None
S
4- I0
S
7- I0
N
5--10 10-15 >15 5-10 <5
06:00-10:00
10:00-21:00 21:00-24:00
All stations All stations
TEMPORAL-SPATIAL ANALYSIS OF CO IN MEXICO CITY
99
7 and 10 m/s and occasionally between 4 and 7 m/s. The predominant direction is N and the CO concentrations are below 5 ppm. In the case of January 1990 (Table 3), up to 06:00 h, the prevailing wind direction was from the SE and seldom from the NE. The wind speeds were from 0 to 4 m/s, with the exception of the ENEP-Acatlan station, where speeds above 7 m/s were recorded. The CO concentrations in all the stations reached values below 5 ppm, except at the Pedregal station, where the concentrations exceeded abnormally the 15 ppm. During the period from 06:00 to 10:00 h, the prevailing winds were from the S and exceptionally from other directions with speeds lower than 4 m/s, except for the ENEP.Acatlan station, which recorded speeds above 7 m/s. For the CO concentrations, two per!ods were distinguished, the first from 07:00 to 08:00 h and the second from 08:00 to 10:00 h, with concentrations below 5 ppm and from 5 to 10 ppm, respectively, with the exception of Cuitlahuac, IMP and Pedregal, which seldom reached values above 15 ppm. For the period comprised between 10:00 and 21:00 h, dominant winds had a southern component and speeds above 7 m/s; the CO concentrations were between 5 and 15 ppm, with the exception of Pedregal and Cuitlahuac stations which reached concentrations above 15 ppm.
TABLE 3 Summary of results. Factorial analysis of correspondences January 1990 Hourly c l a s s
Monitoring station
Wind speed (m/s)
Wind direction
CO conccntrat. (ppm)
01:00-06:00
Maximum CO in the Pedregal station
<4 > 7 in Enep Acatlan
SE
<5 >!5
06:00-10:00
All stations
<4 > 7 in Enep Acatlan
S
<5 5-10
10:00-21:00
All station CO maximum in Cuitlahuac and Pedregai
>7
S
5-15 >15
21:00-24:00
All stations Maximum CO in Pedregal station
<4
SE, NE
<5 >15
|00
R. C~NZALF2 ET AL
Finally, from 21:00 to 24:00 h, the dominant wind direction presented a southeast component, excepting some stations which recorded wind con~ponents from NE and in general, with wind sp~ds below 4 m/s, excepting ENEP-Acatlan station, where values overpassed this limit. Concentrations in general, did not exceed 5 ppm, however at the Pedregal Station, the concentrations reached values above 15 ppm. EMISSION FACTORS
The MOBILE4 model [11, allows evaluation of the emission factors of the vehicle fleet according to its technological status, driving conditions, ambient temperature, ~V~ level in gasoline, trips per day and distribution of the fleet by year-models. The original model was designed to use databases which consist of average data from the USA. such as mileage per vehicle, trips per day and basic emission rates by kind of vehicle. However, these databases are not adequate for the MCMZ fleet so then this model was modified for application in Mexico City, supposing that the vehicular fleet of the city has an operation mode similar to that existing in Denver and that the maintenance state of the fleet in Mexico was equivalent to that in Denver three years ago. This is only an approach to get a gross estimation of the impact on the emission factors in Mexico before and after the application of the I/M Program. Therefore, the current estimations to evaluate the impact of this measure on the CO emission levels must be considered with certain reservation. As is shown in Fig, 4, the impact of the I/M Program on the average emis. sion factor of the vehicles in Mexico City since its applicatien was evaluated by means of the MOBILE4 model and according with this evaluation it is possible to consider a reduction of 10%. C~)NCLUSlONS
As can b¢ observed by the analysis of the period October 1989, before the application of the I/M program to reduce and control this pollutant, the CO levels were lower by 10 ppm when the areas lnsurgcntes, Cuitlahuac and Pedr~al ~ r ¢ excluded as concentrations sometimes exceeded the threshold of 13 ppm. Therefore, considering this the comparison can only be taken as a tentative one, because it is referred to the air quality standard and our data are not compatible with it, The CO values show a very homogeneous pattern of distribution when excluding the stations mentioned previously. Based on the spatial-temporal analysi,~ for the winter time (January) a slight increase both in the diurnal and nocturnal period can be observed, probably produced by the severe
101
TEMPORAL-SPATIAL ANALYSIS OF CO IN MEXICO CITY
C.ARSON MONO,\qDE EMISIOAI FACTOR E.@I'IMATED FROM MOBIL E4 C O (or ~Kin)
7060-
!
50
i
.tO -
3 0 .... 20t0 0
WI 1t1 t/&# t"t?()(;f~Al~,'! t~EDUCtION
-
[ I
6;~ ()~i~t 6 5
[ I
6t dOf~ 6 5 t3
I I
6t ~I,# ~ 6,t8
','EAR
W I T t t O U 7 I / M DROGRANf
D
W t f H i / M PROGRAM
REDUCTION
Fig. 4. Emission factors for light duty gasoline vehicles.
meteorological conditions (stagnation), the !and use pattern, and vehicular traffic characteristics of the MCMZ. Due to the results obtained with MOBILE4 it was possible to determine minimal decrease of the emission factors. This reduction probably is not significant because of an increase in the vehicular fleet, the persistence of traffic problems and the initial condition supposed by the simulation run. REFERENCES I 2 3 4 5
Environmental Protection Agency, User's Guide to MOBILE4, North Carolina, February, 1989. World Health Organization, Criterios de Salud Ambiental No. 8, CO, Washington DC, Malzo 1980. C. Dervin. Comment Interpr6ter les r6sultats d'une analysee factorielle des correspondances, Institute Technique des C6r6ales et des Fourrages, Decembre. 1988. Secretariado T6cnico lntergubernamentai, Programa Integral Contra la Contaminaci6n Atmosf6rica en la Zona Metropolitana de la Ciudad de M6xico, M6xico, DF. 1989. SEDUE, Base de datos Meteorolbgicos y de Calidad del Aire para la gona Mctropolituna de la Ciudad de M6xico, M6xico, DF, 1991.
93
Temporal-spatial analysis of carbon monoxide in the Mexico City Metropolitan Zone Rogelio Gonzalez, Victor Paramo, Carlos Sanchez, Gabriel Perez and Ramiro Dominguez Ecology Subsecretary, Studies Direction, Rio Elba 20, Cuaunt~moc, CP. 06500, D.F., M~:~'ico
ABSTRACT This study intends to show the factors and trends of the carbon monoxide levels in the Mexico City Metropolitan Zone, applying a statistical analysis to the hourly concentration data ofearbon monoxide from 1988 to 1990. These data pertain to those of 10 monitors of the Air Quality Monitoring Network of the Metropolitan Area of Mexico City. To estimate the emission factor variations of mobile sources, as a result of some corrective measure applied by the environmental Mexican authorities, the MOBILE4 model was used.
Key words: carbon monoxide: air quality; mobile sou,'ces; Mexico City INTRODUCTION
In the Mexice City Metropolitan Zone (MCMZ), as in a]t the major metropoles of the world, urban transport joins di~,~rent economical activities, through the movement of goods and, in this case, about !5 million persons. For this reason this service is considered as one of the most important elements of the urban structure, because it gathers activities and integrates zones and functions. In 1988, the urban area was about 1292 krn2 and it is predicted that by 2000 will reach 1933 km 2. It means that the requirements of transport growing will be about 640 km 2.. Between 1982 and 1988 the number of trips/person per day (TPD) had increased by 13 035 810 (this data excludes the trips of private cars). In accordance with the figures just mentioned, an increase in transport and in the size of the fleet that will have to supply it will be inevitable. The transport network in 1988 was about 45 000 km and it is calculated that by the year 2000 about 35 000 km more will be required. *Legorreta, Jorge, 1989.Transporte y Contaminacibnen la Ciudad de M~xic¢,,Centro de E~odesarrollo. M6xico, D.F.
0048-9697/93/$06.00
@ 1993 Elsevier Science Publishers B.V. All rights re~rved
94
R. GONZALEZ ET ~...
ANTECEDENTS Different kinds of transport operate in the MCMZ and they include the following: (a) collective or public transport which includes the Ruta-100 b ~ , the Metropolitan Subway System (Metro), trolley buses, light train and, until 1991~ the Mexico State 'troncal' transport buses, (b) private transport which is composed of the various individual use vehicles such as cars, motorcycles and also vehicles used commercially, for workers and personnel transportation, ~hools and government dependencies; (c) delivering serviees, referring to vehicles devoted to grocery and merchandise transportation, and suburban and local circulating in Mexico City and; (d) suburban passenger transportation comprising private unit enterprises which serve other cities of the country. According to the 'Programs Integral de Lucha Contra ia Contaminaci6n Atmosf6rica en la Zona Metropolitans de la Ciudad de M6xico', coordinated by the lntergovernmental Technical Secretariat, the fleet of vehicles circulating in ttle Metropolitan Zone in 1990 was about 2 694 000 units (Table 1). Vehicular emissions represent 76% of total pollutants and 96% of CO released to the atmosphere, of which private cars contributed one half, taxis more than 10%, vans and minibuses 14% with the remaining emissions being emitted by delivery vehicles and gasoline buses. MEASURESAND GOALS In order to control and reduce the pollutant emissions in the MCMZ, the Secretariat of Urban Development and Ecology (SEDUE) in coordination TABLE I Main transportation indicator at the MCMZ
Private cars Taxis PermJtsionaires Rum 100 D,F, vans
Operating units
kin/day traveled (millions)
Daily trips (millions)
2 210 100 48 000 3500 2700
50.83 9.60 0.88 0.54
7.74 1.25 1.82 4.32
28 500
$,70
6.98
Mexicostate vans
9200
1.84
2.30
D.F, microbuses
5600
1,01
2.30
800
0.14
0.30
Mexocostate mierobuses
TEMPORAL-SPATIAL ANALYSIS OF CO IN MEXICO CITY
95
with the different environmental authorities, established some measures to reduce mobile sources emissions, among which the most important in relation to CO emission is the Inspection and Maintenance Program for the existing vehicular fleet (I/M Program). In this regard, the present paper will analyze the spatial-temporal variations of carbon monoxide in Mexico City and their possible relation with the measure before outlined. DATA
To carry out the spatial-temporal analysis of carbon monoxide, the air quality data generated by the RAMA (Atmospheric Monitoring Automatic Network) of the MCMZ were used. The information covers a period from 1988 to 1990 and the months of January, April, July and October were con. sideled for this analysis, assuming these months to be representative of each one of the climatic seasons of the Mexico Valley.
o A B: D F G L: N O: Q T: V; W: X; Y: Z;
CUI ]" LAHUAC TACUBA IMP TLALNEPANTLA E NEP~ACATLAN ×ALOSTOC SAN AGU$TIN NE ZAHUALCOYOTL C, DE LA ESTRELLA PEDREGAL INSUFIGEN TE8 BENITO JUAREZ MERGED HANGAFIES LAGUNtLLA
® ®
@
O AIR MONITORING STATIONS
Fig. 1. Air quality monitoring network of the Mexico City Metropolitan Zone.
96
R. GONZALEZ lET AL
Data were provided by I0 stations that were considered by the RAMA. The stations were as follows: Cuitlahuac, Merced, Pedregal, Insurgentes, Tlalnepantla, Instituto Mexicano del Petroleo (IMP), Benito Juarez, Lagunilla, San Agustin and Cerro de la Estrella [:5] (Fig. I). In relation to the met~rological parameters, the wind direction and wind speed were considered to elaborate a multidimensional analysis of the data, in order to identify the possible relations between such parameters and the CO concentrations of the study. RESULTS
Spatlal.temporalonalysis This analysis was develo~d using the hourly average of the respective month as it is shown in Fig. 2, which includes the data of' October 1989 and January 1990 at 08:00 h. In October 1989, by the m ommg, the major part '
AIR QUALITY MONITORING NETWORK OF THE MCMZ " A
C~UtTLAHUAO
=B
TAOUB~
= 0
IMP
" F
TLAI N E I ~ N T L A
O
ENEP-AOATLAN
- L
XALOSTOO
o N
,SAN AGUSTIN
- O
N~ZAHUALCOYOTL
- O
C, DE LA E S T R E L L A
-
I'
PEOREG~,L
- V
INSURG~NT(~
" W -
' 11
BENITO J U A R E Z
X
M~ROEO
- Y
HANQARES
" Z
LAGUNILLA
'l=,
C) AIR M O N I T O R I N G STATION~
UQM~
qlmQQVOl|a lUh&#~,~Qv
F~, 2, Average CO concentration October and January (08:00 h),
97
TEMFORAL-SPATIAL ANALYSIS OF CO IN MEXICO CITY
of the city was below 8 ppm in spite of this analysis being performed during a designated 'peak' period. In January the Cuitlahuac Station showed high values as a consequence of its roads with a high volume of vehicular traffic. In this figure it must be highlighted that the increase in the concentration for the same hour during January in all the City, except in the Cerro de la Estrella station, had a comparative slight increase. It is important to take into account that a correlation between this concentration (monthly average of hourly data) and the air quality standard for this pollutant (13 ppm moving average in 8 h) is not possible. For the 20:00 h sampling point in October (Fig. 3) == another period with a traffic peak -= the CO concentrations decreased slightly in relation to the rest of the day, with values of 8 ppm, excluding the Cuitlahuac and Pedregal Stations. On January 1990 a slight increase of the CO levels at Central and Northern zones during the day was observed in relation to those observed during the
AIR QUALITY MONITORING NETWORK OF T H E MCMZ - A
OUITLAHUAC
- B
TAOUBA
- D
IMP
- F
TLALNEPANTLA
- G
ENEP-AOATLAN
L
XALOgTOO
- N
8AN A G U g T I N
" 0
N E Z A H JALGOYOTL
Q
O
/
O
AIR MONITORING
STATIONS
®
C, DE LA ~ T R E L L A
- T
PEDREGAL
=V
IN~,URGI~NTE8
- W
BENITO
- X
MERCED
JUAREZ
- Y
HANGAI:I~8
- Z
LAGUNILLA
UOm/N ~oav@lo| m~p~muamv
Fig. 3. Average CO concentrationOctober and January(20:00 h).
98
R, GONZALF..ZEl" AL,
fall (October), in the same zones and also in the Southwestern sector (corresponding to the surroundings of the Pedregal station) a significant increase was reached. By night, during the month of January, CO levels were similar to those observed in October.
Factorial ana;ysis of correspondences During October 1989 (Table 2), observation was possible at night until 0600 h and wind speeds varied from 0 to 4 m/s, with wind directions coming mainly from the W (northwest and southwest) and rarely from the East (E) and North (N); the maximum average concentrations for this period, exceeded 10 ppm in the stations located at the center of the MCMZ, lnsurgentes and Merced, where the commercial and recreative activities are almost permanent all the day long. From 06:00 to 10:00 h, the wind speed did not show considerable varia. tion, the prevailing winds from the South (S) and scarcely winds from other directions. The CO concentrations vary from 5 to 10 ppm before the peak hours of vehicular activities, from 10 to 15 ppm in the peak and eventually 8~ater than 15 ppm mainly at the Cuitlahuac station, where atypical characteristics must not be forgotten. During the next daily period, which covered 10:00 to 21:00 h, the wind is higher than that of the precedent interval and it comes from the same direction ranging from 4 to 10 m/s and sometimes above these, the CO concentrations decrease from 5 to 10 ppm. Finally, during the period from 21:00 to 24:00 h, the wind speed is between
TABLE2 Summaryof results. Factorialanalysisof correspondencesOctober 1989 Hourlyclass
Monitoring station
Wind speed (mJs)
Wind direction
CO concentration (ppm)
01:00-06:00
Mercedand Insurgentes Maximum in Cuitlahuac
<4
W
>I0
None
S
4- I0
S
7- I0
N
5--10 10-15 >15 5-10 <5
06:00-10:00
10:00-21:00 21:00-24:00
All stations All stations
TEMPORAL-SPATIAL ANALYSIS OF CO IN MEXICO CITY
99
7 and 10 m/s and occasionally between 4 and 7 m/s. The predominant direction is N and the CO concentrations are below 5 ppm. In the case of January 1990 (Table 3), up to 06:00 h, the prevailing wind direction was from the SE and seldom from the NE. The wind speeds were from 0 to 4 m/s, with the exception of the ENEP-Acatlan station, where speeds above 7 m/s were recorded. The CO concentrations in all the stations reached values below 5 ppm, except at the Pedregal station, where the concentrations exceeded abnormally the 15 ppm. During the period from 06:00 to 10:00 h, the prevailing winds were from the S and exceptionally from other directions with speeds lower than 4 m/s, except for the ENEP.Acatlan station, which recorded speeds above 7 m/s. For the CO concentrations, two per!ods were distinguished, the first from 07:00 to 08:00 h and the second from 08:00 to 10:00 h, with concentrations below 5 ppm and from 5 to 10 ppm, respectively, with the exception of Cuitlahuac, IMP and Pedregal, which seldom reached values above 15 ppm. For the period comprised between 10:00 and 21:00 h, dominant winds had a southern component and speeds above 7 m/s; the CO concentrations were between 5 and 15 ppm, with the exception of Pedregal and Cuitlahuac stations which reached concentrations above 15 ppm.
TABLE 3 Summary of results. Factorial analysis of correspondences January 1990 Hourly c l a s s
Monitoring station
Wind speed (m/s)
Wind direction
CO conccntrat. (ppm)
01:00-06:00
Maximum CO in the Pedregal station
<4 > 7 in Enep Acatlan
SE
<5 >!5
06:00-10:00
All stations
<4 > 7 in Enep Acatlan
S
<5 5-10
10:00-21:00
All station CO maximum in Cuitlahuac and Pedregai
>7
S
5-15 >15
21:00-24:00
All stations Maximum CO in Pedregal station
<4
SE, NE
<5 >15
|00
R. C~NZALF2 ET AL
Finally, from 21:00 to 24:00 h, the dominant wind direction presented a southeast component, excepting some stations which recorded wind con~ponents from NE and in general, with wind sp~ds below 4 m/s, excepting ENEP-Acatlan station, where values overpassed this limit. Concentrations in general, did not exceed 5 ppm, however at the Pedregal Station, the concentrations reached values above 15 ppm. EMISSION FACTORS
The MOBILE4 model [11, allows evaluation of the emission factors of the vehicle fleet according to its technological status, driving conditions, ambient temperature, ~V~ level in gasoline, trips per day and distribution of the fleet by year-models. The original model was designed to use databases which consist of average data from the USA. such as mileage per vehicle, trips per day and basic emission rates by kind of vehicle. However, these databases are not adequate for the MCMZ fleet so then this model was modified for application in Mexico City, supposing that the vehicular fleet of the city has an operation mode similar to that existing in Denver and that the maintenance state of the fleet in Mexico was equivalent to that in Denver three years ago. This is only an approach to get a gross estimation of the impact on the emission factors in Mexico before and after the application of the I/M Program. Therefore, the current estimations to evaluate the impact of this measure on the CO emission levels must be considered with certain reservation. As is shown in Fig, 4, the impact of the I/M Program on the average emis. sion factor of the vehicles in Mexico City since its applicatien was evaluated by means of the MOBILE4 model and according with this evaluation it is possible to consider a reduction of 10%. C~)NCLUSlONS
As can b¢ observed by the analysis of the period October 1989, before the application of the I/M program to reduce and control this pollutant, the CO levels were lower by 10 ppm when the areas lnsurgcntes, Cuitlahuac and Pedr~al ~ r ¢ excluded as concentrations sometimes exceeded the threshold of 13 ppm. Therefore, considering this the comparison can only be taken as a tentative one, because it is referred to the air quality standard and our data are not compatible with it, The CO values show a very homogeneous pattern of distribution when excluding the stations mentioned previously. Based on the spatial-temporal analysi,~ for the winter time (January) a slight increase both in the diurnal and nocturnal period can be observed, probably produced by the severe
101
TEMPORAL-SPATIAL ANALYSIS OF CO IN MEXICO CITY
C.ARSON MONO,\qDE EMISIOAI FACTOR E.@I'IMATED FROM MOBIL E4 C O (or ~Kin)
7060-
!
50
i
.tO -
3 0 .... 20t0 0
WI 1t1 t/&# t"t?()(;f~Al~,'! t~EDUCtION
-
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6t dOf~ 6 5 t3
I I
6t ~I,# ~ 6,t8
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W I T t t O U 7 I / M DROGRANf
D
W t f H i / M PROGRAM
REDUCTION
Fig. 4. Emission factors for light duty gasoline vehicles.
meteorological conditions (stagnation), the !and use pattern, and vehicular traffic characteristics of the MCMZ. Due to the results obtained with MOBILE4 it was possible to determine minimal decrease of the emission factors. This reduction probably is not significant because of an increase in the vehicular fleet, the persistence of traffic problems and the initial condition supposed by the simulation run. REFERENCES I 2 3 4 5
Environmental Protection Agency, User's Guide to MOBILE4, North Carolina, February, 1989. World Health Organization, Criterios de Salud Ambiental No. 8, CO, Washington DC, Malzo 1980. C. Dervin. Comment Interpr6ter les r6sultats d'une analysee factorielle des correspondances, Institute Technique des C6r6ales et des Fourrages, Decembre. 1988. Secretariado T6cnico lntergubernamentai, Programa Integral Contra la Contaminaci6n Atmosf6rica en la Zona Metropolitana de la Ciudad de M6xico, M6xico, DF. 1989. SEDUE, Base de datos Meteorolbgicos y de Calidad del Aire para la gona Mctropolituna de la Ciudad de M6xico, M6xico, DF, 1991.