Journal of Environmental Protection, 2013, 4, 40-49
http://dx.doi.org/10.4236/jep.2013.48A1006 Published Online August 2013 (http://www.scirp.org/journal/jep)
Diurnal and Seasonal Variation of BTX in Ambient air of
One Urban Site in Carmen City, Campeche, Mexico
J. G. Cerón1*, E. Ramírez2, R. M. Cerón1, C. Carballo1, C. Aguilar1, U. López2, A. Ramírez2,
Y. Gracia2, D. Naal1, A. Campero1, J. Guerra1, E. Guevara1
1Universidad Autónoma del Carmen, Ciudad del Carmen, Mexico; 2Facultad de Ciencias Químicas, Universidad Autónoma de
Nuevo León (UANL), San Nicolás de los Garza, Mexico.
Received June 11th, 2013; revised July 12th, 2013; accepted August 3rd, 2013
Copyright © 2013 J. G. Cerón et al. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
ABSTRACT
BTX (benzene, ethylbenzene, toluene and p-xylene) and meteorological parameters were measured in ambient air of an
urban site located in Carmen City, Campeche, Mexico. A total of 412 samples were collected for BTX and analyzed by
Gas Chromatography with Flame Ionization Detection (GC-FID). Meteorological parameters were measured by a port-
able station. A marked diurnal variation was found for all measured BTX. The highest concentrations occurred during
midday (13:00-14:30 h). A clear seasonal pattern was observed too for all compounds registering their highest levels
during summer sampling period. Mean concentrations for benzene, ethylbenzene, toluene and p-xylene were: 5.42, 3.97,
11.24 and 8.32 ppbv, respectively. BTX abundance showed the following order: toluene > p-xylene > benzene > ethyl-
benzene. BTX maximum concentrations were found when winds blowed from E and NE. Important oil industry sources
and avenues are located at these directions. These sources could contribute to the levels of BTX in this site.
Keywords: BTX; Carbonyls; Volatile Organic Compounds; Air Pollution; Carmen City; Mexico
1. Introduction
Reductions in air pollutants emissions have been made
from many sources over the world. In spite of volatile
organic compounds (VOCs) and their effects on public,
health is still a concern and an unsolved problem in many
urban cities. Spatial and temporal concentrations patterns
outdoors of VOCs are complex; they are originated from
different sources, and they are reactive compounds. All
of these characteristics make them a difficult challenge
for environmental policy makers [1]. In urban areas,
these compounds are important atmospheric pollutants
because of such detrimental effects as their contribution
to stratospheric ozone depletion, tropospheric photo-
chemical ozone formation, toxic and carcinogenic human
health effects, and enhancement of the global greenhouse
effect [2,3].
Benzene and its alkyl derivatives belong to the VOCs
group commonly named as BTX and they are especially
harmful for human health, because of their toxic,
mutagenic carcinogenic properties [4].
In order to develop efficient air pollution abatement
strategies for BTX, it is important to determine their
concentrations and to identify their sources and behaviors
in ambient air of urban areas [5-7].
Measurements of BTX in some urban areas of Mexico
have been carried out, but most of them have been fo-
cused to big cities like the Metropolitan Areas of Mexico
City and Monterrey [8-11].
At the southeast of the country is located Carmen City,
which has experimented an accelerated development
since 1996 due to it is an urban area located near from
the most important oil offshore platforms in Mexico. In
addition, the most important source gas recompression
station is located at 25 km from this city. Demographic
growth and floating population working for oil industry
have been increased in this island last 15 years. For all
these reasons its inhabitants are starting to face problems
of air quality every day. The objective of this research
was to determine the atmospheric concentrations of some
BTX (benzene, toluene, ethylbenzene and p-xylene) at
one site located in Carmen City, Campeche, Mexico
during three seasons of 2012 (spring, summer and au-
tumn) and to try to infer their probable sources from a
*Corresponding author.

Diurnal and Seasonal Variation of BTX in Ambient air of One Urban Site in Carmen City, Campeche, Mexico 41
meteorological analysis.
2. Methodology
2.1. Site Description
The study was conducted in a site located within the Bo-
tanical Garden of the Autonomous University of Carmen
(Lat. 18˚38'36''N, Long. 91˚49'51''W, elev. 2 masl) on the
southeast edge of Carmen Island in Campeche, Mexico
(Figure 1). According to the Köeppen classification
modified by Garcia [12], the climate is sub-humid warm
with summer rains. The average annual rainfall is 1393.1
mm and the average annual temperature is 27.2˚C. Winds
prevail from NE and SE all year around and blow at an
average speed of 1.4 ms−1 [12]. This site is within the
Natural Protected Area named “Términos Lagoon”.
2.2. Sampling Method
412 samples were collected from June 1 to December 21,
2012, considering three climatic seasons: spring, summer
and autumn 2012. Benzene, ethyl benzene, toluene and
p-xylene were measured in ambient air.
Samples of air were collected within glass tubes con-
taining 226-01 Anasorb CSC (SKC): length 70 mm; in-
ner diameter 4.0 mm; outer diameter 6 mm packed in the
first section with 100 mg of actived carbon and 500 mg
in the second one, separated by a glass wool section
(Method INSHT MTA/MA-030/A92) [13,24]. The down-
stream end of the glass tube was connected to a cali-
brated flow meter. Ambient air was passed through the
glass tubes at a flow rate of 200 ml·min−1 at 1.5-hour
intervals (day, midday and afternoon). Sampling was
carried out using a Universal XR pump model PCXR4
(SKC), at three sampling periods: B1 (from 08:00 to
09:30 h), B2 (from 13:00 to 14:30 h) and B3 (from 16:00
Sampling site
18°38’36”Ny91°49’51”W
Sampling site
Figure 1. Location of the sampling site.
to 17:30 h). During sampling, the Swagelok® fitting was
removed from the marked end, and a diffusion cap was
fitted to the end of the sampling tube. Prior to the main
study, several pilot experiments were conducted to evalu-
ate the suitability of the sampling procedure intended for
use in the main study. This procedure included deter-
mining appropriate sampling times. Samplers tubes were
protected from bad weather conditions by aluminum
shelters. After the exposure time, the adsorption tubes
were labeled and capped tightly with PTFE caps and
transferred to the laboratory in cold boxes. This proce-
dure was applied to both clean and sample tubes for
storage prior to use or analysis. Field blanks were trans-
ported along with samplers to the field and stored in the
laboratory during the sampling period. Samples were
analyzed within three weeks after sample collection at
the Environmental Sciences Laboratory in the Autono-
mous University of Carmen City (UNACAR).
2.3. Analytical Method
Samples were extracted with 1 ml of CS2 for each sec-
tion of the samplers tubes, shaking during 30 s to assure
a maximum desorption. Extracted samples were analyzed
using a TRACE GC Ultra gas chromatograph (Thermo-
scientific) and one flame ionization detector (FID;
Thermoscientific Technologies, Inc) (Method INSHT
MTA/MA-030/A92) [13,24]. The analytical column used
was a capillary column (57 m, 0.32 mm i.d., 0.25 μm
film thickness). Operation of the instrument was con-
trolled using a Trace Chemstation data system. The oven
temperature program was initially set to 40˚C for 4 min,
which was then increased at a rate of 5˚C/min up to
100˚C, and was finally maintained for 10 min at 100˚C.
The FID temperature was set to 250˚C using a hydro-
gen/air flame with constant flows of 35 ml·min−1 and 350
ml·min−1 for ultra-pure hydrogen and extra-dried air,
respectively. The ultra-pure nitrogen carrier
(99.999%) gas flow rate was 1 ml·min−1 [14]. Four
BTX that included benzene, p-xylene, ethyl benzene, and
toluene, were investigated. Five-point calibration was
performed using 99.98% Sigma-Aldrich anaytical re-
agents at a concentration of 2 ppm for each BTX.
The established calibration curves for the four investi-
gated BTX were found to have R-squarevalues of 0.999.
Method detection limit (MDL) for each compound was
calculated by multiplying the standard deviation obtained
from seven replicate measurements of the first level of
calibration by 3.14 (Student’s t-value). The analytical
results showed that the MDLs for the four VOC com-
pounds of benzene, ethyl benzene, p-xylene, and toluene,
were 0.0517; 0.0566; 0.0600; 0.025; μg·m−3, respectively.
The amount of BTX in blank samples was below the
limit of detection (LOD) for all studied compounds.

Diurnal and Seasonal Variation of BTX in Ambient air of One Urban Site in Carmen City, Campeche, Mexico
42
2.4. Monitoring of Meteorological Parameters
Wind conditions (direction and speed), relative humidity,
temperature, and barometric pressure were monitored
from June 1 to December 21, 2012 (spring, summer and
autumn). A portable meteorological station Davis Van-
tage Pro II model was used in order to measure the me-
teorological parameters. Wind roses were constructed for
each day using the software WRPLOT (from Lakes En-
vironmental) [15]. 24 hr back air masses trajectories were
calculated for the studied period using HYSPLIT model
from the NOAA (National Oceanic Administration
Agency, USA) in order to identify the probable origin of
the air masses.
3. Results
3.1. Diurnal and Seasonal Variation of BTX
Benzene (Bz) and Toluene (T) showed the same diurnal
pattern registering the highest concentrations during the
midday (B2) decreasing during the afternoon (B3) and
showing the lowest values during the mornings (B1).
Ethylbenzene (EBz) and p-Xylene (p-X) had the same
behavior along the day with the highest levels during the
midday (B2) decreasing during the mornings (B1) and
registering their lowest concentrations during the after-
noons (B3) as it can be observed in Figure 2.
In Table 1 is shown the comparison of the results of
this study with ambient air concentrations found in other
sites around the world. It can be observed that BTX lev-
els found in this study are comparable to those reported
for cities like Mexico [8,22] and Hong Kong [18] and
lower than those measured in Rome [16].
All measured BTX showed the same seasonal varia-
tion, registering the highest concentrations during sum-
mer, decreasing during spring and showing their lowest
values during autumn, as it can be observed in Figure 3.
During summer 2012, all measured BTX showed their
highest concentrations during the midday (B2) decreas-
ing during the mornings and registering their lowest lev-
els during the afternoon (Figure 4). During summer 2012,
all the studied compounds registered their highest values
of concentration during the afternoon (B3), decreasing
during midday (B2) and showing their lowest values
during the mornings (B1) as it can be observed in Figure
5. In autumn 2012, Bz, EBz and p-X showed their highest
BTEXLEVELSDURINGTHESAMPLI NGPERIOD
0
10
20
30
40
50
60
70
80
90
100
B1 B2 B3 B1B2 B3 B1 B2 B3 B1 B2 B3
SAMPLINGPER IO D :B1:08:00‐09:30h,B2:13:00‐14:30h,B3:16:17:30h
Concentrations(ppbv)
MEAN MAXIMUM MINIMUM STAND ARD DEVIATION
BENZENE
ETHYLBENZE P‐XYLENE
TOLUENE
Figure 2. BTX diurnal variation in this study.
BTEXLEVELSSEASONALVARIA TI ON
0
5
10
15
20
25
30
35
40
45
50
SPSU AU SPSU AU SPSU AU SPSU AU
SAM PLI NG PERIOD:SP:Spring , SU:Summ er,AU:Autumn
Concentratio ns (ppbv)
MEAN MAXIMUM MINIMUM STANDARDDEVIATION
BENZENE
ETHYLB ENZ ENE
P‐XYLENE
TOLUENE
Figure 3. BTX Seasonal variation during this study.
Table 1. Comparison of atmospheric concentrations of BTX (ppbv) found in this study with data of other studies around the
world.
Location Bz T EBz p-X
Kocaely, Turkey (urban) [1] 0.7077 9.4277 2.2395 8.4919
Rome [16] 11.1167 26.4697 4.0552 12.460
Belgium (busy road) [17] 0.9614 1.9832 0.341 0.8959
Hong Kong (industrial) [18] 4.7191 36.9966 5.6864 6.4213
Izmir (urban) [19] 1.0365 4.0859 0.8409 1.7274
Fuji (industrial) [20] 0.645 3.7170 0.3502 0.4215
Pamplona (urban) [21] 0.8893 3.5204 0.4954 0.7785
Mexico City (urban) [8,22] 6.5447 [8] 31.647 [22] 4.3086 [8] 15.6848 [8]
This study (urban) 5.4233 11.2383 3.9722 8.3284
B
z: Benzene; T: Toluene; EBz: Ethylbenzene; p-X: p-Xylene.

Diurnal and Seasonal Variation of BTX in Ambient air of One Urban Site in Carmen City, Campeche, Mexico 43
BTEXLEVELSDURINGSPR I NG2012
0
10
20
30
40
50
60
70
80
90
100
B1 B2 B3B1B2B3 B1 B2B3 B1 B2 B3
SAMPLINGPER I OD :B1:08:00‐09:30h,B2:13:00‐14:30h,B3:16:17:30h
Concentrations(ppbv)
MEAN MAXIMUM MINIMUMSTAN DARDDEVIATION
BENZENE
ETHYLBENZENE P‐XYLENE
TOLUENE
Figure 4. Diurnal variation for BTX during spring 2012.
BTEXLEVELSDURINGSUMMER2012
0
5
10
15
20
25
30
35
40
45
B1B2 B3B1 B2B3 B1B2 B3B1 B2B3
SAMPLINGPER IO D :B1:08:00‐09:30h,B2:13:00‐14:30h,B3:16:17:30h
Concen t ra tio n s (ppbv)
MEAN MAXIMUM MINIMUM STANDA RDDEVIATION
BENZENE
ETHYLB ENZENE
P‐XYLENE
TOLUENE
Figure 5. Diurnal variation for BTX during summer 2012.
values during the afternoons (B3), decreasing during the
mornings (B1) and showing their lowest levels during the
midday (B2) as it can be observed in Figure 6.
3.2. Toluene to Benzene Ratio (T/Bz Ratio)
T/Bz ratio has been commonly used as an indicator of
traffic emissions. Bz and T are constituents of gasoline
and are emitted into the atmosphere by motor vehicle
exhausts. The toluene content of gasoline and motor ve-
hicle exhaust is 3 - 4 times higher than Bz content [16].
A value of around 2 - 3 is characteristic of vehicular
emissions in many urban areas worldwide [15,22,23].
The range for Carmen City in this study was between
2.45 and 2.8 being higher during autumn and lower for
sum- mer. Mean T/Bz ratios found were: 2.4526, 2.4762
and 2.8036 for spring, summer and autumn, respectively.
These values are agree with typical values of vehicular
emissions (2 - 3) reported for other urban areas, suggest-
ing that this site was under the influence of mobile
sources.
3.3. Pearson’s Correlation
Table 2 shows the Pearson’s correlation coefficient ma-
trix for the mean concentrations of BTX. A significant
correlation between Bz and T indicates that they were
possibly originated from vehicular emissions. EBz and
p-X had a good correlation, indicating that both com-
BTEXLEVELSDURINGAUTUMN2012
0
10
20
30
40
50
60
70
80
90
B1 B2 B3 B1B2 B3 B1 B2B3 B1B2 B3
SAMPLINGPE RI O D :B1:08:00‐09:30h,B2:13:00‐14:30h,B3:16:17:30h
Concentratio ns (ppbv)
MEAN MAXIMUM MINIMUM STANDARDDEVIATION
BENZENE
ETHYLBENZENE P‐XYLENE
TOLUENE
Figure 6. Diurnal variation for BTX during autumn 2012.
Table 2. Pearson’s correlation coefficient matrix for studied
BTX.
Bz Ebz p-X T
Bz 1 0.2193 0.6646 0.6648
Ebz 0.2193 1 0.7983 0.01682
p-X 0.6646 0.7983 1 0.1085
T 0.6648 0.01682 0.1085 1
Bz: Benzene; EBz: Ethylbenzene; p-X: p-Xylene; T: Toluene.
pounds probably had their origin from gasoline vehicles,
petroleum plants and gasoline stations. T had the lowest
coefficients in this work with EBz and p-X, suggesting
that T had other additional sources. According to the
USEPA SPECIATE [22] data base, T, EBz and p-X are
consistent with sources profiles given for “gasoline vehi-
cle emissions”.
3.4. Meteorological Analysis
BTX concentrations were correlated with meteorological
parameter at surface level and 24 h backward air masses
trajectories were calculated for maximum concentrations
events using the HYSPLIT model from NOAA at 500,
700 and 1000 masl. The backward trajectories analysis
helps to determine the origin of air masses and probable
location of sources for the measured pollutants.
During spring season, the highest concentrations for
all BTX were registered when wind blowed from E,
where an avenue with high vehicular traffic is located
being highest the BTX levels during the midday sam-
pling (B2) as it can be observed in Figures 7 and 10. In
summer (Figures 8 and 11), Bz and EBz showed the
highest values when wind blowed from E and NE. The
most important offshore platforms facilities of Mexico
are located at NE and N of the sampling site. p-X showed
their highest concentrations during summer when wind
prevailed blowing from NE (B1), SW (B2) and SE (B3).
A sour gas recompression station is located at the SW of
the sampling site. Local sources related to one building

Diurnal and Seasonal Variation of BTX in Ambient air of One Urban Site in Carmen City, Campeche, Mexico
44
construction are located at SE of the sampling site.
During autumn (Figures 9 and 12) mornings the high-
est levels for all BTX were registered when wind blowed
from NE. During the midday, the highest concentrations
for EBz and p-X were observed when wind blowed from
NE, from SE and from N for Bz and T, respectively. In
the autumn afternoons, Bz and T showed their highest
levels when wind blowed from N, and from SW an W for
p-X and EBz, respectively. The principal activities of this
urban area are located at W from the sampling period.
3.5. Principal Component Analysis (PCA)
A principal component analysis was carried out in order
to study patterns in a multivariate data set for the three
climatic seasons (spring, summer and autumn) and for
the three sampling periods (08:00-09:30 h; 13:00-14:30 h;
and 16:00-17:30 h). The PCA analysis was applied for
the BTEX concentrations (benzene, toluene, ethylben-
zene and p-xylene), meteorological parameters (tem-
perature: T, barometric pressure: P, relative humidity:
RH, wind direction: WD, and wind speed: WS). Figures
11-19 show the PCA loadings obtained for the morning,
Wind Direction Influence during Spring 2012
0
50
100
150
200
250
300
350
400
BZ
B1 T B1 Ebz B1 P-X B1 BZ B2 T B2 Ebz B2 P-X B2 BZ B3 T B3 Ebz B3 P-X B3
BTX -Sampling period
Concentrations (g/m3)
E
SE
S
NW
NE
3
Figure 7. Wind direction influence on BTX concentrations
during spring 2012.
Wind Direction Influence during Summer 2012
0
50
100
150
200
250
BZ
B1 T B1 Ebz B1 P-X B1 BZ B2 T B2 Ebz B2 P-X B2 BZ B3 T B3 Ebz B3 P-X B3
BTX-Sampling period
Concentrations (g/m3)
NE
E
SE
S
SW
W
NW
3
Figure 8. Wind direction influence on BTX concentrations
during summer 2012.
Wind Direction Influence during Autumn 2012
0
10
20
30
40
50
60
70
BZ
B1 T B1 Ebz B1 P-X B1 BZ B2 T B2 Ebz B2 P-X B2 BZ B3 T B3 Ebz B3 P-X B3
BTX-Sampling period
Concentrations (g/m3)
N
NE
E
SE
S
SW
W
3
Figure 9. Wind direction influence on BTX concentrations
during autumn 2012.
midday and afternoon sampling periods (B1, B2 and B3,
respectively) for the three climatic periods (spring, sum-
mer and autumn).
In Figure 13 it can be observed that there were some
associations among compounds: a positive correlation
among p-Xylene (p-X), Benzene (B), Ethylbenzene (Ebz)
and Toluene (T), suggesting that these compounds had
probably sources in common during the mornings of
spring season (B1). BTX concentrations showed a nega-
tive correlation with wind speed indicating that as wind
speed increases, BTX concentrations decreases due to a
dilution effect. BTX-temperature (T) correlation was not
important, suggesting that these compounds did not have
their origin in evaporative emissions from oil service
stations.
In Figure 14 it can be observed that there were some
associations among compounds during the mornings of
summer season: BTX concentrations had a negative cor-
relation with wind speed; it suggests that as wind speed
increases, BTX concentrations decreases, due to a dilu-
tion effect. Relative humidity (RH) showed a negative
correlation with BTX suggesting that this condition con-
tributed to remove the atmospheric pollutants by wet
deposition or condensation [25,26]. Benzene (B) and
p-Xylene (p-X) showed positive correlations with tem-
perature (T) indicating that at least partially, these com-
pounds had their origin in evaporative emissions. In gen-
eral, all measured BTX showed high positive correlations
between each other, suggesting that they could have the
same emissions sources (Figure 14).
In Figure 15 it can be observed that for the autumn
season during the morning sampling period (B1), BTX
showed good correlations between each other, indicating
that they probably had sources in common. BTX concen-
trations had a negative correlation with wind speed; it
suggests that as wind speed increases, BTX concentra-
tions decreases, due to a dilution effect. Relative humid-
ity (RH) showed a negative correlation with BTX

Diurnal and Seasonal Variation of BTX in Ambient air of One Urban Site in Carmen City, Campeche, Mexico
45
Figure 10. Air mass backward trajectory for a maximum BTX high concentrations event during spring (June 17, 2012).
Figure 11. Air mass backward trajectory for a maximum BTX high concentrations event during summer (September 16, 2012).
Figure 12. Air mass backward trajectory for a maximum BTX high concentrations event during autumn (October 6, 2012).

Diurnal and Seasonal Variation of BTX in Ambient air of One Urban Site in Carmen City, Campeche, Mexico
46
Figure 13. PCA for spring season during the morning sam-
pling period B1: 08:00-09:30 h.
Figure 14. PCA for summer season during the morning
sampling period B1: 08:00-09:30 h.
Figure 15. PCA for autumn season during the morning
sampling period B1: 08:00-09:30 h.
suggesting that this condition contributed to remove the
atmospheric pollutants by wet deposition or condensation
[25,26].
In Figure 16, it can be observed that BTX had positive
correlations between each other for spring during the
midday sampling period (B2: 13:00-14:30 h), suggesting
that these compounds had probably sources in common.
The dilution effect was evident due to a negative correla-
tion among wind speed and all BTX was observed. A
negative correlation among temperature and BTX was
observed indicating that all measured BTX had different
sources than those related to evaporative emissions.
In summer season during the midday sampling period
(B2: 13:00-14:30 h) (Figure 17), BTX correlated posi-
tively with temperature indicating that probably these
compounds had their origin in evaporative emissions.
BTX had negative correlation with wind speed (dilution
effect) and relative humidity, suggesting that high water
vapor concentrations found in air masses removes par-
tially the air pollutants by wet deposition or condensa-
tion.
In Figure 18 it can be observed that during autumn
season for the midday sampling period (B2: 13:00-14:30
h), BTX had mixed sources. Bz-T and Ebz-p-X showed
good correlations indicating that these pairs of com-
pounds probably had their origin in common sources.
Figure 16. PCA for spring season during the midday sam-
pling period B2: 13:00-14:30 h.
Figure 17. PCA for summer season during the midday
sampling period B2: 13:00-14:30 h.

Diurnal and Seasonal Variation of BTX in Ambient air of One Urban Site in Carmen City, Campeche, Mexico 47
Figure 18. PCA for autumn season during the midday sam-
pling period B2: 13:00-14:30 h.
Ebz and p-X had a moderate positive correlation with
temperature, suggesting that at least partially these com-
pounds could be originated from evaporative emissions.
All measured parameters showed for this period a nega-
tive correlation with wind speed (WS).
During spring season for the afternoon sampling pe-
riod (B3), Bz-Ebz-p-X, and T-p-X had good correlations
(Figure 19) indicating that these pair of compounds had
probably common sources. BTX did not have a good
correlation with temperature indicating that the contribu-
tion of evaporative sources was negligible.
In summer during the afternoon sampling period: B3
(Figure 20), T had high correlations with Ebz and p-X,
suggesting that they had probably common sources. T
had a moderate positive correlation with temperature,
suggesting that this compound probably had its origin in
evaporative emissions. All measured parameters had a
negative correlation with wind speed (WS) and relative
humidity (HR) indicating the influence of dilution and
wet deposition/condensation processes.
In Figure 21 it can be observed that during the autumn
season for the afternoon sampling period (B3: 16:00-
17:30 h) BTX correlated positively, it indicates that these
compounds probably had their origin in the same sources.
All measures BTX showed a negative correlation with
wind speed and temperature for this period.
4. Conclusions
BTX concentrations in this work showed values compa-
rable to those reported for cities like Mexico and Hong
Kong. There was a clear diurnal pattern in the BTX con-
centrations, showing the highest levels during midday
(B2). BTX seasonal variation levels had a clear behavior
too, showing the highest concentrations during summer,
decreasing during spring and registering the lowest val-
ues during autumn. It is more probable than during sum-
mer that BTX could be originated from photochemical
Figure 19. PCA for spring season during the afternoon sam-
pling period B3: 16:00-17:30 h.
Figure 20. PCA for summer season during the afternoon
sampling period B3: 16:00-17:30 h.
Figure 21. PCA for autumn season during the afternoon
sampling period B3: 16:00-17:30 h.
reactions and evaporative emissions from gas and gaso-
line storage stations. BTX in this city had mixed sources
during the sampling period. According to T/Bz ratios and
the meteorological analysis, it was clearly under the in-
fluence of vehicular sources circulating in avenues located

Diurnal and Seasonal Variation of BTX in Ambient air of One Urban Site in Carmen City, Campeche, Mexico
48
at E of the sampling site. On the other hand, the wind
direction study showed that this site was under the influ-
ence of sources related to oil industry located at N, NE
and SW of the sampling site. We can therefore conclude
that air quality in this city is already a problem to con-
cern and it is necessary to establish air pollutants control
strategies. However, it is necessary to carry out intensive
monitoring campaigns in this site including criteria pol-
lutants (Ozone, NOx, NO2, CO, SO2) monitoring in order
to get more information about the origin of BTX.
5. Acknowledgements
The authors thank Universidad Autónoma del Carmen
for financial support of this work and Universidad
Autónoma de Nuevo León for technical support.
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