Journal of Environmental Protection, 2013, 4, 50-56
http://dx.doi.org/10.4236/jep.2013.48A1007 Published Online August 2013 (http://www.scirp.org/journal/jep)
Chemical Composition, Fluxes and Seasonal Variation
of Acid Deposition in Carmen Island, Campeche,
Mexico
R. M. Cerón1*, J. G. Cerón1, C. G. Carballo1, C. A. Aguilar1, C. Montalvo1, J. A. Benítez2,
Y. J. Villareal1, M. M. Gómez1
1Research Center on Environmental Sciences, Autonomous University of Carmen, Carmen City, Mexico; 2EPOMEX Institute,
Autonomous University of Campeche, San Francisco de Campeche, Mexico.
Received June 13th, 2013; revised July 13th, 2013; accepted July 30th, 2013
Copyright © 2013 R. M. 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
Two hundred and seven rain events from April to October 2012 were collected in Carmen Island, Campeche, Mexico,
and the concentration of 8 major ions with the pH of the rainwater was analyzed. Chemical composition variations as a
result of seasonal patterns, meteorological conditions, and mixed local and regional sources contribution were assessed.
In spite of the fact that nitrate and sulfate levels were higher than background hemispheric values, the average pH val-
ues were almost neutral. Carmen Island was under the influence of both, local and long-range transported emissions.
Chemical composition showed a dilution effect as a result of the monthly rainfall amount. Ca2+ and Na+ were the most
abundant ions, and these ions acted as acid neutralizers and buffered the acidity of the rain, suggesting that marine and
crustal aerosols played an important role in the acid-base interactions. Wet deposition fluxes obtained were compared
with reference values proposed as critical loads, fluxes obtained in this study did not exceed the critical values reported
for sensitive ecosystems in Europe, indicating that this site has yet enough capacity to support acidity, nitrogen and sul-
fur deposition. However, it is necessary to obtain reference values characteristics for tropical regions.
Keywords: Trace Elements; Acid Deposition; Deposition Fluxes; Critical Loads; Acid Rain; Campeche; Mexico
1. Introduction
Acid rain has been one of the most serious environmental
problems in many locations of the world. Atmospheric
constituents, and thus pollutant emissions, reach the sur-
face of the Earth by two main processes: 1) atmospheric
mechanisms in which precipitation is involved that con-
tribute to wet deposition; 2) processes prevailing during
dry periods that involve sedimentation, diffusion, impac-
tation and interception that contribute to dry deposition. In
spite of the fact that the chemical composition of wet
deposition has been largely studied over the last twenty
years in many places around the world, to determine the
real effect of acid deposition on ecosystems it is necessary
not only to know the ionic levels present in rainwater, it is
also required to estimate the deposition fluxes, and the ex-
ceedances to the reference values proposed as critical
loads for a specific region [1].
Wet deposition is important in coastal zones because of
its episodic nature and partial transference in solution to
receptors, enhancing biological interactions. Acid com-
ponents and trace metals present in wet deposition may
cause an eventual significant damage to the ecosystems.
In Mexico, only a few studies about rainwater chemical
composition have been carried out, studies about wet
deposition fluxes are scarce and critical loads data are not
available [2].
Potential ecological effects of acid deposition in tropi-
cal environments remain uncertain, therefore, qualitative
and quantitative systematic assessments are required to
determine when critical loads are exceeded, to diagnose
the state of perturbation of natural sites, to assess annual
trends, deposition patterns and ecosystem responses.
This study establish a solid outline of the main chemical
characteristics of wet deposition in order to estimate
critical loads exceedances and the potential ecological
effects related with acid deposition in a Natural Area
*Corresponding author.

Chemical Composition, Fluxes and Seasonal Variation of Acid Deposition in Carmen Island, Campeche, Mexico 51
Protected in Campeche, Mexico.
2. Material and Methods
2.1. Site Description
This study was conducted in Carmen Island, Campeche,
Mexico within the Protected Natural Area named “Laguna
de Términos”. Climate in the site is sub-humid warm with
rains occurring along the summer. The average annual
rainfall is 1300 mm and the mean annual temperature is
27˚C. Prevailing winds blow from NE (from September to
March) when the site is under the influence of cold fronts
named “Nortes” and from SE during the rest of the year
(from April to August) when the site is under the influence
of tradewinds. Site is under the influence of maritime air,
land and sea-breezes all year.
2.2. Sampling Method
Rain samples were collected from April to October 2012
by using an automated wet-dry deposition collector (Tisch
Environmental Inc) located on the roof (at 3 m above the
ground) of the Building of the Department of Chemical
Engineering at Autonomous University of Carmen in
Campeche, Mexico (Figure 1).
Sampler has two buckets to collect wet and dry depo-
sition respectively. Collection buckets were washed and
rinsed thoroughly with deionized water several times
before sampling. Sampler has an automated lid operated
by a humid sensor which moves depending on the begin-
ning or the end of the rain event, assuring that only rain-
water is collected in the wet bucket during rain events.
Samples were collected in a daily basis and a rain gauge
registered the precipitation amount daily. Those rain
events with volume collected lower than 250 ml were
neglected since samples were not enough for the chemi-
cal analysis.
Sampling site
18°38’48.28”N y91°49’0.73”W
Grades
Figure 1. Location of the sampling site.
pH and conductivity were measured in site by using a
precision pH meter (TERMO ORION 290) and a con-
ductivity meter (CL 135), respectively. Surface meteoro-
logical data were obtained from a portable meteorologi-
cal station (Davies Inc) operating during the whole study
period.
2.3. Analytical Method
The rain samples were filtered through 0.45 µm Millipore
membrane filters and stored at 4˚C until analysis.
2
4
SO

was analyzed by turbidimetric method [3] 3 NO

was determined by colorimetric method [4], and Cl− was
analyzed according to NMX-AA-073-SCFI-2001 [5].
Cations (Na+, K+, Ca2+ and Mg2+) were analyzed by
Atomic Absorption Spectroscopy (Thermoscientific ice
3000) with the Flame Technique according to EPA
methods [6-9]. Ammonium was determined by molecular
absorption spectrometry using the indophenol-blue me-
thod.
Repeatability was determined by analysis of samples
from at least three replicate measurements. The quality
assurance was routinely carried out by using ionic balance.
The relative standard deviation was less than 5% for re-
producibility test
2.4. Meteorological Analysis
Wind roses were constructed for each rain event with
WRPLOT VIEW 6.5.2 (Lakes Environmental, 2011) To
trace the origin of the air masses during the study period,
backward air mass trajectories were calculated for all rain
events by using HYSPLIT (Hybrid Single Particle La-
grangian Integrated) from NOAA (US National Oceanic
and Atmospheric Administration).
2.5. Statistical Analysis
Pearson’s correlation analysis was applied to test the
relationship among the total trace element concentrations.
Factor analysis was applied to determine the factors un-
derlying the interactions among the surveyed species.
ANOVA was performed to test the differences between
each element. Principal components analysis (PCA) was
used to visualize the relationship among trace elements
focusing on the inter-element correlation coefficients.
3. Results
3.1. Ionic Concentrations
To assure the reliability of these data and to find the pos-
sibility of the presence of other ions such as 3 HCO

and
2
3
CO

, the ionic balance was checked out. Ionic balance
obtained was acceptable, the observed ratio of cations to
anions in this study was within the acceptable range, in-
dicating that the most of ions present in rainwater samples

Chemical Composition, Fluxes and Seasonal Variation of Acid Deposition in Carmen Island, Campeche, Mexico
52
were analyzed.
Figure 2 shows the concentrations of the major ions in
rain samples collected during 2012 in Carmen Island.
The concentrations of the major ionic species were in the
following order (Figure 3):
22 2
43 4
CaNa SONOMgKNH Cl
  
 

Sulfate levels (86.19 µEq·l−1) exceeded almost eight
times the background hemispheric values reported by
Galloway et al. [10] for remote sites.
In addition, nitrate levels (33.94 µEq·l−1) exceeded
twelve times the reference values for clean atmospheres
[10] This fact suggests that there was an evident anthro-
pogenic influence from both, local and regional sources.
Calcium and sodium were the most abundant ions,
suggesting a significant contribution from marine aerosol
and crustal. Ammonium ion was the least abundant; it is
agree with the main economical activities in the island,
Figure 2. Concentrations of the major ions in rainwater
collected in Carmen Island, Campeche, Mexico.
Figure 3. Ionic abundance for rain samples collected in
Carmen Island, Campeche, Mexico.
since agriculture is not developed in this site. Sulfate
levels were higher than nitrate, indicating that this site
was under the influence of regional sources.
3.2. Acidity of Precipitation
Figure 4 shows the frequency distribution of pH in Car-
men Island during 2012. From Figures 4 and 5, an evident
seasonal pattern was observed in pH, values are higher
when rainfall increases, whereas pH decreases during the
dry season (April, May). The highest values were ob-
served during August, when hurricane “Ernesto” arrived
to the island. It is agree with reported by Padilla et al. [11],
where a relationship between hurricanes (“Paulina” and
“Nora”) and high pH levels was reported.
During the occurrence of hurricanes, coastal sites are
under the influence of tropical maritime air that brings
high amounts of sea salt that contribute to pH and sodium
levels.
Figure 4. Monthly var i ation of pH in precipitation.
Figure 5. Monthly variation of rainfall and pH in rainwater
samples collected in Carmen Island.

Chemical Composition, Fluxes and Seasonal Variation of Acid Deposition in Carmen Island, Campeche, Mexico 53
pH ranged from 2.02 to 7.18, with an average value of
5.69. 38.98% of the total rain events measured had pH
values less than 5, 3.39% of the total samples had pH
values between 5 and 5.6, and 57.63% had pH values
higher than 5.6.
3.3. Dilution Effect of Rainwater on Chemistry
Composition
From Figures 4 and 5, it can be observed that pH de-
creased during September and October, just when prevail
wind direction shift from SE to NE, during this period
the site is under the influence of cold fronts that promote
the long-range transport from sources located at NE from
Carmen Island (gas and oil offshore platforms located at
Gulf of Mexico, where gases and particles released could
produce secondary aerosols which probably were up
taken to the rainwater by heterogeneous nucleation, rain-
out and wash-out processes, resulting in lower pH val-
ues).
In contrast, during August, the site was subjected to
tradewinds (from SE) that promoted the uptake of crustal
particles from the Yucatan Peninsula, where soils are
mainly calcisols, contributing to the neutralization proc-
ess and resulting in higher pH levels.
The observed ionic concentrations showed a decreas-
ing trend with increasing precipitation amount (Figures 6
and 7); it suggests that rainwater had a dilution effect on
precipitation chemistry. Precipitation chemistry may also
be partially dependent on the residence time of floating
particles in the air [12].
During dry season, particles persist in the air for long
periods, thereby accumulating to relatively high levels,
whereas during the plenitude of the wet season where
rain events with high amounts of rainfall are frequent,
pollutants and aerosols in the atmosphere are under the
influence of scavenging processes, thereby minimizing
ion concentrations in rainwater.
Figure 6. Relationship between rainfall amount and cation
concentrations.
Figure 7. Relationship between rainfall amount and anion
concentrations.
3.4. Temporal Trends
From Figures 8 and 9, it can be observed that nitrate and
sulfate levels were higher during the wet season, sug-
gesting that besides of local sources, regional sources
could contribute with significant amounts of precursor
gases of acid rain.
A good relationship between nitrate and sulfate was
observed (Figure 8), being sulfate levels higher than
nitrate. It suggests that these ions had a common regional
source: sour gas flares from offshore platforms located at
NE from this site. In spite of ammonium levels were low;
from Figure 9 it can be observed a similar trend between
nitrate and ammonium, suggesting that probably these
ions had a common local source: vehicular emissions.
3.5. Inter-Elemental Relationships
To investigate and get a quick overview on the possible
source of ions, the correlation analysis was applied and
the correlation matrix for the ion pairs is presented in
Table 1.
The highest correlation appeared for K+-Ca2+, Ca2+-
Mg2+, suggesting that these ionic species had a common
origin in marine aerosol and crustal particles. 2
4
K-SO

,
2
44
N
H-SO

 and 3
K-NO

 were good correlated. These
ion pairs probably occurred in precipitation as a result of
atmospheric chemical reactions [13].
Some base ions commonly found in precipitation acts
as buffers for the acidity of rainwater. To estimate the
neutralization capacity of each alkaline compound, the
neutralization factors (NF) were calculated.
To verify which cation (Na+, Mg2+, Ca2+) more fre-
quently neutralized the acidic components in rainwater, a
triangular diagram was drawn, showing the relative pro-
portion of these three elements (Fi gure 10).
Calcium and sodium were the most abundant ions in
rainwater samples, and the contribution of marine aerosol

Chemical Composition, Fluxes and Seasonal Variation of Acid Deposition in Carmen Island, Campeche, Mexico
54
Figure 8. Temporal trends in sulfate, nitrate and pH levels in rainwater.
Figure 9. Temporal trends in nitrate and ammonium levels in rainwater.

Chemical Composition, Fluxes and Seasonal Variation of Acid Deposition in Carmen Island, Campeche, Mexico 55
Table 1. Matrix of Pearson rank correlation coefficients for major ions.
K Na Ca Mg NH4 Cl NO3 SO4
K 1
Na 0.39 1
Ca 0.45 0.18 1
Mg 0.31 0.22 0.46 1
NH4 0.37 0.02 0.09 0.04 1
Cl 0.21 0.03 0.16 0.17 0.16 1
NO3 0.41 0.12 0.08 0.08 0.22 0.43 1
SO4 0.62 0.48 0.34 0.41 0.54 0.001 0.08 1
Figure 10. Triangular diagram of NF of predominant alka-
line ions.
(as a result of breezes and transported maritime air
masses) and crustal dust (since Carmen Island had a
sedimentary origin where calcisols are dominant soil type)
as a result of the prevailing meteorology was completely
evident. It means that crustal and sea salt aerosols played
an important role in the neutralization process.
3.6. Wet Deposition Fluxes
In spite of pH levels were almost neutral, nitrate and sul-
fate levels exceeded the hemispheric values reported for
remote and clean atmospheres. Therefore, to estimate the
real effect of atmospheric pollution on Carmen Island
ecosystems, it was necessary to calculate the wet deposi-
tion fluxes.
Critical load is defined as the amount of chemical
compound that one ecosystem can tolerate without suffer
damages. To obtain a diagnosis of the vulnerability of the
ecosystems it is necessary to compare deposition fluxes
with reference values proposed as critical load in a spe-
cific region, these values are commonly reported for soils,
fresh waters or sensitive species of vegetation o fauna. In
Mexico, critical load data are not available, therefore, in
this work; data obtained were compared with data reported
in Europe [14]: 5 kg·N·ha−1·yr−1 and 3 kg·S·ha−1·yr−1.
Nitrogen and sulfur deposition fluxes in Carmen Island
were 0.15 and 0.29 kg·ha−1·yr−1. In both cases, fluxes did
not exceed the reference values reported for sensitive
ecosystems in Europe.
However, it is necessary to estimate critical loads in
this specific site, since deposition patterns, prevailing
sensitive species, and ecosystem responses may be dif-
ferent in tropical sites than in temperate regions at
mid-latitudes.
From Figure 11, it can be observed that K+, Na+, Ca2+,
3
NO

and 2
4
SO

showed the highest fluxes, suggesting
that mixed local and regional sources contributed in a
significant way to deposition process.
4. Conclusions
The analysis of the rain samples collected during 2012 in
Carmen Island, Campeche, Mexico showed that:
1) The scavenging of pollutant and geochemical aero-
sols from the air, and prevailing meteorological conditions
affected directly and greatly the pH and chemical com-
position of the rainwater in this site.
2) The major ions and their concentrations in rainwater
followed the order of:
22 2
43 4
CaNaSO NOMgKNHCl

 
  

3) 3 NO

and 2
4
SO

were the major acidifying ions in
rainwater, whereas Ca2+ and Na+ were the predominant
basic ions in buffering and neutralizing the acidity in
rainwater. Crustal and sea salt aerosols played an impor-
tant role in buffering rainwater acidity.

Chemical Composition, Fluxes and Seasonal Variation of Acid Deposition in Carmen Island, Campeche, Mexico
56
Figure 11. Wet deposition fluxes during 2012 for Carmen
Island, Campeche, Mexico.
4) In spite of nitrate and sulfate levels were high and
exceeded the hemispheric values reported for clean at-
mospheres, deposition fluxes did not exceed the critical
loads reported for sensitive ecosystems in Europe.
5) It is necessary to estimate reference values of critical
loads to obtain an exact diagnostic of the vulnerability of
the ecosystems to current deposition fluxes of acidity,
nitrogen and sulfur in this region
5. Acknowledgements
This work was financially supported by University Fund
UNACAR-CAIPI-DACQYP/2012-02.
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