Aerosol and Air Quality Research, 12: 856–878, 2012
Copyright © Taiwan Association for Aerosol Research
ISSN: 1680-8584 print / 2071-1409 online
doi: 10.4209/aaqr.2012.03.0068
Air Masses and Weather Types: A Useful Tool for Characterizing Precipitation
Chemistry and Wet Deposition
A.I. Calvo1*, V. Pont2, F.J. Olmo3,4, A. Castro5, L. Alados-Arboledas3,4, A.M. Vicente1,
M. Fernández-Raga5, R. Fraile5
1
Centre for Environmental and Marine Studies (CESAM), University of Aveiro, Aveiro 3810-193, Portugal
Laboratoire d’Aérologie /OMP, UMR 5560, Université de Toulouse III, CNRS-UPS, 14, av. E. Belin, Toulouse 31400,
France
3
Atmospheric Physics Group, CEAMA, University of Granada. Junta de Andalucía, Granada 18006, Spain
4
Department of Applied Physics. University of Granada, Granada 18071, Spain
5
Department of Physics, IMARENAB, University of León, León 24071, Spain
2
ABSTRACT
This study is an analysis of 344 days with rainfall recorded during five years in a remote regional background EMEP
(Cooperative Programme for the Monitoring and Evaluation of the Long Range Transmission of Air Pollutants in Europe)
station in Spain. The chemical composition of the rainwater associated with air masses (nine categories) and weather types
(26 categories) was characterized. The chemical composition of rainwater was dominated by calcium (Ca2+) and sulphate
(SO42−-S), with VWM (Volume Weighted Mean) during the period studied (2002–2006), with 55 μeq/L and 34 μeqS/L,
respectively. Calcium, sodium (Na+), ammonium (NH4+-N) and magnesium (Mg2+) seem to be dominant components in
the neutralization of the rainwater. By applying Pearson correlations, principal component analysis and enrichment factors,
it is possible to identify source types for the precipitation constituents. Interannual and intra-annual variability was also
been studied. High calcium levels are associated with the frequent intrusions of Saharan dust that occur during the summer,
and the maximums of chlorine and sodium in the winter may be due to the greater amount of maritime air recorded during
this season. Wet deposition was determined by focusing on nitrogen deposition, registering mean annual values of 155
mgN/m2/year (from the NO3−-N) and 165 mgN/m2/year (from the NH4+-N).
Keywords: Rainwater chemical composition; Trajectory analysis; Circulation weather types; N deposition; Wet deposition.
INTRODUCTION
Rain acts as a powerful mechanism to remove pollutants
from the atmosphere. Precipitation chemistry is the result of
a series of in-cloud and below-cloud atmospheric chemical
reactions and a complex interaction between microphysical
processes and cloud dynamics (Mouli et al., 2005). The
importance of studing chemical composition of rainwater
focus on several aspects: i) it is a valuable tool that helps us
to identify the pollutant sources involved in this composition;
ii) it provides information on the transportation and
dispersion of pollution; iii) it is involved in problems related
to acid deposition, eutrophication, trace metal deposition,
biogeochemical cycling, ecosystem health and global climate
change and iv) it is a very useful tool for validating model
*
Corresponding author. Tel.: +351 324 370 200;
Fax: +351 234 370 309
E-mail address: [email protected]
simulations of air pollution (Zunckel et al., 2003; Sanets and
Chuduk, 2005; Brimblecombe et al., 2007; Zhang et al.,
2007; WMO, 2008; Budhavant et al., 2009; Galy-Lacaux
et al., 2009; Yi et al., 2010).
Due to its crucial importance, precipitation composition
has been and is systematically studied all over the world
(e.g. Tanner, 1999; Herut et al., 2000; Okai et al., 2002;
Zhang et al., 2007; Celle-Jeaton et al., 2009; Galy-Lacaux et
al., 2009; Huang et al., 2009; Beem et al., 2010; Calvo et
al., 2010; Das et al., 2010a, b; Osada et al., 2011). Aerosols
and gases released into the atmosphere can be transported
over long distance from their source, and can be removed
by dry or wet deposition (e.g. Fraile et al., 2006; Shen et
al., 2011). Background levels, established for remote areas
far from the direct impact of anthropogenic sources, provide
relevant information mainly because it allows us to
determine the extent of anthropogenic pollution as well as
to address the potential influence of long-range transport to
rural areas. Networks of wet deposition are very useful to
establish appropriate thresholds (Das et al., 2010a) for
policy decisions. Among the several extensive networks of
Calvo et al., Aerosol and Air Quality Research, 12: 856–878, 2012
wet deposition in operation in different places around the
world (Japan Environmental Agency (JEA) Network, East
Asian Network (EANET), National Atmospheric Deposition
Program (NADP- in North America), etc.), Europe has the
European Monitoring and Evaluation Program (EMEP).
The EMEP network consists of 150 stations distributed in
35 countries throughout the whole of the European continent.
Reports with information on emissions, concentrations and
depositions of air pollutants, transboundary fluxes,
exceedances to critical loads and threshold levels, etc. are
frequently published (EMEP, 2012). These reports show
that transboundary transport is responsible for a significant
fraction of the pollution in European cities, as well as in
rural areas (e.g., EMEP-WMO, 1999). Thus, for example,
Krzyzanowski, (1999) pointed out that as much as 40–60%
of PM10 levels may be attributable to long-range transport
in many populated areas, mainly in places where there are
no heavily polluting local sources of PM. The study carried
out by Kindap et al. (2006) in Istanbul showed that transboundary sources may be responsible for as much as half
of the background PM10. Hacisalihoglu et al. (1992) in
their study near the Black Sea, found that 70% of the mean
concentrations of various pollutants were originated from
Central and Western Europe.
Ten EMEP stations are currently operative in Spain,
distributed all over the country (EMEP, 2012).
Among the different species present in rainwater, the
deposition of atmospheric nitrogen (NOX, NHY) has an
important relevance due to its large influence on terrestrial
and aquatic ecosystem. Thus, an excessive input of reactive N
could cause important an numerous ecological perturbations
(Matson et al., 2002; Yu et al., 2011) such as decrease of
plant diversity (Bobbink et al., 2010; Stevens et al., 2010),
eutrophication of surface waters (Bencs et al., 2009; Rojas
and Venegas, 2009), or changes of greenhouse gas flux
(Jiang et al., 2010; Li et al., 2012).
It is important to mention that, at global scale, reactive
N has increased from 15 Tg N in 1860 to 187 Tg N in 2005
(Galloway et al., 2008) and, according to recent studies
(Nakicenovic and Swart, 2000; Galloway et al., 2004;
Lamarque et al., 2005), the increasing trend is considered to
be enhanced in the next few decades. Trends of monitored
nitrogen in Europe have been studied by several authors
(Sopauskiene et al., 2001; Puxbaum et al., 2002; EMEP,
2004a, b; Honová et al., 2004; Fowler et al., 2005), and
they conclude that, in many countries, a large part of the
nitrogen is emitted by sources outside the countries where
the measurement sites were situated, so transboundary fluxes
need to be taken into account (Fagerli and Aas, 2008).
Current and future (2030) deposition of reactive nitrogen
to land and ocean surfaces has been estimated by Detener et
al. (2006) by using several atmospheric chemistry transport
models. They concluded that the main factor conditioning
future deposition fluxes will be changes in emissions,
whereas changes in atmospheric chemistry and climate will
have a lower influence. Thus, it is important to identify the
main sources of reactive nitrogen in order to control them
and enforce current air quality legislaton, avoiding future
important problems (e.g., eutrophying and acidifying
857
deposition of the ecosystems, air quality or radiative forcing)
(Detener et al., 2005, 2006; Shindell et al., 2006; Stevenson
et al., 2006).
This study provides an analysis of 344 days with rainfall
recorded between 1 January 2002 and 31 December 2006
in a remote regional background EMEP station in Víznar,
Granada, Spain. The chemical composition of the rainwater
associated with air masses and circulation weather types
(CWT) has been established. Furthermore, by applying
various statistical techniques it has been possible to identify
data relationships and source types for precipitation
constituents. Special attention has been focused on nitrogen
deposition. These results significantly contribute to the
knowledge on rainwater quality in background stations in
Europe, and point out the relevance of long range transport
on atmospheric pollution.
STUDY ZONE
The measurements were made in Víznar (37°14'N,
03°28'W; 1260 m a.s.l), a rural area located 12.5 km NE of
the city of Granada, in the south-east of Spain (Fig. 1). It is
situated on one of the mountains that surround the basin of
Granada, which form a part of the Sierra de Huetor Natural
Park, a mountainous region of medium height with large
masses of holm oaks (Quercus ilex) and Portuguese oaks
(Quercus faginea). The geological setting embraces the
Alpujarride complex, with its carbonate rocks, the Malaguide
complex, of a detritic character, and the Subbetic Domain,
with an essentially carbonate nature (Rubio et al., 2008).
In order to find low emission densities in the vicinity of
EMEP sites, there is a general tendency to locate EMEP
sites at higher altitudes; criterion which can more easily be
met in mountainous areas (Spangl et al., 2007; EC, 2011).
In Víznar the land use is distributed as follows: 1% urban
area, 17% coniferous trees, 37% bushes, 42% cereals and
3% paved roads (EMEP, 2012).
The climate is of the Continental Mediterranean type,
characterized by cold winters, with many severe frosts,
while the summers are very warm (www.aemet.es). The
mean annual temperature is 13°C. The annual precipitation is
around 400 mm (Spanish National Institute of Meteorology,
AEMET). March is the month with the highest rain rate
(444 mm), and July and August with the lowest, with 3.3
and 4.3 mm, respectively. More detailed information about
this study zone has been reported by Calvo et al. (2010).
MATERIALS AND METHODS
Sampling and Analysis Methodology
Wet deposition samples were collected at the Viznar
EMEP station between 1 January 2002 and 31 December
2006, with a total of 344 samples on a daily basis. Integrated
samples were collected daily at 0700 UTC and stored in a
refrigerator until they were sent, once a week, to the
laboratory at the Carlos III Health Institute in Madrid,
Spain. Rain samples were analysed in order to obtain the
concentration of sodium, magnesium, calcium, chloride,
potassium (all in μeq/L), sulphate (μeqS/L), nitrate (μeqN/L),
Calvo et al., Aerosol and Air Quality Research, 12: 856–878, 2012
858
Fig. 1. Study zone (Víznar) in the province of Granada (Spain).
ammonium (μeqN/L), conductivity (μS/cm) and pH (EMEP,
2012).
Potassium, sodium, magnesium and calcium were
determined using Atomic Absorption or Emission
Spectrophotometer and ammonium concentrations were
measured by means of the Spectrophotometric Indophenol
method. Ionic chromatography was used in order to
determinate sulphate, nitrate and chloride concentrations.
Selection criteria, sampling procedures, analysis and data
quality controls are pre-established (EMEP, 2000, 2001) as
Viznar is an EMEP station.
Volumetric Mean
The volumetric mean (VWM) -in μeq/L- and the standard
deviation of the volumetric mean (VWSD) have been
calculated. The following equations have been used to
calculate these two parameters (Galloway and Gaudry, 1984):
N
C P
i i
VWN =
i=1
N
(1)
 Pi
i=1
12
2
N
 N
 N
 
2
  Pi  C i Pi    Ci Pi  
 i=1
 
VWSD =  i=1 i=1
2 N


N


2


P
P


i


i
 i=1  i=1


(2)
where Ci represents the concentration of a specific element
in our sample (in μeq/L except for the pH and conductivity
–μS/cm), Pi is the amount of precipitation recorded for
each event (in millimetres) and N is the number of samples.
Using the VWM, we calculated the concentration of an ion
in a given period (one month, one year, etc.), as a result of
which we take into account the influence of the amount of
rainfall on the concentration of ions (Staelens et al., 2005).
Enrichment Factors
Enrichment factors (EnF) have been calculated, both for
the seawater and for the crustal material (Zhang et al., 2007;
Huang et al., 2008), according to the following equation:
EnF = (Cx/Cr)sample/(Cx/Cr)crustal or seawater
(3)
where (Cx/Cr)sample is the quotient of the concentration of
an element (x) with respect to a reference element (r) in the
sample, and (Cx/Cr)crustal or seawater is the same quotient
considering the concentrations in the crustal material or
seawater.
In our study, we used sodium as a reference element of
marine origin, and calcium as a reference element of crustal
origin. Following Jordan et al. (2003), Mg2+ vs. Na+ have
been plotted and sizing by Ca2+ (Fig. 2) As indicated by
Jordan et al. (2003), it is possible to determine which species
to use as the reference sea-salt species by comparing the
measured ratio of Mg2+/Na+ to the equivalence ratio of
0.227 found in bulk seawater (Wilson, 1975; Keene et al.,
1986). A ratio in excess of 0.227 indicates a crustal Mg2+
influence, while a ratio less than this suggests a crustal Na+
component. In this study, Mg2+ is clearly enhanced, altering
the slope significantly from what one would expect for sea
salt. Regarding Ca2+, high values of Mg2+ are linked to high
values of Ca2+, indicating a similar temporal variation. The
smaller points (lower Ca2+ concentration) are closer to Mg2+
-Na+ seawater points. Thus for this study, Na+ is used as the
reference species for sea salt, since it appears less likely to
suffer from major deviations from the marine source.
The quotients of the concentrations of the different
elements in seawater (Cx/CNa) and crustal material (Cx/CCa)
were obtained based on the studies of Keene et al. (1986)
and Taylor (1964), respectively.
Elements with values higher than 10 are assumed to come
from other sources apart from the crustal or marine source,
for EnFcrustal and EnFseawater respectively (Báez et al., 2007).
Estimates of Neutralisation in Precipitations
Inorganic (H2SO4 and HNO3) and organic acids (mainly
formic, acetic and oxalic acids) are involved in the
Calvo et al., Aerosol and Air Quality Research, 12: 856–878, 2012
300
Samples
Seawater
250
Mg2+ ( eq L -1)
859
200
150
100
50
0
0
50
100
150
+
200
250
300
-1
Na ( eq L )
2+
+
Fig. 2. Mg versus Na . Points are sized by Ca2+ concentration.
precipitation acidity (Keene et al., 1988; Sanhueza et al.,
1992; Peña et al., 2002; Tanner and Law, 2003; Wang et al.,
2007; Xu et al., 2010; Zhang et al., 2010). Sources of these
acids include both anthropogenic and biogenic emissions.
Biomass burning, soil, traffic, vegetation, in-cloud process
or oxidation from precursor compounds in the gas phase
have been identified such as possible sources (Kawamura
et al., 1985; Keene and Galloway, 1988; Talbot et al., 1988;
Grosjean, 1989; Avery et al., 1991; Gradel and Crutzen,
1993; Willey and Wilson, 1993; Kumar et al., 1996; Guenther
et al., 2006; Prakash and Kumar, 2010; Zhang et al., 2011).
It has been estimated that organic acids contribute between
25% and 65% of the rainwater acidity in industrial and urban
areas (Yu et al., 1998; Altieri, 2009) and this contribution
is higher in remote areas (Galloway et al., 1982, Likens et
al., 1987, Andreae et al., 1988; Yu et al., 2009).
Due to the lack of organic acid concentrations,
neutralization factors have been calculated only considering
SO42− and NO3−, following Kulshrestha et al. (1995)
expression:
NFX =
X
2
4
SO + NO3
(4)
where X is the alkaline component (Ca2+, NH4+, Na+, Mg2+)
with all of the ions expressed as μeq/L.
Statistical Procedures
Principal Components Factor Analysis (PCA) was applied
in order to explore data relationships and source types for
precipitation constituents. This multivariate statistical method
allows to reduce a multidimensional system with many
correlated variables into a simpler system of uncorrelated
variables, called principal components, which explain a high
percentage of variance of the original system (Calvo et al.,
2010). By means of the correlation of the variables to the
factors, it is possible to interpret the factors obtained and to
identify the potential source of variance associated with
each factor (Drever, 1982).
Correlation analysis has been applied in order to examine
the relationships between the ions analysed.
Trajectories
Five days long back-trajectories for three different
altitudes -500 m, 1500 m and 3000 m a.g.l.- calculated
with the HYSPLIT model -Draxler and Rolph (2003)-,
using the FNL (Final analysis) database, were used in order
to study the influence of different air masses on the
chemical precipitation in our study zone. The precipitation
events were classified into nine groups (Mediterranean,
Tropical Maritime, Polar Maritime, Local, Continental,
Arctic, Saharan 500 m, Saharan 1500 m and Saharan 3000 m)
following the methodology described by Calvo et al. (2008,
2010). Saharan category has been segregated into three
altitudes aiming to reveal the influence of Saharan air masses
at high levels on rainwater chemical composition (Fig. 3).
A detailed description of the methodology carried out
for the air masses classification can be found in Segura et
al. (2012).
Circulation Weather Types
A Circulation Weather Types (CWTs) classification was
carried out based on Jenkinson and Collison (1977) and
Jones et al. (1993), in order to identify the type of weather
associated with a particular synoptic situation. The daily
circulation affecting the Iberian Peninsula is described
using a set of indices associated with the direction and
vorticity of the geostrophic flow. The indices used were the
following: southerly flow (SF), westerly flow (WF), total
flow (F), southerly shear vorticity (ZS), westerly shear
vorticity (ZW) and total shear vorticity (Z). These indices
are computed using sea level pressure values (SLP) obtained
for the 16 grid points distributed over the Iberian Peninsula.
This database is available for the majority of the northern
hemisphere in intervals of 5° of latitude by 5° of longitude.
The same grid was used as in the study carried out by Trigo
and DaCamara (2000). This method allows for a maximum
of 26 different CWTs. Two of them are the so-called “nondirectionals”: “Pure anticyclonic” (A) and “Pure cyclonic”
(C). The next eight weather types are known as “pure”, and
are characterised by a specific predominant wind component,
without emphasising the influence of a high or low, and
they are N, S, E, W, NW, SW, SE and NE.
The remaining sixteen weather types are the so-called
Calvo et al., Aerosol and Air Quality Research, 12: 856–878, 2012
860
a)
b)
“Saharan 500 m (S)”
c)
“Saharan 1500 m (S)”
d)
“Saharan 3000 m (S) ”
e)
“Tropical Maritime (Tm)”
Fig. 3. a) Air mass classification: Arctic (A), Continental (C), Mediterranean (M), Saharan (S), Local (L), Maritime Tropical
(Tm) and Maritime Polar (Pm), b–j) Examples of 120 h backtrajectories (FNL data) at 500 m, 1500 m and 3000 m for each
air mass category.
Calvo et al., Aerosol and Air Quality Research, 12: 856–878, 2012
f)
“Polar Maritime (Pm)”
g)
“Mediterranean (M)”
h)
“Continental (C)”
i)
“Artic (A)”
j)
“Local (L)”
Fig. 3. (continued).
861
Calvo et al., Aerosol and Air Quality Research, 12: 856–878, 2012
862
(Table 2) may be explained by the increase in the production
of HNO3 from gaseous precursors during photochemical
activity, and by a displacement of the balance from the
particulate phase (NH4NO3) towards the gaseous phase
(NH3 and HNO3) (HNO3 + NH3 ⇌ NH4NO3) (Stelson and
Seinfeld, 1982; Gupta et al., 2003).
When compared to values measured in sites far from
intense anthropogenic activities, such as Banizoumbou (Niger
- 12.3 μeq/L NO3−) or Katibougou (Mali - 9.7 μeq/L NO3−)
(Galy-Lacaux et al., 2009), this nitrogeneous compound seem
high concentrated in Viznar. These latter are more consistent
with those found by Mphepya et al. (2004) for the
Amersfoort site (25.0 μeq/L NO3−) influenced by industrial
NOx emissions. However, Viznar station register similar
NO3− concentration to those observed at different Spanish
EMEP stations (e.g. Zarra (24 μeqN/L) and Risco (26
μeqN/L)) (EMEP, 2005) and at some rural and coastal
environments (Avignon –France- (24 μeqN/L) (Celle-Jeanton
et al., 2009), Izmir –Turkey- (23 μeqN/L) (Al-Momani et
al., 1995) and Sardinia –Italy- (29 μeqN/L) (Le Bolloch and
Guerzoni, 1995) (Table 3).
With regard to nitrate in link with synoptic situation and
meteorological conditions, the highest VWM values were
recorded in pure circulation of the N, NE, E and SE
between 28 and 35 μeq/L NO3− (with mainly easterly
winds). None of the hybrid cyclonic weather types exceed
24 μeq/L. In the hybrid anticyclonic weather types, the
highest values were recorded for the AN, ANE, AE and
ANW types, with values of between 40 and 94 μeq/L NO3−.
The Saharan and Local categories stands for the highest
VWM concentrations which means that both long range
transport and local sources influence the nitrate chemistry.
The high VWM mean concentrations in Saharan origin
airmasses are discussed in the acid contribution part.
The Mediterranean category includes the highest
concentrations of NO3− among the three maritime categories.
The Mediterranean zone is characterised by a complex
meteorology that favours the aging of the contaminated air
masses in the basin (Millán et al., 1997) and induces high
levels of atmospheric particles (Artiñano et al., 2001;
Querol et al., 2001; Lyamani et al., 2006). As a result, the
Mediterranean basin may represent a temporary reservoir
“hybrid” types, a result of the combination between one or
two cyclic types with the eight predominant wind types
(AN, ANW, AW, ASW, AS, ASE, AE, ANE, CN, CNW,
CW, CSW, CS, CSE, CE and CNE). Extended information
on this classification may be found in Trigo and DaCamara
(2000) and Castro et al. (2010).
RESULTS
Rainwater Chemical Composition and Wet Deposition
The entire database enables to estimate the mean chemical
composition of precipitations and the corresponding wet
deposition over the 2002–2006 period. Table 1 summarizes
the annual VWM means and associated standard deviations.
To better characterize dominant meteorological influences
and airmasses pathways, the database of rainwater
chemical composition has been also analysed through both
classifications; Fig. 4 and Fig. 5 provide these clustered
values of the VWM.
Nitrogen Contribution
In order to evaluate nitrogen deposition, the determination
of inorganic nitrogen (NO3−-N and NH4+-N) has been
considered as an effective approach and it has been widely
adopted in America and Europe (Holland et al., 2005; Yu
et al., 2011). In Viznar, the annual VWM concentrations of
nitrate and ammonium are 22.5 and 24.8 μeqN/L respectively.
After calcium and sulphate, they stand for the third most
important contribution to the rainwater chemical composition.
a) Nitrate
Nitrate is one of the nitrogenous contribution to the
chemical composition of precipitation. The HNO3 (gaseous)
which results from the oxidation of NOx is water soluble,
meaning it is washed away by precipitation, constituting
one of the most important sources of NO3− in rainwater
(Kumar, 1986). In the case of nitrate, it is important to
consider the variations in the efficiency of conversion from
NO2 to gaseous HNO3; in summer, this conversion occurs
rapidly, while in the winter it is slower (Van Egmond and
Kesseboom, 1985; Ruijgrok et al., 1992). Also, a higher
concentration of NO3− in the summerly precipitations
Table 1. Volumetric mean (VWM) and standard deviation (VWSD) recorded during each of the years of the study and during the
whole period (2002–2006). All of the concentrations included are in μeq/L with the exception of the pH and conductivity (μS/cm).
2002
pH
SO42−-S
NO3−-N
NH4+-N
Na+
Mg2+
Ca2+
Cl−
H+
K+
Cond.
2003
2004
2005
2006
2002–06
VWM
VWSD
VWM
VWSD
VWM
VWSD
VWM
VWSD
VWM
VWSD
VWM
VWSD
6.3
34.9
21.4
19.7
20.3
13.2
41.3
25.5
0.66
3.52
13.1
0.3
23.0
17.3
20.8
20.9
12.0
54.0
18.6
0.45
1.98
10.5
6.3
30.7
20.5
21.6
19.1
14.3
46.1
25.8
0.57
3.07
13.2
0.3
21.2
20.3
17.9
14.3
18.4
85.6
15.5
0.31
2.22
12.9
6.3
41.5
25.6
22.7
16.5
13.8
53.0
25.3
0.53
4.38
13.8
0.2
32.3
23.4
13.1
10.6
14.8
59.7
30.5
0.26
3.30
10.9
6.6
39.1
24.7
28.7
19.5
19.9
76.8
18.5
0.30
3.86
18.4
0.2
28.1
21.2
15.8
15.2
15.5
75.0
11.7
0.12
2.32
13.5
6.7
26.4
22.1
32.1
18.1
16.1
76.5
22.3
0.28
3.21
17.0
0.4
28.2
28.8
22.1
18.4
17.1
96.4
21.6
0.35
1.80
14.8
6.4
34.4
22.5
24.8
18.7
14.8
54.8
24.4
0.51
3.58
14.6
0.3
26.5
21.8
18.9
16.4
15.5
74.4
19.9
0.36
2.41
12.4
Calvo et al., Aerosol and Air Quality Research, 12: 856–878, 2012
Precipitation record
Precipitation record (mm)
700
100
Number of cases
600
80
500
60
400
300
40
200
20
100
0
0
S 500
b)
300
Number of cases
a)
863
S 1500
2SO
SO424 _S
S3000
NO
NO33 _N
+
NH
NH4+
4 _N
PM
TM
+
Na
Na++
Na+
M
L
Mg2+
Mg2+
Ca2+
Ca2+
ClCl-
TM
M
C
H+
H+
K+
K+
VWM VWM (eq L-1)
250
200
150
100
50
0
S 500
25
Conductivity
S3000
PM
L
C
pH
7
-1
S cm
20
6.5
15
6
pH
c)
S 1500
10
5.5
5
0
5
S 500
S 1500
S3000
PM
TM
M
L
C
Fig. 4. a) Precipitation records (mm) and number of cases, b) Volumetric mean (VWM) for the components analysed (in
µeq/L) and c) pH and conductivity for the different air masses categories established.
(for anthropogenic aerosols) and an additional source
(potential seasalt contribution) of atmospheric aerosols for
the study area (McGovern et al., 1999).
b) Ammonium
The second contribution to nitrogeneous rainwater
composition is of ammonium. Its presence in precipitations
results of the condensation of aerosols containing ammonium
and of the incorporation of gaseous ammonia in cloud
droplets. Major sources of ammonia are known to be natural
or fertilized soils, excrements of human and animals, and
wood burnings. Maximum ammonia concentration were
registered during summer: 36, 30, 22, 17 μeqN/L in summer,
spring, winter and autumn, respectively), coinciding with
the minimum precipitation registered (Table 2).
NH4+ concentrations at Viznar were similar to those
registered at Albany (USA) (27 μeq/L) in an urban
environment (Khawaja and Husain, 1990) - or the coastal
place of Sardinia (Italy) (25 μeq/L) (Le Bolloch and
Guerzoni, 1995) but higher than those observed at an
ecuatorial forest in Camerún (Africa) (Sigha-Nkamdjou et
al., 2003) or at Adirondack Mountains (New York) (Ito et
al., 2002) that register 10.5 μeq/L. Rural places such as
Alcañiz in Spain (Alastuey et al., 2001) registered values
Calvo et al., Aerosol and Air Quality Research, 12: 856–878, 2012
a)
Precipitation record
Precipitation record (mm)
500
60
Number of cases
50
400
40
300
30
200
20
100
10
Na
Na
Ca
Ca2+
2+
-
AS
AE
+
Cl
Cl-
ANE
SE
AN
CSE
CE
ASW
CS
CNW
Mg2+
Mg
CS
CN
CW
+
NH4 _N
NH4+-N
CN
+
NO
NO3--N
3 _N
CSW
S
CNE
ANW
E
AW
A
SW
2-
SO4 _S
SO42--S
600
NW
N
NE
C
0
W
0
b)
Number of cases
864
+
H
H+
K
K+
VWM ( eq L-1)
500
400
300
200
100
Conductivity
60
AS
ANE
AE
SE
CSE
AN
ASW
CE
CNW
CSW
CW
CNE
S
ANW
E
AW
A
NW
NE
SW
N
C
c)
W
0
pH
7.5
50
7
6.5
30
pH
S cm-1
40
6
20
5.5
10
ANE
AS
CSE
SE
AE
ASW
AN
CS
CE
CN
CNW
CNE
CW
CSW
ANW
S
E
AW
NW
A
N
NE
SW
5
C
W
0
Fig. 5. a) Precipitation records (mm) and number of cases, b) Volumetric mean (VWM) for the components analysed (in
µeq/L) and c) pH and conductivity for the different categories of Circulation Weather Types (CWT) established.
higher than 100 μeq/L NH4+, similar to those registered at
urban environments such us Shanghai (China) (Huang et
al., 2008) or México (Báez et al., 2007) (Table 3). Lower
concentrations have been registered in Banizoumbou (Niger,
12.9 μeq/L) or Katibougou (Mali - 17.4 μeq/L) (Galy-Lacaux
et al., 2009) and similar to those recorded for for the
Amersfoort site (22.3 μeq/L) influenced by industrial NOx
emissions (Mphepya et al., 2004).
Ammonium has the highest values in pure circulation for
the N, E and SE (with easterly winds) of between 30 and 48
μeq/L NH4+. In the pure anticiclonic category presents the
second higher value with 51 μeq/L NH4+. In the hybrid
cyclonic weather types 30 μeq/L NH4+ was not exceeded,
while in the hybrid anticyclonic weather types there are
values in excess of 50 μeq/L NH4+ for AN and ANE. These
results show that the hybrid types with cyclonic circulation
are associated with lower volumetric concentrations, due
to the significant dispersion of contaminants that occurs.
High VWM concentrations of nitrogeneous compounds
are found in airmasses of Saharan, continental and local types.
The events of arrivals of European air masses have been
explored by authors such as Carratalá and Bellot (1998),
Alonso et al. (2000), Gangoiti et al. (2002) or Viana et al.
(2003). It is complicated to establish which part of the
Calvo et al., Aerosol and Air Quality Research, 12: 856–878, 2012
865
Table 2. Mean seasonal precipitation (P in mm), number of precipitation events (N) and seasonal volumetric concentrations
(VWM) in µeq/L (except for the pH and conductivity - in µS/cm) with their standard deviations (VWSD) for each of the
parameters studied.
P
N
pH
SO42−-S
NO3−-N
NH4+-N
Na+
Mg2+
Ca2+
Cl−
H+
K+
Cond.
WINTER
138
105
VWM
VWSD
6.4
0.2
30.2
16.7
18.6
13.3
22.3
16.1
22.5
16.1
12.9
8.8
34.7
34.8
30.3
27.2
0.5
0.3
3.4
1.5
12.7
7.0
SPRING
158
102
VWM
VWSD
6.3
0.4
41.2
24.6
26.6
21.4
29.9
21.8
17.2
15.0
14.0
13.0
56.3
59.8
20.5
12.4
0.6
0.4
3.9
2.0
15.6
11.8
SUMMER
27
23
VWM
VWSD
6.9
0.2
68.5
66.2
50.9
53.4
35.9
27.0
22.4
21.1
40.9
42.7
206.2
206.4
24.2
17.1
0.1
0.1
6.2
7.0
34.5
29.6
AUTUMN
167
114
VWM
VWSD
6.4
0.3
25.7
17.2
16.7
13.4
17.2
9.8
16.4
16.9
13.0
9.7
45.4
38.0
22.7
17.2
0.5
0.3
3.0
1.6
11.6
7.8
Table 3. Volumetric weighted mean (VWM) registered in different locations around the worl (µeq/L except pH).
Place
Environment
Period
pH SO42− NO3− NH4+ Na+ Mg2+ Ca2+ Cl−
K+
a
Ontario (Canada)
Urban
1984–86 5.3 64.0 11.0 17.0 3.0
3.0 13.0 5.0
1.0
Albany (USA)b
Rural
1986–88 4.2 68.0 45.0 27.0 5.0
3.0
10
8.0
6.0
Rural
1997–99 5.2 47.0 24.0 14.1 30.7 10.0 57.1 37.2 5.7
Avignon (France)c
Urban/Costal
1992
5.6 66.0 23.0 43.0 117.0 101.0 81.0 117.0 17.0
Izmir (Turkey)d
Rural
1995–96
129.1 52.4 101.2 13.5 22.4 277.0 49.4 15.3
Alcañiz (Spain)e
Costal
1996–97 5.2 90.0 29.0 25.0 252.0 77.0 70.0 322.0 17.0
Sardinia (Italy)f
Costal
1995–97 6.2 19.0 10.0 18.7 15.0 5.2 20.2 18.0 1.8
RRL (India)g
Urban
2000–01
128.0 40.8 20.4 33.1 55.5 150.7 33.9 33.9
Tirupati (India)h
Urban
2001–02 5.8 61.9 42.6 92.4 7.0
2.5 26.4 9.6
2.1
Méxicoi
Urbanized area
2003
5.2 47.3 31.3 65.7 37.0 9.3 26.9 33.4 2.0
Melle (Belgium)j
Urban
2005
4.5 199.6 49.8 80.7 50.1 29.6 204.0 58.3 14.9
Shanghai (China)k
Rural/Industrial/
Ghore El-Safi
2006–07 6.9 112.4 67.3 75.4 130.6 93.12 165.3 142.4 85.2
Costal
(Jordan)l
Adirondack
Adirondack
88–99
4.4 36.9 22.6 10.5 1.6
1.0
3.6
2.1
0.3
Mountains
(New York)m
n
Urban
2002
5.7 15.9 2.7 30.5 10.9 4.6
9.8
9.2
3.2
Guaiba (Brasil)
Ecuatorial forest 1996–00
5.1
6.9 10.5 4.0
2.4
8.9
4.3
5.0
Camerún (Africa)o
EMEP
2003
5.2 44.3 42.1 65.7 5.7
8.3 48.4 6.5
2.0
Illmitz (Austria)p
EMEP
2003
4.8 31.8 42.8 52.8 9.1
5.0 26.9 10.4 3.1
Ispra (Italy)p
Kollumerwaard
EMEP
2003
5.4 25.6 29.3 47.8 110.0 24.6 18.0 141.3 5.1
(Netherlands)p
p
EMEP
2003
5.0 54.3 48.5 40.0 297.0 57.5 50.4 278.9 9.5
Niembro (Spain)
EMEP
2003
6.4 25.0 23.6 9.3 13.5 5.8 35.9 22.6 4.6
Zarra (Spain)p
EMEP
2003
5.7 34.9 25.7 36.4 24.8 8.8 34.9 30.2 3.8
Risco Llano (Spain)p
EMEP
2002–06 6.4 34.4 22.5 24.8 18.7 14.8 54.8 24.4 3.6
Víznar (Spain)q
a
Zeng and Hopke (1989); b Khawaja and Husain (1990); c Celle-Jeanton et al. (2009); d Al-Momani et al. (1995);
e
Alastuey et al. (2001); f Le Bolloch and Guerzoni (1995); g Das et al. (2005); h Mouli et al. (2005); I Báez et al. (2007);
j
Staelens et al. (2005); k Huang et al. (2008); l Al-Khashman (2009); m Ito et al. (2002); n Migliavacca et al. (2005);
o
Sigha-Nkamdjou et al. (2003); p EMEP (2005); q Present study.
pollution is attributable to long-distance transportation from
Europe and/or from local or regional emissions (Viana et
al., 2003; Escudero et al., 2007).
The nitrate and ammonium ions increase their
concentrations with low vorticities from the W and S (i.e.
they are negatively correlated with ZW and ZS) (Table 4).
Fig. 6(a) shows monthly VWM of inorganic nitrogen
(NH4+ and NO3−) and NH4+/NO3− during the five years of
study. It can be observed important variations of VWM
with time, with an opposite trend to precipitation (Fig.
6(b)), indicating a dilution effect of rainwater on inorganic
nitrogen concentration. This fact pointed out that quantity
866
Calvo et al., Aerosol and Air Quality Research, 12: 856–878, 2012
Calvo et al., Aerosol and Air Quality Research, 12: 856–878, 2012
a)
867
NH4_N
NH4+
300
3
NO3_N
NO3NH4+/NO3NH4/NO3
200
2
150
100
1
NH4+/NO3-
VWM (eqN L -1)
250
50
Apr
Jul
Jan 06
Apr
Oct
Jan 06
Oct
Oct
Jul
Apr
Jan 05
Oct
Jul
Apr
Jan 04
Oct
Jul
Apr
Jan 03
Oct
Jul
Apr
0
Jan 02
0
200
Precipitation (mm)
b)
150
100
50
Oct
Jul
Jul
Apr
Apr
Apr
Jan 05
Jan 04
Jan 04
Oct
Oct
Oct
Jul
Jul
Jul
Jan 03
Oct
Jul
NH3+NH4+
NH3+NH4+
NO3NO3-
3
g N m-3
Apr
4
Apr
c)
Apr
Jan 02
0
2
1
Oct
Jul
Apr
Jan 06
Oct
Jul
Apr
Jan 05
Oct
Jul
Jan 03
Oct
Jul
Apr
Jan 02
0
Fig. 6. a) Monthly volume weight mean of inorganic N (NO3−-N and NH4+-N) and ratio (NH4+-N)/(NO3−-N) during the
studied period, b) monthly variation of precipitation and c) monthly evolution of NH3 + NH4+ and NO3− in the aerosol
composition during the studied period.
of water precipitated plays an important role in the
concentrations of the the different ions studied. It can’t be
forgotten that previous studies have observed that most of
the scavenging occurs in the first 2 mm of rain registered
— between 40% and 80% of the wet-only deposition of
the major ions (Alastuey et al., 2001).
It can be observed an important variation of VWM with
time, with an opposite trend between precipitation heights
and nitrogenous aerosol concentration (Fig. 6) (EMEP,
2012). This means that wash out is efficient to clean up the
air of aerosols. But this contribution of nitrogenous aerosol
compounds through wash out in total nitrogenous
concentrations in precipitations does not seem to affect the
variability of the VWM. Thus there are no seasonal
Calvo et al., Aerosol and Air Quality Research, 12: 856–878, 2012
868
constraints from the nitrogenous aerosol component on the
full signal of nitrogenous concentrations in precipitations.
Thus this nitrogenous aerosol component may be diluted in
the whole signal of direct precipitation of nitrogenous
compounds.
If we focuss on the ratio NH4+/NO3−, we can see that it
has increased during the last year of study due mainly to a
decrease in NO3− deposition and the increase in NH4+.
Yearly mean NH4+/NO3− ratio varied from 0.89 to 1.45,
with an average value of 1.1 in the observation period. If
we focus on seasonal ratios, values of 1.1, 0.7, 1.0 and 1.2
were registered for spring, summer, autumn and winter.
These values show a similar contribution of NH4+ and NO3−
for inorganic-N deposition, i.e., agricultural and industrial
activities.
The slightly higher ratios in winter and spring could be
related to the NH3 volatilization induced by application of
N fertilizer and/or for the soil freeze/thaw cycle that could
promote NH3 volatilization (Edwards and Killham, 1986;
Yu et al., 2011)
Acidic Contribution
No acid rain problems were detected in Víznar (the pH
was always higher than 5.6), as the pH of the rainwater
collected varied between 5.7 and 7.5 (the average value for
the whole of the study interval was 6.5 ± 0.4). Acidity in
rainwater may be neutralized by mineral dust , high loaded
in carbonates, or by ammonium. Potential acidity of
precipitation is often linked to the presence of organic
acids or mineral ones, such as sulphuric and nitric acids.
The organic part of acidity cannot be discussed here as
formate or acetate were not analysed here.
A labelled “acidity factor” has been found when PCA
was applied (Table 5), This factor explains 11.5% of the
total variance of the investigated data set and include high
loadings negatively correlated for pH and H+, as expected.
The neutralization of rainwater is sustained by a good
correlation (Table 4) observed between the SO42−-S and
NO3−-N with the Ca2+, Mg2+ and K+ with r > 0.79, as well as
with the Na4+-N with r > 0.53. These important correlations
may be due to the atmospheric chemical reactions between
these elements (absorption of acidic elements such as
sulphuric acid and nitric acid on the aerosols, and their
subsequent reaction with rich alkaline components in the
carbonates present in the particulate material) (Tu et al.,
2005; Zhang et al., 2007). As it can be observed in Fig. 7,
the calcium, sodium, ammonium and magnesium ions
seem to be dominant in the neutralisation of the rainwater
(Ca2+ has the highest NF (1.1 ± 0.8), followed by NH4+-N
(0.4 ± 0.3), Na+ (0.4 ± 0.3) and Mg2+ (0.3 ± 0.2). The
potassium has the lowest NF, with a value of 0.07 ± 0.04).
No significant correlation were registered between the H+
and SO42−-S and NO3−-N (r = –0.20 and –0.26, respectively)
due to the important role that Ca2+ plays in the neutralisation
process (Topçu et al., 2002), as can be seen when we
observed that Ca2+ has the highest NF. Also, in the
atmosphere ammonium- mainly associated with farming
and biomass burning- mainly combines with sulphate and
nitrate to form ammonium sulphate and ammonium nitrate,
respectively (Meng and Seinfeld, 1994; Redington and
Derwent, 2002; Pathak et al., 2009).
High pH levels, as well as high concentrations of cations
(mainly Ca2+) and marine ions characterise the chemical
composition of the rainwater associated with incursions of
Saharan dust (Saharan (n = 62) and Saharan 1500 m (n =
44) (Savoie et al., 1992; Prospero et al., 1995; Ávila and
Alarcón, 1999; Kandler et al., 2007). The events included
in Saharan 3000 m (n = 23) category have a typically
Table 5. Principal component analysis of the different parameters analysed in the precipitation collected at the EMEP
station in Viznar during the period 2002–2006, as well as the different parameters used to calculate the weather types.
Conduc
SO42−-S
Ca2+
Mg2+
NO3−-N
K+
NH4+-N
Z
ZW
ZS
H+
pH
F
WF
SF
Cl−
Na+
% Total variance
Factor
1
.950
.936
.933
.930
.916
.865
.500
–.102
–.087
–.083
–.130
.249
–.249
–.245
–.003
.101
.479
38.8
Load
2
–.096
–.077
–.016
–.032
–.089
–.030
–.283
.981
.899
.700
–.005
–.022
–.004
–.297
.290
.189
–.057
14.7
Vorticity
Factors
3
.176
–.015
.218
.215
.059
.004
.129
–.022
–.090
.087
–.964
.952
–.010
–.015
.107
.017
.069
11.5
Acidity
4
–.116
–.130
–.079
–.072
–.211
–.092
–.301
–.019
–.117
.133
–.042
–.004
.756
.730
.665
–.008
.109
9.4
Flow of winds
5
.130
.156
.057
.066
.022
.170
–.002
.036
–.069
.176
–.030
.025
.072
.272
–.338
.838
.719
6.3
Marine
Calvo et al., Aerosol and Air Quality Research, 12: 856–878, 2012
869
Fig. 7. Relationship between the sum of the concentrations of Ca2+, Mg2+, NH4+-N and Na+ and the sum of SO42−-S and
NO3−-N.
Continental and Mediterranean origin at low levels (500 m
and 1500 m). If we compare the precipitation events
included in the Saharan 3000 m type with those classified
as Continental or Mediterranean, the Saharan 3000 m
category has higher volumetric means for almost all the
elements (except for K+, H+, Ca2+ and the pH). However,
applying the non-parametric Mann-Whitney test reveals
that there are no significant differences for any of the ions
studied in the precipitation between the Saharan 3000 m
category and the Continental and Mediterranean categories,
which indicates that the Saharan 3000 m air mass does not
seem to have a marked influence on the chemical composition
of the precipitation.
When analysing the characteristics of the days included in
each category, it is necessary to take into account that some
specific situations may arise that cause their characteristics
to vary from those expected due to their origin. For example,
some days characterised as Saharan do not have the typical
chemical characteristics described for ‘red’ African rains
with high alkalinity and a high concentration of cations
(Loye-Pilot et al., 1986, 1990; Rodà et al., 1993; Avila et
al., 1997). As Avila and Alarcón (1999) discuss, this may
be due to the fact that the rains from Africa may only have
these identifying characteristics if they cross through a
cloud of dust on their way over the African continent at the
correct height. The elevation of dust is more frequent under
certain humidity and temperature conditions that occur
especially in the spring and autumn (Morales, 1979). Also,
some days included in the Polar Maritime category have
typical characteristics of Saharan events (basic pH and a
high concentration of cations and sulphate). In this case, we
interpret that this air mass, despite being defined as maritime
as a result of coming from the Atlantic, could be influenced
by clouds of African dust moving towards the west over the
Atlantic, meaning it would become enriched by African
materials. The transport of African dust over the north
Atlantic is extensively described in the literature (Prospero
and Nees, 1986; Duce et al., 1991; Prospero, 1996).
Sulphate has the highest VWM values in pure circulation
of the N, NE and NW between 35 and 54 μeqS/L (with
northerly winds). In the hybrid cyclonic weather categories,
the highest values of nearly 39 μeqS/L are with CNE and CS
types. In the hybrid anticyclonic weather categories, there
are values of around 63 μeqS/L for AN, ANE and ANW. A
good correlation was seen between the nitrate and sulphate
(r = 0.83) (Table 4), which is attributable to the similar
chemical behaviour they have in the precipitation, as well as
to the co-emission of their precursors, SO2 and NOx (mainly
due to the burning of fossil fuels, and also to the burning of
biomass) (Zhang et al., 2007; Huang et al., 2008). These
two elements have an important anthropogenic contribution,
as can be seen when we observed EnFcrustal (Table 6) with
values of 31 and 200 for sulphate and nitrate, respectively.
Marine and Terrigeneous Contributions
The annual VWM concentrations of sodium an chlorine
are respectively of 18.7 μeq/L and 24.4 μeq/L (Table 1).
The Cl− is very well correlated with the Na+ (r = 0.75)
(Table 4), suggesting a marine origin for both ions. This fact
is confirmed when the principal component analysis is
carried out, where both elements are grouped in a factor
explaining 6.3% of the variance (Table 5). When enrichment
factors are analysed, it can be seen that the Cl− has a
clearly marine origin (EnFcrustal = 123.37 and EnFseawater =
1.12, by using Na+ as reference element) (Table 6).
The Cl− and the Na+ present a similar behaviour, with
significant joint concentrations in pure circulations of the
SW and NW. It was seen that chlorine and sodium jointly
present the highest volumetric concentrations in the hybrid
weather types CW and AW, with mean VWM values in
excess of 30 μeq/L. That is, if the wind component is from
the west both with an anticyclone and a cyclone, then there
are high chlorine and sodium values. The cyclonic circulation
(C) which occurs when there is a stagnant low from the
NW zonal flow, and which is usually reinforced by a low
at high altitude (500 hPa), favours high concentrations of
chlorine and sodium. This fact is corroborated when the
Pearson correlation coefficient is observed. Thus, chlorine
and sodium are positively correlated with the WF (i.e. high
WF values favour the arrival of marine ions) (Table 4).
Calcium is the most abundant species in the Viznar
rainwater (annual VWM of 54.8 ± 74.4 μeq/L). The cations
Ca2+, Mg2+ and K+ are well correlated, with values of rMg-Ca
= 0.94, rK-Ca = 0.55 and rK-Mg = 0.64, suggesting a crustal
origin. However, Mg2+ and K+ EnFs (Table 6) seawater
with values lower than 10, reveal the existence of a certain
influence from the marine source in the concentration of
these two elements.
Calvo et al., Aerosol and Air Quality Research, 12: 856–878, 2012
870
Table 6. Enrichment factors of the different ions analysed in the rainwater with respect to the crustal material and seawater.
(Cx/CCa)crustal
(Cx/CCa)sample
EnFcrustal
(Cx/CNa)seawater
(Cx/CNa)sample
EnFseawater
K+
0.50
0.06
0.12
0.022
0.19
8.6
Mg2+
0.56
0.27
0.48
0.23
0.92
4.1
The calcium has the highest volumetric concentrations
in pure circulations of the N, NE and S, of between 70 and
84 μeq/L. On analysing the hybrid cyclonic categories, we
find that the highest values are reached in hybrid weather
types: 102 μeq/L for CSE and 77 μeq/L for CSW. However,
in the same way as the magnesium, the situation changes in
the presence of hybrid anticyclonic weather types (AN, ANE,
AE, ANW and AS), as here we find higher concentrations
(between 76 and 183 μeq/L).
The magnesium has the highest values in pure
circulation from the N and E between 20 and 17 μeq/L,
respectively. In the hybrid weather types, the values are
between 7 (for CW) and 19 μeq/L (for CSE). However, the
situation changes when there are hybrid anticyclonic types,
as the concentrations are between 21 and 58 μeq/L for AN,
ANE, AE and ANW. Here we can clearly observe that the
anticyclone inhibits dispersion.
In the case of the calcium and the magnesium, the South
component appears in CSE, CSW and AS, which does not
appear for any other ion. The Mann-Whitney test shows that
there are no significant differences between these weather
types and the Saharan air masses (500, 1500 and 3000 m)
for any of the ions that were studied (only for H+ when
associating the CSW with the Saharan 3000 m category).
These crustal components (Ca2+, Mg2+ and K+), together
with the antropogenic ones (SO42−, NO3−, NH4+) and
conductivity, appear positively correlated in component one
of the PCA, explaining 38.8% of the total variance (Table
5). A “pollution factor” label could be assigned to this factor
as this ion grouping may be interpreted as the dominant
precipitation chemistry type in this region (Avila and
Alarcón, 1999; Calvo et al., 2010). Furthermore, as result
of this PCA analyses, a second factor, explaining 14.7% of
the variance, contains the parameters associated with the
vorticity (Z, ZW and ZS) and another factor groups together
the three parameters associated with the flow of winds (F,
WF and SF), explaining 9.4% of the total variance.
The total shear vorticity (Z) is related with the wind
vorticity. High values are characteristic of cyclones and
anticyclones, and the lowest for pure circulations of the N,
S, W, SW, E, etc. The influence in Z comes both from
southerly shear vorticity, ZS, (r = 0.739) and westerly shear
vorticity, ZW, (r = 0.902). The total shear vorticity Z is
negatively correlated with all of the ions except Ca2+, Cl−
and H+.
Wet Deposition
The wet deposition has been calculated (mg/m2/year) for
each of the years included in the study by multiplying the
Cl−
0.0031
0.38
120
1.16
1.30
1.1
SO42−-S
0.019
0.58
31
0.13
1.96
15
NO3−-N
0.0021
0.42
200
-
VWM concentrations by the annual rainfall amount. The
concentrations for days with missing precipitation data have
consequently been assumed to be equal to the weighted
average of the period (EMEP, 2005). On representing the
wet deposition recorded for each element analysed during
the five years of the study (Fig. 8) we see that the highest
deposited amounts correspond to Ca2+, Cl− and SO42−. Mg2+
and K+ have the lowest values, with annual means of between
67 and 105 mg/m2/year and between 42 and 90 mg/m2/year,
respectively. A similar trend is seen for the majority of the
ions: a progressive decrease in the wet deposition from 2002
to 2005, then increasing in 2006, reaching the maximum
values in the five years of the study for ammonium and
calcium (with nearly 193 and 670 mg/m2/year, respectively).
If we calculate the mean annual wet deposition as the
arithmetic mean of the wet deposition of the five years of
the study, we obtain values of 270 mgS/m2/year (from the
SO42−-S), 155 mgN/m2/year (from the NO3−-N), 165
mgN/m2/year (from the NH4+-N), 212 mgNa+/m2/year, 89
mgMg2+/m2/year, 542 mgCa2+/m2/year, 422 mgCl−/m2/year,
0,25 mgH+/m2/year, and 69 mgK+/m2/year.
Focusing on nitrogen deposition, from 2002 to 2006,
yearly N deposition ranged from 111 to 193 mgN/m2/year
for NH4+-N (with the average of 165 mgN/m2/year), from
95 to 197 mgN/m2/year for NO3−-N (with the average of
155 mgN/m2/year) and from 206 mgN/m2/year to 378
mgN/m2/year for total inorganic N (with the average of
320 mgN/m2/year).
In a Romanian site in the forested clean area of Retezeat
Mountains gives a deposition of 260 and 330 mgN/m2/year
for 2000–2002 for N-NO3− and N-NH4+ respectively
(Bytnerowicz et al., 2005), similar level at Pop Ivan in the
Carpathian Mountains in Ukraine with about 190 and 380
mgN/m2/year in 2008 (Oulehle, 2010).
Inorganic-N deposition in Northern Hemisphere, ranging
from 40 to 100 mgN/m2/year were estimated by Holland et
al. (1999) during the pre-industrial period. In areas very far
away from the industrial areas, such as the QinghaiTibetan Plateau, atmospheric N deposition as low as 240
mgN/m2/year were registered (Jia et al., 2009). However,
nowadays, in central Europe, values of wet deposition of
total nitrogen above 2000 mgN/m2/year have been registered,
and in China, values as high as 6225 mgN/m2/year have
been measured (Lu and Tian, 2007; Yu et al., 2011).
Focusing on measurement networks, during 2003 to 2005,
inorganic-N deposition in rainwater quantified by the EMEP
varied from 104 to 1840 mgN/m2/year and ranged between
4 and 853 mgN/m2/year in the National Atmospheric
Deposition Program/National Trends Network (NADP/
Wet Deposition (mg m -2year-1)
Calvo et al., Aerosol and Air Quality Research, 12: 856–878, 2012
871
800
600
2002
2003
2005
2006
2004
400
200
0
SO42-
NO3-
NH4+
Na+
Mg2+
Ca2+
Cl -
K+
Ions
Fig. 8. Wet deposition (mg/m2/year for all the elements –mgN/m2/year for NH4+ and NO3− and mg/Sm2/year for SO42−)
recorded for each of the elements analysed in the rainwater during the five years of the study.
NTN) (a 200-station, rural, wet-only deposition monitoring
network throughout the continental United States, Alaska,
and Puerto Rico) (Yu et al., 2011). The values registered in
Viznar are in the low ranges in the EMEP register.
Interannual and Intra-Annual Variability
A total of 344 rain days were recorded between 1 January
2002 and 31 December 2006, with 82 events in 2002, 88 in
2003, 68 in 2004, 46 in 2005 and 60 in 2006. With regard
to the amount of rain precipitated, we have mean annual
values of 660, 578, 519, 276 and 429 mm, for the years
2002, 2003, 2004, 2005 and 2006, respectively.
If we consider the annual mean volumetric concentrations
(Table 1), we see that the highest concentrations (VWM) of
SO42−, NO3− and K+ were recorded in 2004, with values of
42 μeqS/L, 26 μeq/L and 4 μeq/L. The lowest precipitated
volume was recorded in 2005 (276 mm) and the highest
concentrations of Mg2+ and Ca2+, as well as the highest
conductivity, with values of 20 μeq/L, 77 μeq/L and 18 μS/cm,
respectively. In 2006 the highest average concentration of
NH4+ was recorded, a high concentration of Ca2+ and the
highest pH, while in 2002 the highest concentration of H+
and Na+ was recorded.
If we focus on the volumetric concentration of ammonium,
we see a gradual increase over the years, from 19.69 μeqN/L
in 2002 to 32.07 μeqN/L in 2007. This increase was also
observed in the particulate phase, where the concentation
of (NH3 + NH4+) increase from 0.4 ± 0.4 μg/m3 in 2002 to
2.0 ± 1.1 μg/m3 (Calvo, 2009). Due to the important
contribution of local category to NH4+ deposition, this
increase could be related to a change in the soil uses, in the
fertilizers used, an increasing fertilization, an increase in
the farm activity in the surroundings, etc. Indeed, ammonia
emissions at the scale of the Andalucia region increase of
about one third between 2002 and 2006 (www.prtr-es.es)
(from 5895 to 7458 ton/year). This increase seems to be
linked with the intensification of the pig farming and
associated emissions (1966 ton/year in 2002 to 3170 ton/year
in 2006). Furthermore, an increase in the number of Sahara
500 m events, associated with important concentrations of
NH4+ have been registered during the studied period (28,
31, 35, 48 and 62 events for 2002, 2003, 2004, 2005 and
2006, respectively). This fact could be a possible factor
involved in the NH4+ increased registered.
On the other hand, it needs to be taken into account that
the qualities of the nitrogen precipitation measurements are
in general quite good, as for sulfur the analytical uncertainty
is relatively low and the deposition uncertainty is about
10% (Uggerud and Hjellbrekke, 2009).
Focusing on the whole studied period, we can affirm that
the chemistry of the rainwater is dominated by Ca2+ and
SO42− (Table 1), with VWM during the studied period
(2002–2006) of 55 μeq/L and 34 μeqS/L, that constitute
28% and 17% of the total, respectively. High percentages
(of between 11 and 13%) were found of NH4+-N, Cl− and
NO3−. Na+ and Mg2+ constitute between 9% and 8% of the
total volumetric concentration that was recorded, and K+ and
H+ appear as minority elements, with percentages of less
than 2% (Table 1).
The maximum concentrations of nitrate were recorded
in the summer, as has been previously discussed. Nitrate, as
sulphate, showed, applying Mann-Whitney test, significant
differences (at significance level of 0.05), between all of
the seasons, except between the winter and autumn.
The majority of the maximum average seasonal
concentrations of the precipitation events recorded during
the study period 2002–2006 were obtained in the summer,
except for Cl− and Na+ whose maximum is in winter, and
H+ in the spring. The maximums of chlorine and sodium in
the winter may be due to the larger number of arrivals of
masses of maritime air recorded during this season. MannWhitney test showed significant seasonal differences (at
significance level of 0.05), between the winter and autumn
and summer and autumn for sodium, and between the winter
and spring and spring and autumn for chlorine. They are the
ions with the least significant seasonal differences. MannWhitney test was applied after observing significant
differences for all of the parameters that were studied by
applying the Kruskal-Wallis test.
The high volumetric concentration recorded in the summer
for calcium is especially striking, with values of 206 μeq/L
compared to 35, 56 and 45 μeq/L in the winter, spring and
872
Calvo et al., Aerosol and Air Quality Research, 12: 856–878, 2012
autumn respectively. These high calcium levels are associated
with the frequent intrusions of Saharan dust that occur during
the summer. Focusing on the seasonal percentages that
constitute the average volumetric concentrations recorded
for each of the ions studied, we can see that calcium, in the
summer, constitutes nearly 45% of the total of the
concentration recorded, compared to the 20%, 27% and 28%
it constitutes in the winter, spring and autumn respectively.
Applying Mann-Whitney test, it can be seen that calcium
only has non-significant differences (at significance level
of 0.05) between the spring and autumn. The high levels of
PM10 registered during the summer months, with mean
concentrations of 32 ± 20 μg/m3 for summer versus 17 ±
16, 24 ± 17 and 14 ± 11 μg/m3 for winter, spring and
autumn, respectively, during the studied period corroborate
these results (Calvo, 2009; EMEP, 2012). Daily mean
concentrations of around 200 μg/m3 were reached during
some summer days as a consequence of Saharan intrussions
(Calvo, 2009).
It is important to take into account the fact that during the
summers, a large number of the precipitation events that
took place left behind a small precipitated volume. As a
result, we would expect a minimum dilution, and as a result,
high volumetric concentrations of the different ions studied.
It is therefore logical that the majority of the minimum
concentrations of the different parameters being studied
were recorded in the autumn, which was the season with
the highest mean seasonal volume (Table 2) (Hansen et al.,
1994; Naik et al., 1994; Alastuey, 2001; Zhang et al., 2007).
CONCLUSIONS
This study shows the analysis of 344 days (2002–2006)
of rainwater inorganic chemical composition in a remote
regional background EMEP station in Spain. Due to its
important impacts, nitrogen contribution has been
emphasized. Nitrate and ammonium species (with annual
VWM concentrations of 22.5 and 24.8 μeqN/L, respectively)
stand for the third most important contribution to the
rainwater chemical composition. A similar contribution of
both species for inorganic-N deposition (with a yearly mean
NH4+/NO3− ratio of 1.1) has been identified. Regarding
airmasses, high VWM concentrations of nitrogeneous
compounds are found in Saharan, Continental and Local
categories. In link with synoptic situation and meteorological
conditions, the highest VWM values were registered in the
hybrid anticyclonic weather types: AN, ANE, AE and ANW
for nitrate (with values of between 40 and 94 μeqN/L) and
AN and ANE for ammonium (with values in excess of 50
μeqN/L). A gradual increase of VWM of NH4+ over the
years of study has been detected and seems to be mainly
linked with the intensification of the pig farming and
associated emissions in the Andalucia region and with the
increase in the number of Sahara 500 m events.
At the EMEP station in Víznar, no acid rain problems
were detected, and the calcium, sodium, ammonium and
magnesium ions seem to be dominant in the neutralisation
of the rainwater. Nitrate and sulphate (r = 0.83), from
antropogenic sources, seem to have a similar chemical
behaviour in precipitation, as well as to the co-emission of
their precursors SO2 and NOx. The highest VWM for sulphate
was registered in the hybrid anticyclonic weather categories,
with values of around 63 μeqS/L for AN, ANE and ANW.
Chlorine and sodium, with a marine origin, register the
highest volumetric concentrations if the wind component is
from the west both with an anticyclone and a cyclone. The
three classes of marine origin have the lowest concentrations
of the nine categories that were analysed, with the
Mediterranean class being the most contaminated. The
larger number of arrivals of masses of maritime air recorded
during winter explains the maximums VWM of chlorine
and sodium during this season.
Ca2+ and Mg2+ with a main crustal origin, present higher
concentrations in the presence of hybrid anticyclonic weather
types (between 76 and 183 μeq/L for Calcium and between
21 and 58 μeq/L for magnesium). High cation concentrations
(mainly Ca2+, with mean volumetric concentrations of up
to 150 μeq/L) characterises the chemical composition of
the rainwater associated with incursions of Saharan dust (at
the 3 levels) as well as high pH levels. The Saharan 3000
m category does not appear to have a significant influence
(according to the Mann-Whitney test) on the chemical
composition of the precipitation.
Regarding wet deposition, a similar trend is seen for the
majority of the ions: a progressive decrease in the wet
deposition from 2002 to 2005, then increasing in 2006. The
mean annual wet deposition for the different elements studied
was: 270 mgS/m2/year (from the SO42−), 155 mgN/m2/year
(from the NO3−), 165 mgN/m2/year (from the NH4+), 212
mgNa+/m2/year, 89 mgMg2+/m2/year, 542 mgCa2+/m2/year,
422 mgCl−/m2/year, 0,25 mgH+/m2/year, and 69 mgK+/m2/year.
The chemistry of the rainwater is dominated by Ca2+ and
SO42−, with VWM of 55 μeq/L and 34 μeqS/L during the
studied period (2002–2006). During summer, the majority
of the maximum average seasonal concentrations was
recorded (except for Cl− and Na+) due to the minimum
dilution experimented; a large number of the precipitation
events lefting behind a small precipitated volume. It is
important to emphasize the high VWM recorder for calcium
during summer (206 μeq/L) due to the frequent intrusions
of Sahara dust.
This study points out the relevance of long range
transport on atmospheric pollution and contributes to the
knowledge on rainwater quality in background stations in
Europe. Considering both meteorological and airmasses
studies seems to be a very useful tool for characterizing and
understanding precipitation chemical composition. Further
studies are needed in order to complete this data with aspects
such as organic deposition (mainly N-deposition) or dry
deposition in order to create a complete database that permits
to evaluate modelling exercises and improve knowledges
about future environmental and human health impacts.
ACKNOWLEDGEMENTS
The authors would like to thank Alberto Gonzalez Ortíz
(Ministry of the Environment, Spain) and Andrés Alastuey
(Jaume Almera Institut, CSIC, Spain) for the information
Calvo et al., Aerosol and Air Quality Research, 12: 856–878, 2012
provided about the EMEP station at Víznar. Ana I. Calvo
and Ana M. Vicente acknowledge the posdoc and PhD
grants SFRH/BPD/64810/2009 and SFRH/BD/48535/2008,
respectively, from the Portuguese Science Foundation
(FCT). We would also like to thank Borja Ruíz Reverter
for the classification of the back-trajectories. The authors
are also in debt to Antonio M. Ortín for the graphic design.
The authors gratefully acknowledge the NOAA Air
Resources Laboratory (ARL) for the provision of the
HYSPLIT transport and dispersion model and/or READY
website (http://ready.arl.noaa.gov) used in this publication.
This study has been supported by the Spanish Ministry
of Education (Projects CGL2007-66477-C02-01, TEC200763216), the Spanish Ministry of Science and Technology
(Projects CGL2010-18782 and CSD2007–00067), the
Andalusian Regional Government (Projects P06-RNM01503, P08-RNM-3568, and P10-RNM-6299), the European
Union through ACTRIS project (EU INFRA-2010-1.1.16–
262254) and by the Castile and Leon Regional Government
(Project LE039A10-2).
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Received for review, March 19, 2012
Accepted, June 8, 2012