The Science of the Total Enuironment,
61 (1987) 15- 22
Elsevier
Science
Publishers
B.V.. Amsterdam
~ Printed
CONTRIBUTION
PRECIPITATION
OF ALKALINE
IN ISRAEL
AND
15
in The
ACIDIC
Netherlands
SOURCES
TO
Y. MAMANE
Enuironmental
Engineering
Technion,
Haifa
32000
(Israel)
U. DAYAN
Israel
J.M.
Atomic
Energy
Commission,
Soreq
Laboratory,
Silver
Nuclear
Research
Center,
Yavne
(Israel)
MILLER
NOAA,
(Received
Air
Resources
July
2nd,
1986;
accepted
July
Spring,
24th,
MD
(U.S.A)
1986)
ABSTRACT
Event
precipitation
samples
were collected
at eight sites in Israel
during
three hydrological
years between
1979 and 1982 using bulk collectors.
The chemical
composition
of these events was
correlated
with backward
air trajectories,
to determine
sources
of acidic
and alkaline
materials
transported
to the Eastern
Mediterranean.
The four major
source regions
studied
were: Western
Europe,
Eastern
Europe,
Western
Asia and the North
African
Coast. Most of the rain falls during
the winter
season, which
is characterized
by trajectories
moving
along the Mediterranean
sea or
along the North
African
Coast. These trajectories
were associated
with alkaline
rain rich in soil
and sea components.
On the other hand air flow originating
in Eastern
Europe was associated
with
acid rain in Israel,
probably
due to the absence
of alkaline
material
in the air, mostly
carbonates,
which
could neutralize
the rain acidity.
INTRODUCTION
The chemistry of precipitation
has been the subject of detailed studies by
various research groups all over the world. Only few, however, have related
chemistry to meteorology.
Meteorological
factors may determine the composition of precipitation,
since they affect the transport of the air masses, the
evolution of clouds, and the scavenging of pollutants in and below the cloud
base. On the other hand, because of these complications,
correlation
is not
simple to determine. The “Meteorology
of Acid Deposition”
was recently the
main topic of an APCA Conference (Samson, 1984), and of other conferences
devoted to acid rain. Saxena et al. (1984) have integrated the chemistry of (acid)
rain in a two-dimensional
traject,ory model which comprises emissions, transport, dispersion and deposition of pollutants.
Analysis of precipitation
chemistry using air parcel trajectories
has also
been performed by Kurtz and Scheider (1981), Henderson and Weingartner
(1982),
Munn
et al. (1984), and Castillo
et al. (1985). Almost all groups have
0048.9697/87/$03.50
1”~ 1987 Elsevier
Science
Publishers
B.V.
16
found some dependence of rain composition (mainly acidity, sulfate and nitrate
ions) on air movement. In general, trajectory analysis provides only a general
relationship
in the synoptic scale between sources and receptor sites. It is not
always a precise tool (Castillo et al., 1985), and in some cases trajectories are
too complex and difficult to interpret (Munn et al., 1984).
Others have related the concentration
of rain constituents to meteorological
variables. Kahl et al. (1984) found that annual variations
in meteorological
conditions have a strong effect on the relative contribution
of upwind source
regions to sensitive receptor areas in the United States. Stensland and
Semonin (1982) went even further to hypothesize that the chemistry of the
1955556 precipitation
was not different in acidity from the current levels of
eastern North America, if the 1955-56 data is adjusted for current concentrations of alkaline constituents.
They suggested that the drought in the mid1950s which affected large parts of the Midwest and Southeast United States,
caused dust storm events which neutralized the acidity of precipitation.
Doty
and Semonin (1984) used trajectory analyses to provide evidence for potential
transport of dust storm aerosol and its incorporation
with precipitation
in the
Midwest; however, that study was limited to one event only.
In Israel, precipitation
samples have been collected since 1979 and analyzed
for pH, conductivity
and major anions and cations (Mamane, 1984). Preliminary analyses of data from three hydrological years (19791982) indicate that pH
values range from fairly acidic rain events (pH 3 4.1) to very alkaline
(pH 6 8.7). In this paper the interrelationship
between precipitation
chemistry
and meteorological
parameters in the form of back trajectories at the 850mb
pressure level is described.
PRECIPITATION
CHEMISTRY
NETWORK
The sampling and analytical methods have been described elsewhere (Mamane, 1984) and only a short summary is included here. Bulk precipitation
samples were collected manually on an event basis following WMO’s protocols
(WMO, 1978). Rain events usually last from one to five days during the winter
months of November to March. All rain samples were shipped from the various
stations to the Technion Environmental
Engineering
Laboratories
for analysis, which included precipitation
amount, pH, sulfate, nitrate, chloride, and
ammonium ions, the metals sodium, potassium, calcium and magnesium, alkalinity and conductivity.
BACK
TRAJECTORY
MODEL
The modified trajectory model of the Air Resources Laboratory
(ARL) (Harris, 1982) was used to identify the origins of airflow patterns during precipitation in the Eastern Mediterranean.
The original ARL model was described by
Hefter and Taylor (1975), but the essential principles of the modified version are
presented here. The operational
model uses meteorological
parameters
to
investigate long-range transport and dispersion of effluents on a regional scale.
17
The input wind data for the ARL model consist of gridded wind components at
standard pressure levels produced by a global atmospheric model. This model
calculates trajectories
to each receptor twice daily at standard pressure surfaces: surface level, 850mb, and the 700 mb level. The interpretation
of rain
chemistry and backward trajectories
was mostly based on the 850mb level,
which is around the height of the boundary layer. As such it represents the
layer of air transport which may affect processes in and below the clouds.
Trajectories were calculated for each day for a period of 5 years, 19781982,
and were grouped according to the major source regions in the area (Dayan,
1986). Based on past studies in the region (Dayan and Graber, 1981: Martin et
al., 1984; Dayan, 1986) each trajectory
reaching Israel during a rainy period
was assigned one of four sectors: northwest, north, east, or southwest.
Figure 1 shows a map of the Mediterranean
Sea with the main trajectories
arriving in Israel from the major source regions: (1) a long fetch of maritime air
masses from Northwest
Europe crossing the Mediterranean
Sea (northwest
sector); (2) north-northwest
continental
flow originating
in Eastern Europe
(northern sector); (3) East Asia flow (eastern sector); and (4) southwest flow
along the North African coast and the Saharan desert. In the winter season
most of the trajectories are either assigned to sector 1 (45%) or sector 4 (35%).
Sector 2 comprises only 17% and sector 3 only 3%. Normally, precipitation
is
not associated with trajectories from sector 3 (Dayan, 1986).
RESULTS
AND
DISCUSSION
The precipitation-weighted
mean concentrations
for three hydrological
years, 19791982, were very distinct and different
from those reported for
northwest Europe and northeast America: (a) precipitation
in Israel is mostly
F’ig. 1. Map of the main
sectors
1 and 4.
trajectories
arriving
in Israel.
During
winter
most
trajectories
are from
18
alkaline (pH 6.5 i- 0.8, range 4.1L8.7); (b) precipitation
contains high concentrations of soil minerals and sea salts (Mamane, 1984).
We chose one station, in the coastal plain of central Israel, the Beit-Dagan
station, to correlate chemistry with meteorology. This station regularly measures meteorological
parameters, as well as vertical profiles of wind and temperature. This data was incorporated
in the modified trajectory
model to
provide back trajectories
each 12h. Each rain event was characterized
by
several trajectories,
sometimes of different origin. Out of 27 rain events at
Beit-Dagan, over a period of three hydrological
years, 12 were mostly associated with the Northwest Europe trajectory (trajectory
l), eight were from
Northeast
Europe (trajectory
2) five originated
in the southwest over the
North African Deserts (trajectory 4), and the remaining two were of undefined
category. Table 1 lists the precipitation-weighted
mean concentrations
(in
peq 1 ’ ) for each category. It shows rather clearly that there are differences
between the three major categories: air flow originating
in Northeast Europe
and Russia brings non-alkaline
precipitation,
i.e. pH 5.5, while trajectories
from Northwest Europe and North Africa bring alkaline rain with pH 6.4- 6.7.
Although the number of cases is limited the difference between trajectory 2 and
other trajectories in hydrogen ion concentration
is significant above the 0.05
level. The calcium ion concentration
on the other hand is higher, as expected,
for trajectory
4 which passes over the North African deserts. It has been
documented
that dust blowing from the Saharan desert towards the East
Mediterranean
is rich in calcites (Ganor. 1975; Ganor and Mamane, 1982). The
behavior of sulfates in precipitation
is more complex; on one hand the sulfate
ion is associated with the “acidic”
rain originating
in Northeast
Europe
(trajectory 2) but also with sea spray (trajectory 1) and desert particles (trajectory 4) as reported by Mamane et al. (1980); the averages for sulfate ion for
trajectories 1, 2 and 4 are 77, 111 and 143peql ml respectively, after correction
for sea salt. It should be stressed again that assigning one trajectory to a rain
TABLE
1
Precipitation-weighted
(197%1982;
Beit-Dagan
mean
station)
concentrations
Trajectory
Number
PH
CaL 4
Mg’
K’
Na’
NH,
NO,
Cl
so:-
of rain
events
12
6.4
217
95
6.5
229
14.5
18.6
332
105
(,ueq I ‘) for
back
1
Trajectory
8
5.5
190
128
11.7
240
15.3
19.3
381
140
trajectories
2
arriving
in Israel
Trajectory
5
6.7
368
211
37.1
458
13.1
28.6
564
199
4
19
event lasting a few days was not a straightforward
task, due to changes in air
flow during the rain event.
Another way to study the relationship
between air trajectories
and precipitation
chemistry is to look at the extreme pH cases. We chose all rain
events, at all stations during the three winters, where the pH was < 5.1 and
> 7.6; 9 and 10 cases were found respectively. Table 2 lists the mean concentrations for the low and high pH cases. The acidic precipitation
events were
completely different from the alkaline events. The former contained less Ca,
Mg, K, Cl and SO, ions, but more hydrogen and nitrate ions, the ammonium and
sodium ions were about the same. We could find no explanation
for the higher
chloride ion levels in alkaline precipitation.
The ion balance in acidic precipitation is within 2% of the ions listed in Table 2. In the alkaline cases the
anion levels were only 76% of the cations. The missing anion could be bicarbonate, which was not measured directly and is known to be a constituent
of
calcareous soils.
The trajectories
associated with the nine acidic precipitation
events were
mostly (7 out of 9) from Northeast Europe (trajectory
2), one was mixed, but
again mostly from Northeast
Europe and for another no trajectories
were
available. Thus one may conclude that trajectories from Northeast Europe are
associated with acidic rain. Industrial
emissions from these regions and the
absence of buffering
constituents
results in the rain being acidic. All the
alkaline rain events, but one, were associated with trajectories 1 and 4, which
pass over the Mediterranean
and the North African deserts. In these cases the
buffering capacity of carbonate far exceeds any acidic emissions from Northwest Europe.
One alkaline rain event had seven trajectories from Northeast Europe, but
the first (as the rain event started) was from North Africa. Apparently
the
amount of alkaline material transported to the Eastern Mediterranean
during
the first 6 h was sufficient to control the subsequent chemistry of the rain.
TABLE
2
Precipitation-weighted
(197%1982)
Number
PH
Ca’ ’
Mg’
K’
Na’
NH;
NO,
Cl
SOi-
of rain
mean
events
concentrations
(peq I-‘)
for
low
and
high
Low pH
events
High pH
events
9
4.7
21.6
51.2
4.3
253
11.9
2.8
273
68
10
7.4
313
139
22.1
233
10.6
11.1
392
143
pH
rain
events
in Israel
20
Figure 2 shows an example of the trajectories for two extreme pH precipitation events, one acidic with a pH of 4.4 and one akaline with a pH of 8.7. For
each case three trajectories are shown: the 700 mb (indicated by U), 850 mb (M)
and 1OOOmb (L) level. In the first case the trajectories
of 3 February 1980 at
12.00 GMT and the other four which precede them pass over Northeast Europe
on their way to Israel, In the high pH case, it is rather evident that trajectories
passed over the North African and Saharan deserts, picking up alkaline material.
CONCLUSIONS
The combination
of backward air trajectories
at three elevations and the
chemistry of bulk precipitation
enables us to identify the main sources of
alkaline and acidic rain events in Israel. The alkaline sources were, as expected, associated with the deserts along the North African continent,
which
provide calcites and other soluble carbonates, and thus control the rain chemistry. The acidic sources were associated with trajectories
arriving from
Northeast
Europe. Industrial
emissions of sulfur and nitrogen oxides from
these regions, as well as the absence of buffering alkaline material in the air,
resulted in the rain being acidic. Trajectory analyses provide direct evidence
for the long-range transport of acidic emissions to the Eastern Mediterranean.
This type of flow, however, is less frequent during the winter months, less than
20% of all winter trajectories (Dayan, 1986).
Acidic
pti
Case
=
Co*+=
Alkaline
Case
4.4
25
NO;
=
59
so;
=
89
No*
=
257
ASIA
Fig. 2. Trajectories
of two extreme
cases: acidic
from northeast
Europe,
while in the latter they
and alkaline
cross North
rain.
Africa
In the former
trajectories
arrive
carrying
desert dust with them.
21
Since most of the trajectories cross the Mediterranean
in sea salt components such as chlorides and sulfates
and potassium.
Sea, the rain was rich
of sodium, magnesium
ACKNOWLEDGEMENTS
The authors acknowledge the assistance of the Israeli Meteorological
Service, and especially of Mr A. Manes for establishing the rain network and the
collection of rain samples and Mrs E. Melamed for the chemical analyses.
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