Ten. sampling sites spread across the
Sydney metropolitan area were
employed, and two in the Blue
Mountains.
Rain brought by onshore
winds was more acidic than
that brought by offshore
winds.
b u t i o n o f the p H o f t h e s e s a m p l e s . M o s t o f
the rain-water c o l l e c t e d h a d a p H b e l o w
5 • 2 , a n d c o u l d therefore b e l a b e l l e d as
Sydney's rain reaches its highest acid level at this time
of year, 1 0 - 1 5 times greater than that in unpolluted rain­
water.
a c i d i c r a i n . A s a m p l e c o l l e c t e d at E p p i n g
g a v e the m o s t a c i d r e a d i n g ( p H 3 • 6 ) .
T h e s a m p l e s w i t h the l o w e s t a c i d i t y
(highest p H values) c a m e from Loftus, a
site that l i e s u p w i n d o f the c i t y d u r i n g the
o f rain acidity by D r
w o r k i n g at the D i v i s i o n o f A t m o s p h e r i c
south-easterly
G r e g A y e r s a n d M r R o b G i l l e t t , o f CSIRO,
P h y s i c s i n M e l b o u r n e , a l l o w i n g t h e study
Sydney's summer
s h o w that S y d n e y rain o v e r the past t w o
to b e e x t e n d e d to that city.
Loftus samples averaged 5 • 0 8 .
Measurements
s u m m e r s h a s h a d a n average p H o f a b o u t
T h e S y d n e y results s h o w that the c i t y
w i n d s that b r i n g m o s t o f
rain. T h e p H o f the
Wind influence
4•5. T h i s compares with a p H o f about
s h a r e s w i t h its N o r t h e r n
5 • 2 for rain-water u n a f f e c t e d b y c i t y e m i s ­
c o u n t e r p a r t s the ability, i n s u m m e r
s i o n s (it c a n r a n g e f r o m 4 • 8 to 5 • 8 ) . T h e
least, to p r o d u c e s i g n i f i c a n t l e v e l s o f r a i n ­
several years a g o b y D r W i l l i a m S c o t t ,
l o w e s t p H s o far o b s e r v e d i n the S y d n e y
w a t e r a c i d i t y . I n the w o r s t - a f f e c t e d
re­
then in the D i v i s i o n o f C l o u d Physics,
studies w a s 3 • 6 , as a c i d i c as o r a n g e j u i c e .
g i o n s o f the n o r t h - e a s t e r n U n i t e d States,
w h i c h i m p l i c a t e d the S y d n e y m e t r o p o l i ­
' A c i d rain' m a i n l y d e v e l o p s b e c a u s e o f
annual mean p H values o f 4 • 0 have been
tan area as a s o u r c e o f a c i d i t y .
Taking
the p r e s e n c e o f sulfuric a n d n i t r i c a c i d s
observed, compared with about 4 • 6
s a m p l e s f r o m a n aircraft f l y i n g
through
— p r o d u c e d b y e m i s s i o n s o f sulfur d i o x ­
Sydney.
Hemisphere
at
in
T h e h i g h e r v a l u e s at L o f t u s c o n f i r m w o r k
c l o u d , D r S c o t t f o u n d that t h e m e a n p H o f
D r A y e r s b e l i e v e s that, j u d g i n g b y e x ­
ten c l o u d s u p w i n d o f the c i t y w a s 6 • 2 ,
p e r i e n c e e l s e w h e r e i n the w o r l d , this l e v e l
w h e r e a s the c o r r e s p o n d i n g figure for three
It is c a u s i n g g r o w i n g c o n c e r n i n E u r o p e
is n o t l i k e l y t o l e a d t o o b v i o u s e n v i r o n ­
clouds d o w n w i n d was 4 • 9 .
and N o r t h A m e r i c a , w h e r e it is b l a m e d for
mental damage. Possibly, s u c h acid levels
killing fish in lakes, r e d u c i n g
forest
in s u m m e r c o u l d i n c r e a s e the c o r r o s i o n o f
ural a t m o s p h e r i c
growth, and leaching metals f r o m soils
steel, m a s o n r y , and other e x p o s e d surfaces.
a c i d i t y o f the rain t o o . T h e i r data s h o w e d
into groundwater in e c o l o g i c a l l y harmful
M o s t o f the s a m p l i n g t o o k p l a c e i n the
that rain b r o u g h t by o n s h o r e w i n d s w a s ,
c o n c e n t r a t i o n s . H o w e v e r , there h a s b e e n
s u m m e r o f 1 9 8 0 / 8 1 , w h e n 2 9 4 rain s a m ­
o n a v e r a g e , s i g n i f i c a n t l y m o r e a c i d i c than
hardly any interest i n a c i d i c rain i n A u s ­
p l e s w e r e c o l l e c t e d f r o m 12 sites a c r o s s
that b r o u g h t b y o f f s h o r e w i n d s .
tralia, b e c a u s e w e t h o u g h t that n e i t h e r
S y d n e y . A p a r t f r o m t h o s e taken at
the
T h i s d i f f e r e n c e reflects the fact that the
our population nor our industry was o n a
D i v i s i o n ' s site at E p p i n g , s a m p l e s w e r e
c o n t i n e n t is a larger s o u r c e o f alkaline
i d e a n d n i t r o g e n o x i d e s f r o m p o w e r sta­
tions, industries, and m o t o r v e h i c l e s .
b i g e n o u g h s c a l e to c a u s e p r o b l e m s .
D r A y e r s a n d M r G i l l e t t f o u n d that nat­
p r o c e s s e s affect
the
c o l l e c t e d b y c o l l e a g u e s at their h o m e s
m a t e r i a l s i n the a t m o s p h e r e ( g a s e o u s a m ­
D r A y e r s , o f the D i v i s i o n o f C l o u d
w h e n e v e r it r a i n e d , a n d b r o u g h t i n for
m o n i a f r o m d e c a y i n g o r g a n i c materials,
P h y s i c s at E p p i n g i n S y d n e y , is c u r r e n t l y
analysis. T h e d i a g r a m s h o w s the distri-
a n d c a l c a r e o u s d u s t p a r t i c l e s ) t h a n the
21
The pH scale
I n an a c i d s o l u t i o n , the h y d r o n i u m i o n s
p r e d o m i n a t e a n d the p H is l e s s t h a n 7 —
the s t r o n g e r the a c i d is, the s m a l l e r its p H
v a l u e . E a c h step i n the p H s c a l e c o r r e s ­
p o n d s to a c h a n g e i n the c o n c e n t r a t i o n o f
the a c i d i o n b y a factor o f 10. O n the other
hand, alkaline solutions have p H values
above 7.
T h e p H o f rain-water is g e n e r a l l y b e l o w
I n any w a t e r - b a s e d s o l u t i o n , the c o n c e n ­
7 w h e t h e r o r n o t a c i t y ' s e m i s s i o n s have
tration o f a c i d h y d r o n i u m i o n s ( H
affected it. T h i s is b e c a u s e c a r b o n d i o x i d e
+
or
H O ) is i n b a l a n c e w i t h that o f t h e alka­
a n d o t h e r natural c o n s t i t u t e n t s o f the at­
line hydroxyl i o n O H " .
m o s p h e r e h a v e an a c i d i f y i n g i n f l u e n c e o n
+
3
I n p u r e water, the a c i d a n d
alkaline
species have equal concentrations,
and
the p H = 7 .
it.
T h e table s h o w s p H r e a d i n g s for var­
substance
hydrochloric acid,
1 M
lime juice
orange juice
rhubarb
carbonated water
tomatoes
boric acid, 0•1 M
coW s milk
distilled water
egg white
borax, 0•1 M
ammonia, 1 M
sodium hydroxide,
1M
pH
01
1•8—2-0
3•0—4-0
3•1-3-2
3•8
4•0—4-4
5•2
6•3—6•6
7•0
7•6-8•0
9•2
11-6
acidic
neutral
alkaline
14•0
ious well-known solutions.
The mean p H of the samples varied
month by month. The most acidic rain
fell in summer; readings closer to
neutral were obtained in spring.
o c e a n . P e r i o d i c a l l y , these h i g h e r
quan­
tities o f a l k a l i n e materials g i v e rise t o p H
v a l u e s greater than 6, s u c h as t h o s e o b ­
served u p w i n d o f S y d n e y b y D r S c o t t .
T h e researchers
also analysed
their
s a m p l e s for a m m o n i a , sulfate, a n d nitrate.
T h e i r r e s u l t s i n d i c a t e d that n i t r i c a n d sul­
furic a c i d s are m a i n l y to b l a m e for the
acidity. W i t h o u t these a c i d s , S y d n e y s u m ­
m e r rain w o u l d have a p H o f a b o u t 5 • 2 ,
they c a l c u l a t e d . A d d i n g w e i g h t to the re­
liability o f this estimate, f o u r s a m p l e s o f
rain-water c o l l e c t e d 2 7 0 k m s o u t h o f Syd­
An ion chromatograph was used to
analyse samples of Sydney's rain.
t i n u e d f r o m the s u m m e r o f 1 9 8 0 / 8 1 to the
f o l l o w i n g s u m m e r . T h e data s h o w e d that
ney during onshore winds s h o w e d a mean
s u m m e r i n d e e d b r i n g s the m o s t a c i d i c
p H o f exactly 5•2.
r a i n ; p H v a l u e s c l o s e r to neutral w e r e o b ­
tained i n spring (see the g r a p h ) . T h e s e
T h e r e s e a r c h pair f o u n d that rain-water
sites also had a m e a n p H 0 • 28 units higher
f r o m c l o u d s that passed o v e r S y d n e y re­
m a i n e d a c i d i c for s o m e t i m e . S i t e s
in the s e c o n d s u m m e r than i n the first.
at
M r G i l l e t t is c o n t i n u i n g to m o n i t o r acid
W a r r i m o o a n d S p r i n g w o o d i n the B l u e
(60—70 k m inland) s h o w e d
l e v e l s at the E p p i n g and W a r r i m o o sites,
e s s e n t i a l l y the s a m e p H l e v e l s as all the
w h i l e D r A y e r s takes s o m e m e a s u r e m e n t s
o t h e r s ( e x c e p t i n g the o n e at L o f t u s ) .
o n the a c i d i t y o f M e l b o u r n e ' s rain.
Mountains
Andrew
A t three o f the sites ( W a r r i m o o , H o r n s b y
H e i g h t s , and E p p i n g ) , sampling was c o n -
Bell
M o r e about the topic
A c i d i t y o f s u m m e r rainfall i n S y d n e y . G . P .
The lowest pH was 3•6, as
acidic as orange juice.
22
M o s t of the rain had a p H below 5 •2,
and could therefore be labelled as
acidic. The most acidic had a
p H of 3 • 6 .
Ayers and R . W . Gillett. In ' T h e Urban
A t m o s p h e r e — Sydney, a Case Study',
ed. J.N. Carras and
G . M . Johnson.
( C S I R O : M e l b o u r n e , i n press.)