Acidification and Arctic Haze - The Changing Arctic Environment: The Arctic Messenger - page 84

6 Acidification and Arctic Haze
Casca: “I durst not laugh for fear of opening my lips and receiving the bad air.”
William Shakespeare, Julius Caesar
Before we start, here is another simple revision of our school chemistry. Water molecules
exist in equilibrium with hydrogen ions H + and hydroxide ions OH - .
H 2 O <-> H + + OH −
A solution is acidic if the H + ions are in excess and is basic (or alkaline) if the OH - ions
are in excess. The pH scale is used to measure the acidity of a substance. The scale ranges
from 0 to 14. A pH value of 7 is neutral. A value of less than 7 is acidic and a value greater
than 7 is basic. It is a logarithmic scale. Therefore, pH 5 is 10 times more acidic than pH 6
and 100 times more acidic than the neutral pH 7. Normal rain has a pH of about 5.6 due to
an interaction with carbon dioxide, which results in the formation of carbonic acid.
With this technicality over, the acidification story can begin. In Part 1, we briefly noted
that in the 1960s, terrestrial and freshwater ecologists began to describe widespread deteri-
oration of forests and freshwater ecosystems in northern Europe, eastern Canada, and north-
eastern United States. The cause was quickly identified. Sulphur and nitrogen oxides re-
leased from combustion sources were reacting with water in the atmosphere to form acids
of nitrogen and sulphur that increased the acidity of rain and snow. It was probably the first
time the general public heard the phrase acid rain .
It is worth pausing for a moment to appreciate several of the then-unique features of
this situation. First, the sources of the offending sulphur and nitrogen were ubiquitous and
included nonferrous metal smelting and the combustion of hydrocarbons, ranging in scope
from industrial scale activities (including electrical power generation) to automobile exhaust
andalsoatthattimefromdomesticheating.Coalwasaparticularlysignificantsource.When
I was a child in the south-east of England in the 1950s, I remember the dense, suffocating
winter smog that hung over London whenever my parents would take me to the city. Thou-
sands of people died at this time from respiratory complications in the large industrial cities