Measuring Acid Rain
The pH (not PH) scale is used to measure the acidity or alkalinity of
an aqueous solution and is determined by the hydrogen ion content (H+).
This scale was invented by a Danish scientist called Sorenson in 1909.
The pH scale ranges from 0, which is strongly acid, to 14 which is
strongly alkaline, the scale point 7 being neutral. Examples of
solutions with differing pH values include car battery acid (pH 1),
lemon juice (pH 2), beer (pH 4), natural rain (pH 5-6), milk (pH 6),
washing-up liquid (pH 7), seawater (pH 8), milk of magnesia (pH 10) and
ammonia (pH 12),
The pH scale is logarithmic rather than linear, and so there is a ten
fold increase in acidity with each pH unit, such that rainfall with pH 5
is ten times more acidic than pH 6, rainfall with pH 4 is 100 times
more acidic than pH 6 and rainfall with pH 3 is 1000 times more acidic
than pH 6.
Rainfall acidity is measured in pH units. �Normal� or �unpolluted�
rainfall has a pH of 5.6. This is slightly acidic due to the presence of
carbon dioxide in the atmosphere which forms weak carbonic acid in
water. It is not uncommon for acidified rainwater to have a pH of 4,
about 30 times as acidic as normal rainwater.
