What about nitrogen?
Although the amount of sulphur dioxide that is being released has been cut considerably, more needs to be done about nitrogen oxide from motor vehicles and agricultural fertilizers. When nitrogen oxide mixes with rain it forms nitric acid which drains important plant nutrients from the soil and releases minerals such as aluminium into water courses.
Too much nitrogen in our waterways can lead to eutrophication. This is when algal blooms or just a few dominant plant species take over and block all the light for underwater plants. When the algae dies and starts to decompose, tiny decomposing organisms use up all the oxygen, leaving none for other aquatic creatures.