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“Usually one thinks about pollutants such as nitrogen dioxide and nitrous acid as being lost from the atmosphere onto surfaces.”

When intense, as they are at present, they produce ozone in great quantity, and also, as Professor Crookes has pointed out, nitrous acid.

Nitric and nitrous acids are also produced by electric discharges through the atmosphere, and these are found eventually as nitrates in soils, &c.

The nitrous acid dissolves copper with most rapidity, producing nitrous air.

There was still, however, the production of the volatile alkali and of nitrous acid to be accounted for.