§ Mr. BerminghamTo ask the Secretary of State for the Environment if he will list the total number of photochemical smog events which have occurred during the last year in England and Wales; and if he will make a statement.
§ Mr. Heathcoat-Amory[holding answer 30 October 1989]: Photochemical smog, consisting of ozone and other ingredients, is a result of the reaction between oxides of nitrogen and gaseous hydrocarbons in the presence of sunlight. In the United Kingdom a network of 17 sites monitors ozone levels. There is always some ozone in the lower atmosphere, and the definition of an "event" is inevitably arbitary. However, in August my Department announced that it would issue daily summaries of ozone 123W concentrations for periods when several network sites recorded an hourly average of 60 parts per billion or more. Since then there have been three such periods. The record for the period before August shows a further five periods during the last year.