Pollutionwatch: how sources of summertime smog are changing
Increases in methane from fracking, agriculture and gas production are adding to our climate emergency
On 26 July 1943, at the height of the second world war, people in Los Angeles thought they were under chemical gas attack as they experienced stinging eyes and rasping throats in what is now recognised as the first summer smogs. Once synonymous with Los Angeles, this is now known to be a serious problem in much cooler climates, including the UK. These smogs come from chemical reactions between a cocktail of pollutants over several days, driven by sunlight. One of the main pollutants is ozone. In the upper atmosphere it shields us from harmful ultraviolet light, but when breathed it is very harmful.
Ozone is very chemically reactive. Early measurement methods in Los Angeles included placing stretched rubber tubes outside every hour and waiting until cracks appeared. Sometimes it took as little as six minutes.