The erupting volcano on La Palma in the Canary Islands has brought a new and unwelcome weather effect: vog, or volcanic smog.
Vog is a regular occurrence in areas with frequent volcanic activity such as Hawaii and so has been studied extensively. While urban smog is generated by ozone and nitrogen oxides, vog occurs when sulphur dioxide gas and other volcanic emissions react with water and oxygen in the air.
Fog is composed of water droplets, but the droplets in vog are dilute sulphuric acid. At higher levels even healthy people may find breathing difficult in vog, and lower concentrations can be unpleasant and unhealthy to breathe.
Vog causes eye and throat irritation, coughing and increased susceptibility to respiratory conditions. It is particularly dangerous to asthma sufferers as it can cause tightening of the airways and bring on symptoms. It may also be hazardous for older people and small children.
Those most at risk are advised to stay indoors with doors and windows closed. Air conditioners or dehumidifiers may help, as these condense water out of the air, extracting some of the more harmful substances in vog.
Fortunately, vog dissipates in time with wind and rain. Although it is unpleasant, studies have not yet found any evidence that vog exposure causes long-term health effects.
