A fire at an Iraq chemical plant has caused the largest recorded man-made release of sulphur dioxide, experts say
The fire, which broke out on 24 June 2003, produced more of the polluting gas than most volcanic eruptions.
On average it generated about 21,000 tonnes of sulphur dioxide a day, which is half the daily emissions of the gas produced by the United States.
The plume of smog was detected by a Nasa satellite, the researchers say in Geophysical Research Letters.
The fire, which was probably started deliberately, broke out at the Al-Mishraq state sulphur plant near Mosul. It burned for almost a month.
Scientists monitored the blaze using satellite images. They calculated that a total of around 600,000 tonnes of sulphur dioxide was released by the fire.
To put that figure in context, the giant eruption of the US volcano Mount St Helens in 1980 belched out about one million tonnes of sulphur dioxide.
Although the team, from the University of Maryland in Baltimore, believes the fire will not have a long-lasting environmental impact, it says the fire caused about $40m of damage to local crops - along with respiratory problems in local people.
The scientists used two instruments to collect the data - the Total Ozone Mapping Spectrometer and Moderate Resolution Imaging Spectroradiometer - which are located on Nasa's Earth monitoring satellites Terra and Aqua.