What happened

As the battle of Mosul intensified, Islamic State fighters set fire to the Al-Mishraq sulfur production complex, releasing an estimated 161 kilotonnes of sulfur dioxide over about a week — comparable to a minor volcanic eruption and tracked by multiple satellites (MetOp-A/B, Aura, Suomi NPP). Two civilians died and nearly 1,000 people were treated for toxic gas inhalation from the sulfur dioxide and hydrogen sulphide plume.

When cited sources give different casualty, damage or spill figures for this event, they’re reported side by side above rather than merged into one number. See how confidence levels work.