In winter of course healthy and sick ash trees are difficult to tell apart as the leaves will all have fallen to the ground.

BBC: The heartbreak of watching the slow death of ash trees

Modern industry produces many things, from coal ash to computers, that are difficult to dispose of properly.

ECONOMIST: The waste industry

Gauging the economic impact of the crisis is as difficult as predicting when and where the next cloud of ash will appear.

ECONOMIST: The effect on business and leisure