occurrence

Since the mid-1980s, when Indonesia first began to clear its bountiful forests on an industrial scale in favour of lucrative palm-oil plantations, “haze” has become an almost annual occurrence in South-East Asia. The cheapest way to clear logged woodland is to burn it, producing an acrid cloud of foul white smoke that, carried by the wind, can cover hundreds, or even thousands, of square miles.

The time interval of an occurrence—a temporal instantiation—is a single occasion. However, a series of such occasions can fall within a certain time interval; in this case we may represent the occurrence as a single situation (cf. I ran off and on for an hour, I ran and ran for an hour, I would run and then run some more).