The Popocatepetl Volcano close to Mexico City erupted again yesterday and ash fell on parts of the capital and nearby towns causing some airlines to cancel flights.

An official from the Mexico City international airport told the TV Azteca network that United Airlines and other international carriers had canceled flights after a light ash fell in the area. But most airlines continued flying into the airport.
http://news.airwise.com/stories/2000/12/976881352.html