The Turrialba volcano erupted again Monday afternoon, and officials at Juan Santamaría airport quickly halted flights.
The Red Sismológica Nacional said the eruption lasted about 20 minutes after starting at 3:19 p.m.
The national emergency commission said that the winds carried the ash once again into the metro area. There were reports of a layer of ash in parts of San José. As in the past, the distribution of ash was mostly to the northern part of the Central Valley.
The Alajuela airport was expected to reopen at 6 a.m. today. Some incoming flights were diverted and others were canceled.
This is the third time that the airport shut down. In addition to coating the runways, the ash can cause damage to jet turbine engines. The last shutdown was for about 18 hours April 23 and 24.
Scientists at the Red Sismológica Nacional said they were monitoring the mountain closely because they expected more activity.
Residents in the area posted eruption photos on the Web site of the Red.