PARIS — As an increasingly large part of European airspace was shut down for the third day on Saturday and the towering fountain of ash from an Icelandic volcano showed no signs of letting up, questions about the long-term impact of the eruption were being raised in a continent trying to recover from recession.
Officials expressed hope that some air travel could resume today, or possibly Monday, but the workings of Iceland's volcano were too mysterious to make rational predictions. Winds pushed the particulate ash farther south and east on Saturday, as far as northern Italy.
About 17,000 flights were canceled on Saturday, and travelers scrambled to find accommodation or land routes home during what is already the worst disruption in international air travel since the attacks of Sept. 11, 2001, when all air travel in and out of the United States was halted for three days.
While the closing of the airways has already laid waste to the immediate plans and business of industry, the arts and world leaders, the possibility that it could drag on for days, if not weeks, is raising concerns about the longer term consequences for public health, military operations and the world economy.
The airline industry was the first economic casualty. Steve Lott, a spokesman for the International Air Transport Association, said that with the conservative estimate of $200 million loss in revenue per day, "we could easily hit a billion dollars loss in revenue next week."
The economic damage will roll through to farms, retail establishments and nearly any other business that depends on air-cargo shipments. Fresh produce will spoil, and supermarkets in Europe, used to year-round supplies, will begin to run out.
But unless flights are disrupted for weeks, threatening factories' supply chains, economists do not think the crisis will significantly affect gross domestic product.
The shutdown has also affected American military operations. Military supplies for operations in Afghanistan have been disrupted, and a spokeswoman for the Pentagon said that all medical evacuation flights from Iraq and Afghanistan to Germany, where most injured soldiers are typically treated, were being diverted directly to Andrews Air Force Base in Maryland.
Within the European Command, some routine resupply missions and movement of personnel missions have been diverted or delayed, she said.
The World Health Organization issued an advisory saying that as long as the ash remains in the upper atmosphere, there is not likely to be increased health risk.
So far, analysis of the ash shows that about a quarter of the particles are smaller than 10 microns, making them more dangerous because they can penetrate more deeply into the lungs, WHO said.
In Britain, where a layer of fine dust is already covering large swaths of the country, the authorities are advising those with respiratory problems to stay indoors or wear masks out of doors.
But experts said most people had no reason to be alarmed. "The bottom line," said Dr. Ronald Crystal, chief of pulmonology at New York Presbyterian/Weill Cornell hospital, "is there's no long-term health effect from volcanic ash."
International transportation, however, was still what the front page of the French newspaper Le Parisien called "La Grande Pagaille" — the big mess.
The ash cloud also scuttled routine diplomacy, an effect most evident in the dwindling guest list of dignitaries planning to attend the state funeral today for President Lech Kaczynski of Poland and his wife, who died in a plane crash April 10. On Saturday, at least a dozen delegations canceled plans to attend, including those of President Barack Obama, Chancellor Angela Merkel of Germany and Prince Charles of Britain.
President Valdis Zatlers of Latvia embarked Saturday on a 14-hour car trip so he could attend.
At least one major airline, Lufthansa, expressed frustration at what it suggested was excessive caution by the German authorities, who kept every German airport closed to air traffic for a second day.
But German officials defended their decision. "What's more important, the safety of passengers or business?" asked Helmut Malewski, a meteorologist at the German Weather Service. "We're erring on the side of safety."
The volcano, meanwhile, continued to defy predictions. Clive Oppenheimer, a volcanologist at the University of Cambridge, said the average span of a volcanic eruption is a month or two.
In the case of Iceland's Eyjafjallajokull volcano, he said, scientists need to know more about how much molten rock is beneath it, but concluded, "We could see intermittent activity over the coming months."
But Leo Liao, a Hong Kong businessman who was stranded at the Frankfurt airport, was cheerful and philosophical. "It's a natural issue," he said. "Never complain. You can't change this."