Smog in Paris Rivals Beijing's

Air pollution that has turned the skies over Paris a murky yellow and shrouded much of Belgium for days forced drivers to slow down today and gave millions a free ride on public transportation. The belt of smog stretched for hundreds of miles, from France's Atlantic coast to Belgium and well into Germany. It was the worst air pollution France has seen since 2007, the European Environment Agency said. Nearly all of France was under some sort of pollution alert, with levels in the Parisian region surpassing some of those in the world's most notoriously polluted cities, including Beijing and Delhi.

Smog isn't unheard of in Paris, of course, but it's rare for it to be this severe and this prolonged, especially so early in the year, reports the New York Times. France has an unusually high number of diesel vehicles, whose nitrogen oxide fumes mix with ammonia from springtime fertilizers and form particulate ammonium nitrate. Pollutants from the burning of dead leaves and wood contribute as well. One environmental group complained earlier this week, denouncing the "inertia of the government" and saying it was putting lives in danger. The European Commission, meanwhile, has criticized France multiple times for not complying with Europe's pollution rules. (Click to read about how a scientist in China likened the situation there to "nuclear winter.")