City applies high technology to anti-pollution battle

Some Beijing residents use smokestacks to predict smog: Smoke drifting gently upward means stagnant air where smog will accumulate, while smoke blowing away from the mountains indicates fresher winds and clear air ahead.

But the city government uses more sophisticated technology for its forecasts, including the one used this week to trigger Beijing's first-ever red alert for smog. The alert brought restrictions on cars and factories, as well as other measures aimed at keeping the smog in check.

The system takes into account not only weather patterns that suspend pollutants in the air, but also industry emissions and flows of vehicles and their emissions.