On Tuesday, a blanket of humid air trapping smog brought Beijing’s first pollution “red alert.” Many residents ignored warnings to limit time outdoors, and authorities say the pollution would last several more days. Hundreds of people, even babies, packed Tiananmen Square to watch a daily flag-raising ceremony. China’s state radio said some motorists were ignoring a ban on vehicles bearing odd-numbered license plates. Rapid industrial growth and car ownership over the past decade caused high levels of pollution in major urban areas and Chinese researches have identified the problem as a major source of unrest. Weather conditions like “still air” can make the problem worse.