Polluting factories have been moved or closed. But auto emissions are rising as the city adds up to 1,200 new cars and trucks every day. Dirty, coal-burning furnaces have been replaced, lowering the city’s sulfur dioxide emissions. But fine-particle pollution has been exacerbated by a staggering citywide construction binge that shows no signs of letting up.

China’s unsolved riddle is how to reconcile fast economic growth with environmental protection. But Beijing’s Olympic deadline means the city needs an immediate answer. The ruling Communist Party envisions the Games as a public relations showcase and is leaving no detail untended. Scientists are cross-breeding chrysanthemums to ensure that flowers bloom in August.

Now Beijing is also going to try to manipulate air quality. For months, scientists have treated the city like a laboratory, testing wind patterns and atmospheric structure, while pinpointing local and regional pollution sources. Olympics contingency plans have been approved for Beijing and surrounding provinces. Details are not public, but officials have discussed shutting down factories and restricting traffic during the Games.

“We are determined to ensure that the air conditions meet the necessary standards in August 2008,” Liu Qi, president of the Beijing Organizing Committee for the Games, told the International Olympic Committee’s executive board this month.