Beijing's new top official vowed to tackle the city's smog problem, a simmering cause of discontent among China's expanding middle class.

Cai Qi, the Communist Party chief in the capital, told a gathering of local delegates Monday that the metropolis of 22 million must slash pollution levels to "win the battle against pollution." He pledged to cut levels of the most hazardous airborne particulate by 30 percent over the next five years, while pushing polluters and "nonessential" services out to "display the image of a major country's capital city."

The speech to Beijing's municipal party congress — one of dozens of regional meetings being held ahead of a planned reshuffle of the national leadership later this year — comes less than a month after Cai's promotion. A former subordinate of President Xi Jinping, Cai, 61, is among the local leaders being watched for possible advancement at the upcoming gathering, in which scores of top political officials are expected to be replaced.