Beijing advised the young, elderly and ill among its 20 million residents to reduce time spent outdoors as a U.S. Embassy pollution monitor showed air quality in the Chinese capital at “heavily polluted” levels today.

Concentrations of PM2.5, fine air particulates that pose the greatest health risk, rose to 241 micrograms per cubic meter as of noontime near Tiananmen Square from an average of 124 in the past 24 hours, according to the Beijing Municipal Environmental Monitoring Center. This compares with the World Health Organization’s recommendation of no higher than 25 for day-long exposure.

Chinese authorities have taken steps to curb the burning of coal and reduce car traffic to assuage public anger sparked by dirty air and water. Beijing Communist Party Secretary Guo Jinlong, the city administration’s highest ranking official, pledged this week to improve air quality, telling a meeting of municipal officials that controlling pollution is in the people’s interests, consistent with Beijing’s development and China’s national image, the Beijing Times reported today.

The Beijing Meteorological Bureau also issued a warning on its official microblog today for residents to drive safely as rain and haze reduce visibility.