Beijing ( CNN ) -- Schoolchildren were ordered to halt outdoor sports activities until Tuesday this week , as a dirty cloud of smog continued to shroud China 's capital . This was among a series of emergency response measures adopted in Beijing Sunday when the city 's Air Quality Index exceeded 500 micrograms , the highest level . Anything above this is regarded as `` beyond index . '' Reports of respiratory problems -- as well as the sale of masks -- have skyrocketed , according to state media , and over the weekend , streets appeared emptier , as a sun was barely visible amid a hazy blanket . On Monday morning the U.S. Embassy in Beijing recorded `` hazardous '' levels of pollution , with a `` Beyond Index '' reading of 515 at 3:00 a.m. ( 2 p.m. Sunday ) local time , last seen on Saturday when the air quality index , based on U.S. national air quality standards , hit as high as 755 . Read more : Which city has best quality of life ? Beijing Hyundai Motor Company suspended production on Sunday , and nearly 30 construction sites halted construction , the China Daily cited the city 's environmental protection bureau as saying . The city 's residents say pollution is worsening despite authorities ' assertions that air quality has improved since the city hosted the 2008 Olympic Games . Last year , heavy haze and smog forced the cancellation of almost 700 flights at Beijing airports . The city is comparable to Los Angeles , another gray city , according to experts . `` With their difficult meteorological conditions and a large number of pollution sources , addressing pollution is a long-term and difficult task , '' Deborah Seligsohn , adviser of the World Resources Institute , said last year . The agency runs a climate energy and pollution program in China . Los Angeles has battled air pollution since the 1950s , well before U.S. national regulation , according to Seligsohn . `` Stilll in the 1970s , 20 years later , it was famous for its smog , '' she said . `` In the 40-plus years since the Clean Air Act was passed , L.A. has never been fully in compliance with EPA standards , even though it has continued to improve . '' Read more : China must come clean on pollution . European Commission figures show that China produced 9.7 million kilotons of carbon dioxide while the United States had 5.42 million kilotons in 2011 , the latest available numbers . The weekend 's pollution levels have prompted an `` orange fog '' warning in Beijing because of diminished visibility , according to state-run Xinhua news agency . `` Pollutants have gradually accumulated over the course of recent windless days , making the air quality even worse , '' said Zhu Tong , an environmental sciences professor at Peking University told news agency . Beijing will remain covered in gray until Wednesday , when the wind will sweep in to the rescue and blow the smog away , according to state media . CY Xu in Beijing and Faith Karimi in Atlanta contributed to this report .
NEW : Beijing recording ` ` hazardous '' levels of air pollution ' . NEW : Children in worst - affected areas ordered to stop outdoor sports activities . Reports of respiratory problems -- and sale of masks -- skyrocket . U.S. Embassy in Beijing reports an exposure of more than 700 micrograms daily .