(Image source: Twitter / Xinhua News )     BY ZACH TOOMBS     When Beijing sounds the alarm on hazardous pollution levels, you know it’s bad.   Beijing’s municipal monitoring center has advised the elderly and children to remain indoors over the next three days, as pollution levels in the notoriously smoggy Chinese capital have climbed into especially dangerous territory. [Video: BBC ]   Sky News’ Mark Stone gives a look from street level.   “Beijing is effectively built in a desert. And around the city center itself are hundreds of factories churning out pretty bad stuff, and this is the result.”   But as for just how bad those pollution levels are — well, that depends on who you ask.   Pollution is measured in micrograms per cubic meter. In New York and London, that figure is typically under 15. Saturday in Beijing, Chinese officials pegged it at over 400 — the worst since the city started recording data a year ago. But the American embassy’s monitoring unit reports levels above 800. [Video: RT ]   Anything above 300 is considered hazardous — enough to keep the vulnerable and those with respiratory problems indoors for days. An ever-growing number of cars in the city of 20 million people is largely to blame — as are the factories that line Beijing, which has seen booming industrial growth over the past 30 years. [Video: NTDTV ]   But while China’s government admitted to hazardous pollution levels, Western observers pointed out its state-run Xinhua news agency tried to pass off the haze as bad weather.   In its headline, Xinhua says fog is the cause of grounded flights across eastern China, then refers to it as “smoggy weather.” In an accompanying photo slideshow, again “fog,” not smog, was to blame for conditions in Beijing.   China’s pollution problem is about more than delays at airports and limited visibility at street level. Last year, researchers at Columbia University told NPR that life in Beijing could, on average, take five years off your lifespan — as compared to living in China’s southern cities.   In all, health risks include a heightened chance of contracting respiratory illnesses, heart disease and lung cancer.