On Monday, choking smog in China’s northern city of Harbin in Heilongjiang province forced the city to shut down its roads, airports, and schools. Officials blamed the severe pollution on the city’s switch to the coal-heating system for winter months, farmers burning crop stubble, and low winds. PM2.5, a scale used to measure airborne particles considered most harmful to health, showed readings of over 500 micrograms per cubic meter on Monday morning, reaching 1000 in some parts of the city. According to World Health Organization, average daily concentrations of PM2.5 exceeding 25 micrograms per cubic meter are considered unhealthy. Visibility was reportedly reduced to below 160 feet. This week, officials announced emergency measures to tackle the pressing pollution, including mandatory factory closures and bans on cars entering the city on days when pollution levels are high. (National Geographic, Oct 22; BBC, CNN, Oct 23, 2013)