On Monday, the Chinese city of Beijing issued its first "red alert" for air pollution, meaning officials have forecasted more than three consecutive days of severe smog for the area, the Associated Press reports. The alert, which was upgraded from orange, will stay in effect from Monday through Thursday, according to an online notice from the Beijing Municipal Environmental Protection Bureau. During that time, outdoor construction will come to a halt, half of the city's vehicles will be banned from the roads, and many schools will close or cancel classes.
The red alert is based on this week's forecast for Beijing's PM2.5 levels, which denote the amount of fine particulate matter in the air. These tiny particles are referred to as PM2.5, because they are less than 2.5 micrometers across — between 30 and 100 times thinner than a human hair. PM2.5 are thought to pose the greatest risk to human health, since they can be inhaled and then lodge inside a person's lungs. Exposure to these particles — which are produced by vehicle exhaust, coal-fired power plants, and other industrial work — has been linked with aggravated asthma, irregular heartbeat, and an increase in respiratory problems.
The alert will stay in effect from Monday through Thursday
Air monitoring in Beijing measured PM2.5 levels climbing toward 300 micrograms per cubic meter on Monday, and they're expected to get worse throughout the week. PM2.5 levels are considered safe at 25 micrograms per cubic meter; cities issue red alerts when PM2.5 levels are expected to exceed 200 micrograms per cubic meter for more than 72 consecutive hours. Officials think that an incoming cold front on Thursday will clear the smog and lower the alert level.
This isn't the first time a Chinese city has declared a red alert for air pollution, nor is it the first time Beijing has experienced a prolonged period of severe smog. Earlier this month, PM2.5 levels in the city's suburbs measured as high as 976 micrograms per cubic meter. China has taken steps to combat the nation's extensive smog problem, such as reducing its reliance on coal power and improving public transportation. The country also announced in June that it would cap its CO2 emissions starting in 2016. China's government has also set up a rigorous air pollution reporting system to monitor the issue in real time.
Using data from this system, Berkeley Earth released a report in August showing that air pollution is responsible for 17 percent of all deaths in China.