The air pollution has gotten so bad in Beijing, that the city issued a rare air pollution alert.

Beijing had recorded extremely poisonous air pollution in January and this week, it's back and is expected to continue for several days at dangerous levels.

On Friday, an "orange" alert was issued, the second-highest alert in the four levels. The warning calls for health advisories and bans on barbeques, fireworks and demolition work. The city says it has a plan to try to take half of the city's cars off the road if pollution gets extremely bad, but this hasn't been ordered yet, the Associated Press reports.

"Yesterday, I thought it was bad enough when I went out to eat. But this morning I was hacking,"  Beijing pedestrian  Li told AP.

Despite how bad it may be, the government has not issues a red alert. To reach the highest level, there must be a forecast of severe pollution for three days in a row. Pollution that is expected to clear in less than three days don't trigger high alerts and stringent measures. If the highest alert was issued, 5 million cars would have to be taken off the road, based on the last digit on their license plate.

In January, density readings were recorded at PM(particulate matter) 2.5 particles exceeding 500 microgram per cubic meter. This only triggered a blue alert, which is the lowest. The density is about 20 times as high at the 25 micrograms which is considered safe by the World Health Organization. Particulate matter is a mix of extremely small particles and liquid droplets which can cause health problems.

During this orange alert, members of the public are asked to use public transportation and not to let their cars run idle. The streets are also being sprinkled with water and dust-control measures are in effect at building sites.