Officials in Beijing have issued the city’s first red alert for smog.

The Chinese capital city’s Municipal Environmental Protection Bureau issued the alert on Monday. In a translated posting on its website, the bureau said the warning was issued “to protect public health” and “reduce the degree of air pollution.”

The posting indicates that “heavy air pollution” is expected to continue through Thursday.

The Associated Press reported that the levels of fine particle matter (called PM 2.5) were approaching 300 micrograms per cubic meter on Monday. That’s 12 times the level that the World Health Organization, an arm of the United Nations, lists as a guideline for those particles.

The website posting indicates that schools are encouraged to close and that officials will be strengthening emergency measures. The city is also stepping up its public transportation and instituting alternating driving days for vehicles, among other pollution-curbing techniques.

The Xinhua News Agency reported it’s the only time a red alert was issued in Beijing since 2013, the year in which the city implemented emergency management protocols for air pollution.

The red alert was issued as leaders from China and nearly 200 other countries were entering the second week of a two-week climate changes summit in Paris. Much of the focus at the COP21 conference is how to reduce global greenhouse gas emissions and curb rising temperatures.

China emits more greenhouse gasses than any other country in the world.