Skopje landed in the top spot of most polluted cities in the world after its air quality index reached a high of 430 on Saturday, Jan. 19, at 1 am, according to AirVisual.

The Switzerland-based organization that has gathered the largest global database of air quality data by city since 2015 uses a six-marker scale of danger concerning the levels of air pollution, from “healthy” to “hazardous.”

The AirVisual index ranges from 0-500, and any city reaching levels higher than 300 is considered hazardous.

Due to the enormous levels of air pollution, the City of Skopje issued a health advisory Friday urging citizens to avoid spending time outdoors; to use public transport or carpool; to refrain from burning waste oil and other toxic substances, as well as to keep chimneys clean of ash and soot.