A metro train leaves a station amid heavy fog in Lahore, capital of Pakistan's Punjab province on Jan. 19, 2021. Dense fog shrouded several cities in Pakistan on Tuesday. (Photo by Sajjad/Xinhua)

A man cleans a road amid heavy fog in Lahore, capital of Pakistan's Punjab province on Jan. 19, 2021. Dense fog shrouded several cities in Pakistan on Tuesday. (Photo by Sajjad/Xinhua)