New Delhi India air pollution smog airport
Credit: SAJJAD HUSSAIN/AFP/Getty Images

United Airlines resumed service to New Delhi on Monday after canceling two days of flights due to the city’s smog levels.

The airline said in a statement that the cancelations were because “advisories as the region remains under a public health emergency.” They compared the air quality to that after a natural disaster, such as a hurricane or volcano explosion. Smog has the potential to obscure pilots’ visibility during landing.

On Sunday, the air pollutant PM 2.5 levels in New Delhi were at 721. The World Health Organization categorizes anything above 300 as “hazardous.” The pollutant is 30 times finer than human hair and can lodge itself into lungs when inhaled.

Although Delhi’s air quality is consistently among the worst in the world, smog in the city has increased dramatically over the past few weeks, due in part to falling temperatures. Last week, New Delhi’s Chief Minister likened the city to a “gas chamber” because of its smog. More than 6,000 schools were closed and incoming trucks have been banned from the city until smog levels drop. The government urged citizens to stay inside and wear masks if they go outside.

United is the only airline that canceled flights to the city. Passengers affected by the cancelation receive a travel waiver to rebook their flights at no additional cost.

A spokesperson for the airline said that they will “continue to monitor conditions over the next few days.” Passengers traveling to New Delhi can visit their airline’s website for any updates regarding travel.