United Airlines cancelled two Newark-Delhi Int’l flights after heavy smog had covered the Indian capital.

The temporal suspension has been implemented on November 10 according to the carrier’s announcement. It was originally scheduled to last at least until November 13, but eventually, only flights departing Newark on November 10 and November 11 were cancelled, according to ch-aviation analysis of FlightRadar24 ADS-B data.

The 7,304-mile-long route is one of the longest services in United’s network, lasting 14 hours eastwards and 15:30 hours westwards. The flights were cancelled not due to low visibility in India, but because the airline feared for the health of their crews and passengers.

Air India (AI, Mumbai Int’l), which also operates the Newark-New Delhi route with a stopover in Mumbai Int’l did not cancel any services.

Delhi consistently ranks among the most polluted cities in the world. The concentration of mid-sized pollution particles (PM10) has reached nearly a 1000 micrograms per cubic metre last week, exceeding the World Health Organization’s threshold twenty times over. According to the Air Quality Index website, the levels have currently dropped significantly, but still exceed 700 micrograms per cubic metre.