Toxic haze blanketed Kathmandu valley this afternoon, leaving those out in the open with burning eye sensation and breathing difficulty.

Rishiram Sharma, former government secretary and chief of the Department of Hydrology and Meteorology, told THT that sudden change in atmospheric carbon dioxide concentration in the afternoon was an unusual phenomenon. "Kathmandu valley has developed a winter inversion layer which traps pollution inside the city. Low wind speeds prevented the dispersion of pollutants and inversion layer led to trapping of pollutants," he said.

Photo: Skanda Gautam/THT
Photo: Skanda Gautam/THT

Sharma attributed the yellowish smog to the poor local wind speed within the city and wildfires raging in forests near the valley, mainly in Makawanpur.

He said smoke emitted by brick kilns, vehicular emission, open burning of refuse, and dust from construction sites had contributed to the increased level of hazardous haze in the valley.

According to the Ministry of Home Affairs, more than 110 places in the country have reported forest fires in the past one week. Langtang National Park, which is 32 kilometres north of the capital, also witnessed a massive wildfire today. The valley is bowl-shaped basin, which usually does not permit air to flow out, trapping pollutants during the winter.

Khem Raj Bhusal, a physician, warned that high concentration of pollutants in the air could cause skin and eye allergies.

"Burning and irritation in the eyes are quite common during dry season. We should avoid toxic outdoor air and wear protective mask even indoors. This smog can cause respiratory tract infection," he said.

Bhusal said COVID patients in recovery stage and those with pre-existing heart and lung diseases are more vulnerable to smog, which comprises harmful chemicals such as nitrogen oxides, sulphur dioxide, and carbon monoxide.

The Air Quality Index reached 294 in Kathmandu today at 5:00pm. Statistics by the Department of Environment indicated an AQI of 443 in Bhaisepati, 221 in Kirtipur, and 220 in Bhaktapur this afternoon. DoE Spokesperson Indu Bikram Joshi said wildfire and internal pollution load had resulted in smog.

According to international standards, an AQI value below 50 means good air quality, while AQI above 300 is hazardous.

The air quality and pollution city ranking updated by IQAir, a Switzerland-based air quality technology, ranked Kathmandu the most polluted city with 275 AQI, followed by Beijing (186 AQI) and Mumbai (169 AQI).

On January 4, the Air Quality Monitor placed at the US Embassy, Phora Durbar in Kathmandu, had recorded 500 AQI, an unprecedented level of air pollution.

Smog affects flights

Poor visibility due to smog affected international and domestic flights at Tribhuvan International Airport for over two hours today.

According to the TIA Office, Cathay Pacific aircraft arriving in Kathmandu via Hong Kong was diverted to India, while Nepal Airlines flight from Delhi, Air India flight from Delhi, and Himalaya Airlines flight from Dammam, Saudi Arabia, could land at TIA after being held in the air for almost an hour.

In the domestic sector, Yeti Airlines' flight from Pokhara to Kathmandu was diverted to Janakpur; Buddha Air's aircraft from Pokhara, Janakpur, and Rajbiraj were also diverted to Janakpur; Buddha's aircraft from Nepalgunj was diverted to Bhairahawa; A Saurya Airlines' flight from Chandragadi had to return to Chandragadi; and Shree Airlines' flight from Dhangadi was diverted to Bhairahawa. However, all the diverted flights landed at TIA after 5:00pm.

Six flights, three each of Buddha Air and Yeti Airlines, from Pokhara to Kathmandu were cancelled today. Visibility of 800 metres is considered fair for international flights taking off from TIA, but those landing at TIA require a visibility of more than 1,600 metres. The lowest visibility at TIA today was below 800 metres. It gradually improved after 5:00pm.

A version of this article appears in the print on March 27, 2021, of The Himalayan Times.