Air quality in the Kathmandu Valley worsened on Monday reaching unhealthy levels and raising serious public health concerns.

Although decline in air quality during winter and dry seasons is a common phenomenon, a sudden rise in air pollution levels is alarming, public health experts say.

“The number of patients with serious respiratory illnesses has already risen in our hospital,” said Dr Ravi Shakya, director at the Patan Hospital. “The worsening air quality will further exacerbate the problems.”

According to IQ AirVisual, a Swiss group that collects air-quality data from around the world, Kathmandu ranked seventh most-polluted city in the world with PM2.5 levels reaching 154 micrograms per cubic metre (μg/m3) on Monday morning. Butwal recorded 158 micrograms per cubic metre (μg/m3) and Meghauli of Chitwan recorded 157 micrograms per cubic metre (μg/m3) in the afternoon.

PM2.5 refers to particulate matter (solid or liquid droplets) in the air that is less than 2.5 micrometres in diameter. It is among the most dangerous pollutants that can get past the nose and throat to penetrate the lungs and even the bloodstream. PM2.5 particles are small and are also likely to stay suspended in the air for long, increasing the chances of people inhaling them.

As per the Environmental Protection Agency’s air quality index, when air quality reaches 151–200, it is considered unhealthy; everyone may experience problems, with sensitive groups feeling more severe effects.

Meanwhile, New Delhi, the capital city of India, has been witnessing a ‘severe plus’ category pollution in recent days prompting authorities concerned to enforce measures including shutting down schools, enforcing ban on polluting trucks, commercial four-wheelers and all types of construction, according to media reports.

“Until a few days ago, we had clear skies, but now it’s mostly overcast, and the air quality has reached unhealthy levels,” said Bhusan Tuladhar, an environmentalist. “Quality of air will reach hazardous levels in the coming days, as burning of agricultural residue has started in the Tarai and polluted air is coming from India.”

Experts cited the growing use of combine harvesters by farmers in the Tarai region and apathy of agencies concerned to prevent open burning as among the reasons for the rise in air pollution. Open burning of agricultural residue, which is among the chief culprits for the rise in the level of air pollution, has begun with the start of the harvesting season.

According to a report titled ‘A model-ready emission inventory for crop residue open burning in the context of Nepal’, trends in dry matter generation have increased from 2003/04 to 2016/17 and so have the trend of emissions in the country.

Along with the burning of agricultural residue, incidents of forest fire and several other factors—emissions from brick kilns, factories, vehicular movements and construction activities, among others—will contribute to the deterioration of the air quality of the country.

Experts say the deterioration of air quality seriously affects public health. According to doctors, poor air quality causes both short- and long-term effects on public health. Bad air quality can cause pneumonia, bronchitis, conjunctivitis, skin allergy, stroke and heart problems, among others, in the short term, and ulcers and cancer of the lungs and intestine, kidney disease and heart problems in the long run.

Experts blamed the apathy of the authorities in enforcing measures to improve air quality for worsening pollution levels. The people are bearing the brunt of the authorities’ indifference, they said.

Studies show that polluted air has been shortening the lives of Nepali people. Polluted air has been cutting short the lives of Nepali people by around five years, according to a new report by the Air Quality Life Index (AQLI) that converts air pollution concentration into impact on life expectancy. AQLI is a metric produced by the Energy Policy Institute at the University of Chicago.

Toxic air is deadlier than tobacco use and high blood pressure, which reduce life by 2.8 years and 1.7 years, respectively.

The reduction in life expectancy depends on where one lives—7.5 years in Mahottari, 7.4 years in Rautahat and Dhanusha, and 7.2 years in Sarlahi and Bara districts, the AQLI report said. Likewise, the pollution has been shaving 6.7 years off the lives of people residing in Siraha, and 6.2 years in Saptari and Rupandehi districts.

These districts lie in southern Nepal and share borders with the highly-polluted northern plains of India.

“Some areas of Nepal fare much worse than average, with air pollution shortening lives by 6.8 years in the nine districts with the highest concentration of particulate pollution,” reads the report. “If Nepal were to reduce particulate pollution to meet the WHO guideline, residents in the mid and eastern Terai region—where nearly 40 percent of Nepal’s population resides—would gain 6.5 years of life expectancy. In the capital city of Kathmandu—Nepal’s most populous city—residents would gain 3.5 years of life expectancy.”

According to Bhupendra Das, an air quality expert, launching awareness drives against the hazards of open burning, making waste management effective, prohibiting burning of waste in the open, and restricting unnecessary vehicular movement can help improve air quality. “All agencies concerned, especially local bodies, should shoulder the responsibility to lessen emissions, especially those from open burnings,” he said.