Air quality in most parts of the country, including the Kathmandu Valley, which had been at its worst until a month ago, had improved with the intensification of premonsoon activities—rainfall and windstorms.

However, with the pause in premonsoon conditions in recent days, combined with rising temperatures and forest fire incidents, air quality began to worsen again.

On Wednesday morning, air quality in most parts of the capital city had reached a very unhealthy level with PM2.5 levels either exceeding 200 or close to 200 micrograms per cubic metre.

What concerns experts much is that another round of rainfall and strong winds is needed to improve air quality, as little substantive action has been taken by the authorities to address the rising air pollution, which is affecting the health of most people across the country.

“Even the 100-point roadmap of the incumbent government did not include a plan to address rising air pollution levels,” complained Bhusan Tuladhar, an environmentalist. “But we are still hopeful that the majority government formed after the election will take initiatives to address the problems of air pollution, from which everyone in the country has been affected.”

PM2.5 refers to particulate matter (solid or liquid droplets) in the air less than 2.5 micrometres in diameter. These are 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 tend to remain suspended in the air for extended periods, increasing the risk of inhalation.

According to IQAir, a Swiss group that collects air-quality data from around the world, PM2.5 levels at the Changunarayan area in Bhaktapur reached 223 micrograms per cubic metre and at Madhyapur 204. PM 2.5 levels in most places in the Valley were close to 200micrograms per cubic metre.

Experts blamed rising forest fire incidents and the ongoing agricultural residue burning for worsening air quality.

“This is the peak forest fire season, and deterioration in air quality is expected at this time,” said Tuladhar. “Premonsoon activities, including rainfall, started after mid-March have given us much relief.”

There were 51 separate incidents of forest fire on Tuesday. Experts say the last week of April is peak forest fire season during which the majority of the forest gets burned. Likewise, farmers in the Tarai region are in a rush to harvest wheat crops and clear land to prepare for other crops.

“These days farmers use combine harvesters, especially in the Tarai region, which cut the crops mid-stalk, leaving behind residues that farmers later burn,” said Bhupendra Das, an air quality expert. “Farmers also burn weeds, vegetation and dry leaves to prepare land for new cultivation. The rise in labour migration and increase in labour costs have further encouraged farmers to use machines, which in turn is fuelling open burning.”

Moreover, the peak forest season has started. Experts say the trend of the past decade shows that peak forest fire incidents occurred in the last week of April, during which most forests are burned. The wildfire incidents then decline slowly.

Forest fire experts say that the number of forest fire incidents could go up until mid-May this year, as compared to previous years.

“Preparedness and mitigation plans to reduce forest fire incidents have been formulated and are currently being implemented,” said Sundar Sharma, a forest fire expert. “However, their effectiveness remains to be seen.”

Air pollution has emerged as the number one risk factor for death and disability in Nepal, surpassing malnutrition and tobacco use, according to the 2025 World Bank report.

The report titled, ‘Towards Clean Air in Nepal: Benefits, Pollution Sources, and Solutions,” unveiled on Tuesday, stated that polluted air cuts life expectancy by 3.4 years for the average Nepali and causes approximately 26,000 premature deaths annually.

“Air pollution heavily contributes to various diseases: 75 percent of chronic obstructive pulmonary disease cases, 46 percent of strokes, 44 percent of ischemic heart disease, 41 percent of lower respiratory infections, 38 percent of lung cancer, 30 percent of neonatal issues like low birth weight and preterm birth, and 20 percent of diabetes,” reads the report.

Economically, the consequences are severe. “It affects labor productivity due to increased health-related absences and impaired cognition. The negative impact on the tourism industry and the aviation sector is also significant. The economic cost of poor air quality is estimated to exceed six percent of Nepal’s GDP each year,” the report says.

The main sectoral sources of air pollution in the Valley are industrial production, cooking, and mobility, and these will remain dominant over the next decade unless further action is taken, according to the report.

Industrial fuel combustion — led by boiler usage — is expected to increase significantly. Forest fires dominate during the dry months (February to May) and constitute the fourth largest local source of annual average air pollution exposure, the most relevant metric for adverse impacts on public health. Transboundary air pollution significantly impacts air quality in both the Kathmandu Valley and in the Terai region.

These levels would result in tens of thousands of additional premature deaths, particularly impacting children and the elderly, a further strain on the healthcare system, and a growing drag on productivity and competitiveness, warns the report.