Air Pollution & Health in Nepal: AQI, PM2.5 Levels & Disease Links

The Air Quality Index (AQI) is a 0-to-500+ scale that translates measured pollutant concentrations into a single, colour-coded number so the public can gauge daily health risk at a glance. Most apps used in Nepal, including IQAir and AirNow, report the United States Environmental Protection Agency (US EPA) version of the AQI. Under that scale, 0-50 is 'Good' (green), 51-100 'Moderate' (yellow), 101-150 'Unhealthy for Sensitive Groups' (orange), 151-200 'Unhealthy' (red), 201-300 'Very Unhealthy' (purple) and 301 and above 'Hazardous' (maroon).

The AQI is usually driven by PM2.5, or fine particulate matter smaller than 2.5 micrometres in diameter, roughly one-thirtieth the width of a human hair. Because these particles are so small, they bypass the nose and throat, lodge deep in the lungs and can pass into the bloodstream. PM2.5 is measured in micrograms per cubic metre (ug/m3, sometimes written as micrograms per cubic metre), and it is the pollutant most strongly linked to death and disease worldwide.

AQI and raw PM2.5 are not the same number and should not be confused. A concentration of 45 ug/m3, close to Kathmandu's yearly average, converts to an AQI of roughly 124 ('Unhealthy for Sensitive Groups') under the US scale. The AQI is deliberately non-linear, so a small rise in raw PM2.5 at high pollution levels produces a large jump in the index. When reading a figure, always check whether it is a raw concentration in ug/m3 or an AQI value.

In 2021 the World Health Organization tightened its global air quality guidelines, halving the recommended annual PM2.5 limit from 10 to just 5 ug/m3 and setting the 24-hour limit at 15 ug/m3. These values reflect a review of more than 500 studies showing that health harm continues even at very low pollutant levels. They are health-based targets rather than legally binding limits, but they define the benchmark against which countries measure progress.

Nepal sits far above that benchmark. In IQAir's 2024 World Air Quality Report, Nepal recorded a national population-weighted average PM2.5 of about 42.8 ug/m3, making it the seventh most polluted country in the world and exceeding the WHO annual guideline by more than eight times. Kathmandu's own 2024 average was about 45.1 ug/m3, roughly nine times the WHO limit. In five months of 2024, January, February, March, April and December, the capital's monthly PM2.5 breached the safe limit by more than ten times, with April the worst at around 86.9 ug/m3.

Nepal's own legal standard is also far looser than the WHO guideline. The National Ambient Air Quality Standards, promulgated in 2012 (2069 Bikram Sambat), set the 24-hour PM2.5 limit at 40 ug/m3, eight times the WHO 24-hour figure of 15. Even this weak domestic standard is routinely breached in winter: studies in urban Kathmandu found outdoor PM2.5 above 40 ug/m3 for roughly 90 percent of winter measurements. The gap between what Nepalis breathe and what is considered safe is therefore very large and widest in the cold, dry months.

The Kathmandu Valley is a bowl ringed by hills rising to roughly 2,000 to 2,800 metres, which physically traps pollutants and limits how fast dirty air can disperse. When emissions build up inside this natural basin, they have nowhere to go, so concentrations climb quickly. This geography is the single biggest reason a mid-sized city like Kathmandu ranks alongside far larger megacities on global pollution charts.

The dominant local sources are vehicle exhaust, brick kilns, road and construction dust, and the open burning of waste and biomass. Rapid growth in private vehicles, many of them old and poorly maintained, releases PM2.5, carbon monoxide and nitrogen oxides. Hundreds of brick kilns operate around the valley during the dry season, burning coal and wood, while unpaved roadsides and building sites raise clouds of dust. Household cooking and heating with solid fuels adds further indoor and outdoor particulate load.

Winter makes everything worse through temperature inversion. On cold, still nights a layer of warm air sits above cooler air near the ground, acting like a lid that pins smoke and dust close to where people breathe. With little wind and no monsoon rain to wash the air, pollution accumulates day after day. This is why 'kathmandu air quality' searches spike from roughly November to April, and why forest and agricultural fires in the pre-monsoon spring can push AQI readings into the hazardous range.

Long-term exposure to PM2.5 is causally linked to a specific set of diseases, and Nepal carries a heavy share of each. The World Bank's 2025 report 'Towards Clean Air in Nepal' attributed to air pollution an estimated 75 percent of chronic obstructive pulmonary disease (COPD) cases, 46 percent of strokes, 44 percent of ischaemic heart disease (IHD), 41 percent of lower respiratory infections and 38 percent of lung cancer. Air pollution also contributed to about 30 percent of adverse neonatal outcomes such as low birth weight and preterm birth, and roughly 20 percent of diabetes.

The pathways are well understood. Fine particles inflame and scar the airways, driving COPD and worsening asthma attacks; they enter the bloodstream and promote the clots and plaque behind heart attacks and strokes; and their chemical load, including known carcinogens, raises lung cancer risk. In young children, PM2.5 impairs developing lungs and increases the frequency and severity of pneumonia, still a major killer of Nepali under-fives.

The mortality toll is large. Air pollution is repeatedly identified as a top cause of death and disability in Nepal, with the World Bank citing on the order of 26,000 premature deaths a year and an estimated loss of about 3.4 years of life expectancy for the average Nepali. Chronic respiratory disease alone accounted for roughly 16 percent of all deaths in 2019, up sharply from earlier decades. By share of pollution-attributable deaths, ischaemic heart disease, stroke, COPD, lung cancer and lower respiratory infections consistently top the list.

Air pollution harms everyone, but some groups face sharply higher risk from the same exposure. Children breathe faster relative to body size, spend more time active outdoors, and have lungs that are still developing, so PM2.5 can cause lasting damage and frequent respiratory infection. Older adults and anyone with existing heart or lung conditions, including COPD, asthma, angina or previous stroke, are more likely to be hospitalised or die when pollution spikes.

Pregnant women are another priority group, because maternal PM2.5 exposure is linked to low birth weight, preterm delivery and other neonatal complications. Outdoor workers, traffic police, street vendors, construction labourers and drivers accumulate very high daily doses simply through their jobs. Households that still cook or heat with wood, dung or coal add indoor particulate exposure on top of the ambient outdoor load, a burden that falls disproportionately on women and young children at home.

Because these vulnerable groups react at lower AQI levels, the 'Unhealthy for Sensitive Groups' (orange, AQI 101-150) category is the practical trigger for caution in Nepal. On many winter days Kathmandu sits in or above this band, meaning at-risk residents should be adjusting their behaviour for weeks at a stretch, not just on the worst days.

Individuals cannot fix Nepal's air on their own, but sensible habits meaningfully cut personal exposure. The single most useful tool is a real-time AQI reading from a trusted source such as IQAir, the Department of Environment's monitoring portal, or a local sensor, checked before planning outdoor activity. When the AQI is orange or worse, reduce strenuous exercise outside, keep windows closed at peak pollution hours, and reschedule children's outdoor play.

On high-pollution days a well-fitted respirator mask rated N95 or FFP2 filters most fine particles, whereas cloth or surgical masks offer little protection against PM2.5. Indoors, a HEPA air purifier sized to the room can substantially lower particle levels, and switching from solid-fuel to clean cooking, along with good kitchen ventilation, reduces the indoor load that often exceeds outdoor levels in traditional homes. People with asthma or heart disease should keep medication on hand and follow their doctor's action plan during smog episodes.

These are mitigation measures, not a cure; durable improvement depends on cutting emissions at source through cleaner vehicles and fuel, tighter brick-kiln technology, dust control at construction sites, and an end to open burning. Nepal's official 40 ug/m3 standard is itself far above the WHO guideline, so lasting protection also requires policy and enforcement, not personal precautions alone.