How to protect yourself from air pollution in Nepal

The pollutant that does most of the health damage is PM2.5 — particulate matter smaller than 2.5 micrometres. Particles that small are not filtered out by the nose and upper airway. They reach deep into the lungs, and the smallest cross into the bloodstream, which is why air pollution is associated with cardiovascular disease and stroke as well as with respiratory illness.

In the Kathmandu valley the sources are mixed: vehicle exhaust, brick kilns operating in the dry season, road and construction dust, open waste burning, and residential burning for cooking and heating. Regional transport matters too — research across the Hindu Kush Himalaya has established that pollution moves between countries and that haze in the region is not purely local in origin.

The seasonal pattern is the thing to internalise. During the monsoon, rain scavenges particles out of the air and the atmosphere mixes vertically, and Kathmandu's air is often genuinely good. Through the dry winter the inversion sets in, and concentrations climb. People frequently associate bad air with the visibly hazy pre-monsoon months, but the sustained high-concentration periods are typically the cold, still ones.

Within a day the pattern repeats in miniature. The inversion is strongest when the ground is coldest, so early morning and the hours after sunset are the worst. Midday and early afternoon, when the sun has warmed the surface enough to break the inversion and allow mixing, are usually the cleanest hours.

This gives you a genuinely useful piece of scheduling advice that costs nothing: move outdoor exercise from dawn to late morning. In Nepal, where a morning walk is close to a national habit, this is the single behavioural change with the largest effect for the least effort.

Spring adds a different problem: forest fire and agricultural burning smoke, which in bad years produces sustained regional haze across the country rather than just in the valley. That smoke is chemically different and its effects are the same.

An air quality index converts pollutant concentrations into a single number with colour bands, and it is the practical tool for deciding what to do on a given day. Nepal's Department of Environment operates the national air quality monitoring network and publishes air quality status reports and statistics.

Use it as a decision rule rather than as a source of anxiety. The useful questions are: should I exercise outdoors today, should the children play outside, should I close the windows, and should I wear a respirator on the commute. A number that never changes your behaviour is not being used.

Be aware that different countries use different index scales, so the same concentration can produce a different index number and colour depending on whose index an app is showing. If you compare two apps and get two answers, that is usually why. What matters is the underlying concentration and the direction it is moving.

Location matters more than people expect. A monitoring station on a green campus and a roadside near a busy junction can differ substantially at the same moment, and your personal exposure is dominated by where you actually spend time — which for most people means a commute on a main road.

Check the trend, not just the instant value. Because of the inversion, a reading at 7am tells you very little about 1pm. Looking at the shape of the day lets you place outdoor activity in the cleaner window rather than avoiding the outdoors altogether, which is neither necessary nor good for you.

And keep perspective on relative risk. Physical activity is strongly protective for health, and the answer to polluted air is almost never to stop exercising. It is to move the exercise indoors or to a cleaner hour on the worst days.

Start with cooking. Where solid fuel — wood, dung, crop residue, coal — is burned indoors on an open fire or a poor stove, concentrations in the kitchen dwarf anything outdoors. The World Health Organization identifies household air pollution from solid fuel cooking as a leading environmental cause of illness and premature death, and it falls disproportionately on women and young children who are in the kitchen.

The fixes, in order of effectiveness: switch to LPG, electricity or a genuinely improved cookstove; vent the smoke outside through a chimney or hood; and keep small children out of the kitchen while cooking. Simply opening a window is better than nothing and much worse than a chimney.

Then look at the bedroom. You spend a third of your life there, and a bedroom window facing a busy road, left open overnight, is drawing in the most polluted air of the day during exactly the hours you are breathing steadily in it. Closing it during the morning and evening peaks and opening it in the early afternoon reverses that.

If you buy one air purifier, put it in the bedroom rather than the sitting room, and make sure it is rated for the room's size. A HEPA filter in a closed bedroom is the highest-value air quality purchase available to a household, and a purifier in a large open living area with doors open is close to decorative.

Do not burn things indoors for warmth without ventilation. Charcoal and coal heaters in a sealed room produce carbon monoxide as well as particulates, and carbon monoxide kills people in Nepal every winter. If you use one, ventilate, and never sleep with it burning in a closed room.

Reduce indoor dust, which carries the same particles. Damp-mop rather than dry-sweep, keep doormats, and take outdoor shoes off at the door.

Finally, deal with tobacco smoke as what it is: the largest single indoor air pollution source in any home where someone smokes indoors, and the one entirely within a household's control.

A mask helps only if it seals. PM2.5 particles do not need a gap to get through — they follow the path of least resistance, and an unsealed edge is exactly that. A cloth mask or a loose surgical mask provides very little protection against fine particulates, whatever it does for droplets.

What works is a properly fitted respirator — an N95, KN95, FFP2 or equivalent — worn with the nose clip moulded to your face and both straps used as designed. If air leaks around the edge when you breathe in, it is not doing the job. Facial hair breaks the seal.

The commute is where a mask earns its cost. Time spent on a motorcycle or in traffic on a main road is short in hours and disproportionate in exposure, because you are directly in the exhaust plume. This is also the exposure most people accept without thinking about it.

Where you can, change the route rather than only the equipment. A back street parallel to a main road can be dramatically cleaner, and a few minutes longer. Riding at the front of a queue at a junction rather than behind a bus makes a real difference for a small behavioural change.

Vehicle cabin filters work if the ventilation is set to recirculate rather than to draw outside air. A car with the vents on fresh air in traffic is a box of exhaust.

For outdoor workers — traffic police, street vendors, construction and brick workers, drivers — exposure is occupational and continuous, and this is where the individual measures are least adequate. A well-fitted respirator, provided and replaced by an employer, is the minimum, and it is a workplace responsibility rather than a personal choice.

Do not stop exercising. Move it indoors on the worst days, shift it to the cleaner middle of the day, and take it away from main roads. The health benefit of regular physical activity is large and well established, and abandoning it is a worse trade than the pollution exposure it avoids.

Children are more exposed than adults because they breathe faster relative to body size, their lungs are still developing, and they are lower to the ground where road dust concentrates. Effects on lung development in childhood are not fully reversible, which is why school and home measures matter more than they might appear to.

Older people, people with asthma or chronic obstructive pulmonary disease, people with heart disease, and pregnant women are the other high-risk groups. For someone with asthma or COPD, a high-pollution period is a foreseeable trigger, and the sensible response is to make sure medication is current and inhalers are to hand before the winter rather than during an exacerbation.

Know the symptoms that warrant medical attention rather than waiting them out: breathlessness at rest, wheeze that does not respond to a reliever inhaler, chest tightness or pain, a cough producing blood, or confusion. Chest pain and severe breathlessness are emergencies.

Persistent symptoms that are easy to dismiss deserve attention too — a cough that lasts for weeks after a polluted period, worsening exercise tolerance, or repeated chest infections in a child. These are the presentations that get attributed to a lingering cold and are worth a consultation.

Telemedicine has expanded in Nepal and is a reasonable first step for a non-emergency respiratory question, particularly for people outside cities. It is not the route for severe breathlessness or chest pain, which need an emergency department.

Finally, be careful about health information on this subject. Air pollution attracts a large volume of misinformation and a large market in devices, supplements and remedies that do nothing. The interventions with real evidence behind them are dull: cleaner cooking, ventilation, a properly fitted respirator, a HEPA filter in the room you sleep in, and not smoking.