Air Quality and Travel: Protecting Your Health in Polluted Cities

Air quality apps show you a colour. They rarely tell you the number that predicts whether you will end up in a hospital. Here's what to do with that data before and during your trip.

Air quality and travel: the number most travellers ignore

The 2024 World Air Quality Report found that 91% of 138 countries exceeded the WHO annual PM2.5 guideline of 5 µg/m³. That is not a statistic about residents. It is a statistic about the air you will breathe the moment you land.^[1]

This article covers what the Air Quality Index (AQI) numbers actually mean for your body, which cities and seasons carry the highest risk, and the specific steps you can take before and during a trip to reduce your exposure.

Medical disclaimer: This article is for informational purposes only and does not constitute medical advice. If you have a respiratory, cardiovascular, or other pre-existing condition, consult your specialist before travelling to high-pollution destinations. Regulations and air quality conditions change; verify current data before you travel.

What the AQI colours are not telling you

Most travel apps present AQI as a colour band: green, yellow, orange, red. The number underneath that colour is what you actually need. On the US EPA scale, which underpins the AQI readings shown on tools like IQAir and WAQI, an AQI above 100 is considered unhealthy for sensitive groups, and above 150 it is unhealthy for everyone.^[2]

The primary concern is PM2.5, fine particles smaller than 2.5 micrometres. PM2.5 can penetrate deep into the lungs, enter the bloodstream, and travel to organs, causing systemic damage. A surgical mask or cloth face covering does not filter particles at this size.^[3]

The colour on your app is calibrated for a general population average. If you have asthma, COPD, hypertension, or a cardiovascular condition, your threshold for adverse effects sits lower than that average. You need to read the raw number, not the colour.

Which destinations carry the highest risk, and when

The State of Global Air 2024 report identified air pollution as the second largest risk factor for death globally, with South Asia and sub-Saharan Africa carrying the highest burden. For travellers, the practical concern maps to specific cities and seasons.^[4]

Delhi, India, consistently records annual average PM2.5 concentrations that exceed the WHO guideline by a factor of more than ten, with the worst readings occurring October through January when agricultural burning and cold weather trap pollution at ground level. Lahore, Pakistan, faces a similar seasonal pattern.

In Bangkok, Thailand, the February to April period brings PM2.5 spikes driven by crop burning in the north, pushing readings regularly above AQI 150 in the city centre.

Jakarta, Indonesia, and Hanoi, Vietnam, have chronic year-round particulate pollution from traffic and industry, with peaks in the dry season. Mexico City, Mexico, sees ozone and PM2.5 spikes in spring when thermal inversions trap vehicle emissions in the valley basin. None of these places are off-limits. They do require a specific preparation plan.

The health effects that catch travellers off guard

Acute exposure to high PM2.5 can trigger symptoms within hours. Short-term effects include difficulty breathing, chest pain, wheezing, and eye, nose, and throat irritation. For travellers without any diagnosed condition, these can feel like a heavy cold or an unexpected allergy flare.^[5]

The cardiovascular risk is less obvious but well-documented. PM2.5 is linked to ischemic heart disease, ventricular arrhythmia, and risk of pulmonary embolism. Research published in peer-reviewed literature noted that myocardial infarctions and cerebrovascular accidents are among the most common causes of death in international travellers, and a plausible link to acute pollution exposure exists for susceptible individuals.^[6]

Ground-level ozone, the other major urban pollutant, adds a separate layer of risk. Ozone concentrations rise on hot, sunny, still days. It increases the frequency of asthma attacks and can cause permanent lung damage through repeated exposure.

Before you fly: the preparation steps that actually matter

Check the seasonal AQI baseline, not just the forecast. Real-time AQI apps show today's reading. What you need before booking is the historical monthly average for your destination. IQAir and the World Air Quality Index project (WAQI) both publish historical data by city. Check the average AQI for the month you plan to travel, not just the day you searched.

Talk to your prescribing doctor if you have a respiratory or cardiovascular condition. If you use a preventer inhaler, carry a reliever and confirm your action plan covers a pollution flare, not only allergen triggers. If you take antihypertensive medication, ask whether your current regimen is sufficient given the additional cardiovascular stress of high-pollution exposure.

Pack a properly rated mask. Cloth masks and standard surgical masks do not filter PM2.5 particles effectively. N95, KN95, and FFP2 masks are the minimum standard for particulate filtering. Buy them before you travel; availability and quality at destination vary considerably.

Peer-reviewed modelling published in GeoHealth found that N95 respirators reduce PM2.5 exposure by more than a factor of 14 when worn with a proper seal, compared with no mask. Surgical masks reduced exposure by a factor of only 1.7.^[7]

Store your medical summary somewhere accessible. An emergency physician in Delhi or Jakarta needs to know your current medications and relevant history immediately, without a language barrier. The Nomedic app lets you carry your IPS (International Patient Summary) on your phone, structured to the HL7 FHIR standard that clinical systems internationally can read.

On the ground: adapting your behaviour to local air quality

Open the AQI app each morning before you plan outdoor time. On days when the reading is above 100, move strenuous activity indoors. Running, cycling, and sightseeing on foot all increase respiratory rate, which means you inhale more polluted air per hour.

The US EPA and Johns Hopkins Medicine both recommend keeping windows closed and using air conditioning on recirculate mode when outdoor air is heavily polluted. In a hotel room, shut the windows overnight rather than relying on natural ventilation, particularly in cities like Delhi, Lahore, and Jakarta where pre-dawn AQI readings are often the worst of the day.^[8]

Avoid high-traffic streets for outdoor walking, particularly during peak vehicle hours. Side streets and parks in most cities have measurably lower local pollutant concentrations than main roads, even if the city-wide AQI is identical.

If you have a pre-existing condition: the higher-risk scenarios

People with asthma or COPD, older adults, children, and those with hypertension or heart disease face compounded cardiovascular and respiratory risks from poor air quality. For these groups, an AQI above 100 in the destination city should trigger an explicit pre-travel consultation, not just a general review.^[9]

Pregnancy adds further consideration. WHO evidence links maternal PM2.5 exposure to preterm birth and low birth weight. If you are pregnant and planning extended time in a high-pollution city during winter or agricultural-burning season, discuss the specific timing and exposure risk with your obstetrician.

For travellers managing asthma specifically, city-level preparation matters beyond the mask. Indonesia's wildfire haze, which affects Bali and Jakarta from July to October, is one of the most acute seasonal pollution events in the Asia-Pacific region. See the dedicated guide on asthma in Indonesia for inhaler import rules and pharmacy access specific to that context.

The tools worth using

The World Air Quality Index project (waqi.info) provides real-time AQI readings from over 10,000 monitoring stations in 80 countries. IQAir adds historical city-level data and a 7-day forecast. Both are free. Use the station nearest your accommodation, not the citywide average, since readings within a single city can vary by 50 AQI points depending on proximity to traffic or industrial zones.^[10]

The WHO also maintains an air quality standards database updated in 2025 that compiles national PM2.5 and PM10 standards from approximately 140 countries. Cross-referencing a destination country's national standard against the WHO guideline of 5 µg/m³ tells you how seriously that government takes air quality regulation.^[11]

If your medication requires specific storage or carries a complex dosing schedule that an emergency clinician would need to understand quickly, store a summary in your Nomedic IPS before you travel. Temperature extremes compound pollution stress for travellers managing chronic conditions, and a well-maintained medical record is the single most useful document you can hand to a doctor in a foreign emergency department. See also the glossary entry on cold-chain medication if your treatment requires refrigeration.

A practical checklist before you land

Check the historical monthly AQI for your destination city before booking. If the average exceeds 100 for your travel month, build mitigation steps into your itinerary. If the average exceeds 150, discuss the trip with your doctor before confirming.

Pack at least four N95, KN95, or FFP2 masks per week of travel. One mask is good for roughly 8 hours of use before filtration efficiency drops. Reusing a damp mask provides less protection than a fresh one.

Book accommodation that offers air conditioning with a recirculate setting. If you are staying in a building without mechanical ventilation, a portable air purifier with a HEPA filter is worth carrying for stays of more than three nights in a high-pollution city.

Know the local emergency number before you arrive. In India it is 112. In Indonesia it is 119. In Thailand it is 1669 for medical emergencies. In Mexico it is 911. Do not rely on finding this information at the moment you need it.

Frequently asked questions

How do I check air quality before and during a trip abroad?

IQAir and the World Air Quality Index project (waqi.info) both offer free real-time and historical AQI data for thousands of cities. Before booking, check the monthly average AQI for your destination during your planned travel month. During your trip, use the station nearest your accommodation rather than the citywide average, as readings vary significantly by neighbourhood.

What is the difference between AQI and PM2.5 readings?

PM2.5 is a direct concentration measurement in micrograms per cubic metre. The AQI is a standardised index that converts multiple pollutant readings (PM2.5, PM10, ozone, NO2, SO2, CO) into a single number on a 0-500 scale. The WHO annual guideline for PM2.5 is 5 µg/m³; a PM2.5 concentration of around 12 µg/m³ corresponds to an AQI of approximately 50 on the US EPA scale.

Does an N95 mask actually protect against city air pollution?

Yes, when worn with a proper seal. Peer-reviewed research published in GeoHealth found N95 respirators reduce PM2.5 exposure by more than a factor of 14 compared with no mask. Surgical masks and cloth coverings reduced exposure by a factor of 1.7 and 1.9 respectively, which is not sufficient protection in high-pollution conditions. The seal around your nose and jaw is the critical factor.

Can air pollution trigger a heart attack while travelling?

Research links acute PM2.5 exposure to increased risk of cardiac arrhythmia, ischemic heart disease, and pulmonary embolism. Studies also note that myocardial infarctions and strokes are among the most common causes of death in international travellers. If you have a pre-existing cardiovascular condition, check the AQI forecast daily and avoid heavy outdoor exertion on high-pollution days.

Which months have the worst air quality in Bangkok?

Bangkok's worst air quality typically runs from February to April. Agricultural burning in northern Thailand during the dry season pushes PM2.5 readings in the capital above AQI 150 on multiple days. The city's own traffic and construction pollution adds to this seasonal baseline.

Is it safe to travel to Delhi in winter if I have asthma?

Delhi's PM2.5 levels October through January regularly exceed AQI 300, which is classified as hazardous on the US EPA scale. If you have asthma, consult your respiratory specialist before booking a winter visit, confirm your rescue inhaler supply, and plan to spend most time indoors with filtered air. Avoid early morning and late evening outdoor exposure, when pollution is typically at its worst.