Environment and daily life — air, sun, water, food, being prepared, and travel

The Air Quality Index (AQI) turns measurements of five common pollutants — ground-level ozone, particle pollution (PM2.5 and PM10), carbon monoxide, sulfur dioxide and nitrogen dioxide — into one number on a scale of 0 to 500, in six colour-coded bands from Good to Hazardous.

Above the WHO guideline limits

Almost the whole world population breathes air above WHO guideline limits. Read the full guide: Air quality index, explained. Check a published reading with the Air Quality Index Lookup. For reading an AQI from another country — the US, China and Vietnam scales side by side — see Reading air quality in another country.

The Global Solar UV Index runs from 0 upward: 0–2 Low, 3–5 Moderate, 6–7 High, 8–10 Very High, 11+ Extreme.

What changes the index

It depends on sun elevation, latitude, cloud cover, altitude, ozone and ground reflection.

The official protection messages

The official WHO protection messages are shade during midday hours, a shirt, sunscreen, a hat and sunglasses. Read the full guide: UV index scale, explained. Check a published index with the UV Index Lookup.

Water, sanitation and hygiene — WASH — are systems: safely managed drinking water, safely managed sanitation, and hygiene services at home.

The gaps, in numbers

The WHO/UNICEF Joint Monitoring Programme is the custodian of the global estimates, and its 2025 report puts the gaps at 2.1 billion people without safely managed drinking water and 3.4 billion without safely managed sanitation.

Handwashing: 20 seconds

Handwashing with soap and water for at least 20 seconds is the CDC’s stated scrubbing time. Read the full guide: What is WASH? Water, sanitation, hygiene. Try the Water, Sanitation and Hygiene Tool.

WHO’s Five Keys to Safer Food are: keep clean; separate raw and cooked; cook thoroughly; keep food at safe temperatures; use safe water and raw materials.

One in ten

WHO notes that 1 in 10 people fall ill from unsafe food each year. Review the keys with the Five Keys to Safer Food Checklist.

Ready.gov’s basic disaster supplies kit starts with water — one gallon per person per day for several days — and a several-day supply of non-perishable food, plus a radio, flashlight, first aid kit and the other items on the list.

Work out your quantities

Work out general planning quantities with the Emergency Preparedness Checklist. No medication module is included, and no personal medical preparation advice is given.

The world's 50 busiest airports in 2024 sit in 24 countries and territories, not 50 countries.

The directory and the rules

The directory carries the ranking — ranks 1–20 verified against ACI, ranks 21–50 DRAFT — and it is the only page on this site that carries the passenger figures. How airports protect traveller health explains the International Health Regulations points-of-entry rules and CAPSCA in plain language, with no per-airport rating, because no public per-airport rating exists.

Before, during and after flying

The traveller guides are Before you fly: health checks, At the airport and on the plane and After you land: symptoms to watch.

By region

The region pages are North America (17 airports), East Asia (14), South and Southeast Asia (7), Europe (8) and the Middle East and Latin America (4).