The live Major Cities Ranking (or just 'Ranking', as seen on our app) is made up of approximately 120 major cities and includes some of the largest and most well-known metropolises around the world, ordered according to AQI (Air Quality Index). The data used to generate the live ranking is aggregated from thousands of regulatory air quality monitoring stations and low-cost air quality sensors operated by governmental bodies, research institutions, non-profit organizations, companies, and citizen scientists. The number shown for each major city is the average (median) Air Quality Index (AQI) from all the stations in that city for that particular time. The Live Major Cities Ranking updates at least once per hour to reflect the changing air quality conditions in major cities around the world.

The goal of the major cities ranking is to provide a simple snapshot of the real-time air quality conditions of the most popular urban hubs. Comparing the air quality of only major cities rather than an exhaustive list of all cities provides a concise, meaningful and eye-opening comparison of air quality in urban centers across the globe.

The immediacy of the ranking is able to highlight the impact of events like wildfires, biomass burning, industrial activity, sandstorms and inversion weather events on the air quality in a city.

The Live Major Cities Ranking can be accessed either on the website or air quality app (Android or iOS).

In addition to the Live Major Cities Ranking, IQAir also provides Annual Historic Rankings for PM2.5 for over 7800 cities, which are the basis for the Annual World Air Quality Report.