A range of historical air quality data is freely available on the IQAir platform, for each location it reports on. Here's how to access three main types of historical data:
1) Past 48h detailed hourly data
2) Past 30 days daily average data
3) Yearly and monthly average data since 2018, in IQAir's World Air Quality Reports
1 + 2) Past 48h detailed hourly data & 30 days daily average data
Within the IQAir website or mobile app, for any specific location you can scroll down the location's page until you find a historical data graph. Here, you can toggle between "Hourly" and "Daily", which will display either the past 48h of data in hourly averages, or the past 30 days in daily averages. You can also toggle between pollutant parameters to view the historical graph for each of these.
Hover your cursor over each bar in the graph to display the timestamp and value.
48h historical data
30 day historical data
3) IQAir's World Air Quality Reports
Since 2019, IQAir has published an annual "World Air Quality Report", summarising historical PM2.5 data for the previous year across global cities. These reports (covering years since 2018) include a global ranking of the world's most polluted cities for PM2.5 pollution, and are published alongside an interactive web-based dataset, which is free to explore on the IQAir website. Here, you can contrast locations' annual average PM2.5 levels over time, as well as view their monthly PM2.5 average values. Explore these below: