It is already more than one year since the World Health Organization has released their 'Ambient (outdoor) air pollution in cities database 2014'. The WHO team who worked on this project have done an excellent work at gathering the data for so many countries, and putting it all together in a single place accessible for all.

We wrote about it in several of our past articles (like for the Air Quality in Africa or in Latin America), but we never had the chance to look at the different options to visualize their data set. So, this is what we will be writing about in this article.

The first step for the visualization is to define the levels and associated colors. For this purpose, the WHO has already defined several concentration breakpoints for PM₁₀ and PM_2.5 annual concentrations, more known as the WHO "Air Quality Guidelines and Interim targets ", so we will just be reusing the same breakpoints values.

For the sake of the visualization, an extra level called "Significantly over target " is added, and defined as 150% of the concentration of the higher interim target (target level 3). Colors code are also assigned to each levels. The table on the right is summarizing the associations.

In order to plot the data for each country (There are 1622 from 92 countries in the WHO database), we use the country average concentration - weighted by the number of inhabitant in each cities. So, that, if the largest city is having a low AQI and few smaller cities in the same country are having a higher AQI, then the country national AQI levels should be reported as small to moderate.

In order to know the number of inhabitant for each city reported in the WHO database, we are using the service from geonames.org. Unfortunately, not all of the cities reported in the WHO DB can be matched on geonames.org, so the visualization below is not completely exact, but good enough for a proof of concept.

World Health Organization: Annual Ambient Air Pollution

And for the reference, here is the list of all countries with their respective annual weighted concentrations for PM10 and PM2.5 pollutants. The columns 'Inhabitants for the cities with Air Quality Data' refers to the total population obtained from the geonames.org service, for the city which can be reverse geo-coded.