The three most polluted cities in the world
1. Lima, Peru – 6.35 out of 10
-Air quality score – 187/500
-Congestion level – 42%
-Emissions per person – 1.8 Mt COE2e
The most polluted city on our list was Lima, Peru, largely due to the fact that it has by far the worst air quality score, at 187. Air pollution has long been a problem in the Peruvian capital, so much so that the government has created an alert system, which when at its highest level, means that children, pregnant women and the elderly are not allowed to leave their homes, while others must cover their mouths and noses. The city also scored highly for vehicle congestion (at 42%), which is one of the big contributors to the previously mentioned air pollution problems.
2.Bogotá, Colombia – 5.4 out of 10
-Air quality score – 82/500
-Congestion level – 53%
-Emissions per person – 1.6 Mt COE2e
Another South American city takes second place, Bogotá in Colombia. Bogotá was the city with the highest level of traffic congestion of those which we looked at, with 52% (this means that an average journey would take 52% longer than in uncongested conditions). Such levels of vehicle emissions clearly cause a lot of pollution, alongside those from the industrial combustion in the city too.
3.Santiago, Chile – 5.27 out of 10
-Air quality score – 161/500
-Congestion level – 31%
-Emissions per person – 3.2 Mt COE2e
Yet another South American capital completes the top three most polluted cities on our list, with Santiago in third place. The Chilean capital had one of the worst air quality scores, at 161 (second only to Lima) and alongside the usual causes of pollution such as vehicle emissions, Santiago isn’t helped by the many mountains that populate Chile, which trap contaminants.
The three least polluted cities in the world
1.Reykjavík, Iceland – 1.9 out of 10
-Air quality score – 17/500
-Congestion level – 16%
-Emissions per person – 2.8 Mt COE2e
At the other end of the scale, here are some of the countries on our list which have the lowest levels of pollution and emissions, starting with Reykjavík in Iceland. Iceland is a generally environmentally conscious country with a heavy reliance on clean geothermal energy and also has a very low population density, making it one of the least polluted industrialized countries in the world.
2.Ravenna, Italy – 1.91 out of 10
-Air quality score – 36/500
-Congestion level – 14%
-Emissions per person – 0.1 Mt COE2e
Narrowly behind Reykjavík is the Italian city of Ravenna, located in Emilia-Romagna. Incredibly, the city has emissions of just 0.1 metric tons per person and also scored well in the other two factors too, with an air quality score of 36 and congestion level of 14%.
3.Aarhus, Denmark – 1.94 out of 10
-Air quality score – 13/500
-Congestion level – 20%
-Emissions per person – 0 Mt COE2e
Aarhus is located on Denmark’s Jutland peninsula and has invested significantly in recent years in aiming to become CO2-neutral and independent of fossil fuels for heating by 2030. And it’s clearly paying off, with emissions of just 1,900, which equates to less than 0.1 metric tons per person in the city!
Air quality – Lima (187 air quality score)
The city with the worst air quality (by some distance) was Lima, which also was the worst city overall in our ranking. The AQI score we used gives countries with worse air quality a higher score, which is calculated based on the prevalence of PM2.5 particles in the atmosphere.
Congestion – Bogotá (53%)
Bogotá in Colombia had the worst traffic congestion of the cities which we looked at, which of course contributes greatly to the level of pollution in the city. A congestion level of 53% means that an average 30-minute journey in the city takes 53% longer than it would do in the streets were free of congestion.
Emissions – Rotterdam (50.5 metric tons per person)
The city with the highest level of carbon dioxide equivalent emissions per person was Rotterdam in the Netherlands, with 50.5 metric tons per person. A large reason for this is the fact that Rotterdam is Europe’s largest seaport and is a major industrial city.
Methodology
We ranked the above cities on the following three factors, giving each city a normalised score out of ten for each factor before taking an overall average across all three factors. Note that data on all three factors was only available for the cities shown below and that other cities may rank worse for individual factors, the cities used above are the only ones that appeared in all three datasets below.
Air quality
The Air Quality Index (AQI) score according to IQAir, which gives each city a score based on the concentration of PM2.5 particles in their atmosphere. Note that a higher score here indicates worse air quality.
Congestion
The congestion level according to TomTom’s Traffic Index 2020. The index gives a congestion level percentage which is calculated by analysing travel times for free-flow traffic in the city, before calculating how much extra time drivers spend on average during a 30-minute rush hour trip.
Emissions
The level of carbon dioxide equivalent emissions in each city divided by the population, sourced from Global Carbon Atlas data.
All data correct as of May 2021.
