A team of scientists has developed a new way to visualize the contrasts in air pollution breathed around the world. The results reveal huge disparities in air quality, with the situation worsening in many countries.

But the new project also tells a positive story: targeted government action can lead to cleaner air.

Inspired by Ed Hawkins’ Climate Stripes, the new Air Quality Stripes show air pollution from 1850 to the present. Each year is a separate vertical bar colored according to the amount of particulate pollution. Air that meets World Health Organization guidelines is coded as sky blue. Shades of yellow, brown and black represent higher pollution in a color scheme that reflects more than 200 images of smog from around the world.

Dr Kirsty Pringle from the University of Edinburgh, who co-directed the project, said: “Air pollution is often referred to as the invisible killer, but these images make the invisible visible and show the changes over decades.”

The website allows you to generate your own air pollution stripes for major cities.

Dr Jim McQuaid from the University of Leeds, another co-director of the project, said: “For me it’s all about that one moment when someone gets it; that sudden ‘oh yes, now I get it’.”

The stripes for London and Beijing show the huge improvements that can come if action is taken.

For more than a century, London was plagued by coal-fired smog so thick it resembled pea soup. A reluctant government was finally forced to intervene when 12,000 people died in a week-long smog in 1952. Clean air laws followed. Coal was replaced by fuel oil, then fossil gas.

Beijing’s deteriorating air quality went largely unnoticed until the world’s eyes turned to the city for the 2008 Olympics. By then, China was already killing more than 2 million people a year from air pollution, but a recent cleanup of industry and traffic has shown rapid initial results.

Jakarta and Islamabad are examples of developing countries with rapid urbanization and industrial growth, but without corresponding measures on air pollution.

The data for the stripes comes from the UK Met Office’s global climate models, with adjustments based on satellite observations that first became available around 1998. This adjustment was also applied to past pollution, projected back to 1850 using fuel and energy statistics.

On their website, the responsible team notes: “There are few historical observations of PM2.5 from before the year 2000, so instead we use data produced by a mix of computer model simulations and satellite observations. For the most recent years (2000-2021) we use a dataset combining ground-level and satellite observations of PM2.5 concentrations from Van Donkelaar et al. (2021, V5 0.1 degree resolution), this dataset can be found here.”

They added: “Modelling global pollutant concentrations is a major challenge, and models are continually being evaluated and improved. Previous research has shown that the CMIP6 multi-model simulations often underestimate PM2.5 concentrations compared to global observations (Turnock et al, 2020).

“To address this issue and ensure a smooth time series between the model and the satellite data, we take the following steps: for each city, we first calculate a three-year (2000-2002) average of the satellite data for that city. We then calculate the three-year (2000-2002) average of the model concentrations for the same city. The ratio of these values ​​represents the bias of the model relative to observations. We then adjust (or “weight”) the model values ​​using this ratio. This is a similar approach to that of Turnock et al (2023) and Reddington et al (2023).”

Forecasts are made for each degree of longitude and latitude. For the UK this is approximately 60km (40 miles) by 110km (70 miles), so the bars cannot show the details of air pollution in each city, but they do illustrate the changes.

More than 99% of the world’s population still breathes air that does not meet World Health Organization guidelines. Even after improvements seen in Europe, particulate matter pollution still causes more than 400,000 premature deaths each year; for the UK, this figure is between 29,000 and 43,000.

Professor Ed Hawkins from the University of Reading, who designed the Climate Stripes, said: “The Climate Stripes have appeared on the white cliffs of Dover, on football kits and racing cars, at music festivals and during London Fashion Week.

“By making abstract data tangible, we can all play a role in solving some of the world’s biggest problems. Many major cities around the world still struggle with dirty air, but air quality is improving in other places. These are clear demonstrations that critical global problems can be solved with sufficient political will.”