Satellites see the pollution you can’t, and can help us solve the problem

April 26, 2021

Ukraine data map

If you were in space right now, what would the earth look like?

It would probably look the way it always looks like in pictures - a globe covered by large areas of blue ocean interspersed by green and brown land masses and swirling clouds.

What you wouldn’t see is the air we breathe, and how polluted it might be. Industrial production, transportation, human activity and natural causes all influence pollution levels, which are also affected by climate, temperature and weather patterns. Air pollution directly impacts the health of those with a predisposition to cardiovascular and respiratory diseases, but in reality it affects everyone’s health and prosperity. (The economic burden of pollution associated with premature mortality and morbidity is equivalent to five to 14 percent of countries' GDPs.)

On the ground, air pollution has to be significant to be noticed by the human eye, but that doesn’t mean it’s not “seen” from space.  In fact, satellites are capturing this “invisible to the eye” data, showing where the pollution is the worst.

Many countries already have machinery in place to collect data on air pollution, but these are often concentrated in cities and don’t reflect circumstances across the nation. Moldova’s national air monitoring system is updated daily, using information from 17 monitoring stations (based on manual sampling), but only a handful of cities and towns are covered by the system. The Ukrainian public network of air pollution sensors is also not producing enough, and its expansion is growing too slowly. Citizen-led projects are promising, but they have yet to cover the entire country and experts often doubt the reliability of those measurements.

So what about using those satellites to gather a more complete set of data? UNDP Moldova and UNDP Ukraine partnered with the European Space Agency and their EO Clinic programme to test the applicability of satellite data to understand air pollution and which regions are most vulnerable.

The research team used satellite data provided by Sentinel 5P – a cutting edge satellite technology equipped with latest technologies for atmospheric measurements - to analyse the main air pollutants: ozone (O3), nitrogen dioxide (NO2), sulphur dioxide (SO2) and particulate matter (PM10 and PM2.5). They were testing the applicability of satellite data to understand air pollution, how it changed during COVID lockdowns and which regions are most vulnerable – looking at the past three years.

Using this new data, the two countries were able to draw conclusions, published this past spring. Here’s a sample of what they found:


It’s no surprise that pollution hotspots were glaring in cities with heavy industry. The biggest polluters aligned with high nitrogen dioxide areas, and data showed these emitters might be more significant than other forms of pollution.

Particulate matter not only affects air in the locations of pollution, but risks affecting a far wider geographical range since it’s easily carried by the wind.  At Ukraine’s national level, the average annual concentration of PM2.5 of 10 μg/m3 was reached or exceeded in 16 out of 36 months monitored. Higher concentrations are observed in the spring and autumn months, which may lead to a 15 percent increase in mortality.

(The animation below shows how far can the dust be taken by wind from the source of origin.)

Day of the week and seasons also impacted the levels. Most cities surged on Fridays, for instance, and in winters the country sees almost a tenfold increase in the concentrations of nitrogen dioxide and sulphur dioxide compared to the summer period. 

Cities did experience a noticeable decline in air pollution during the quarantines imposed in response to Covid-19, most especially in the industrial areas.


Overall, the level of air pollution in Moldova shown in the study was relatively low compared to other European and neighboring countries. Concentrations of nitrogen dioxide was also low, with elevated levels in the capital, along the border with Ukraine and around power plants.

Like in Ukraine, seasons also had an effect in Moldova. Although the levels of sulphur dioxide were generally low, it’s mostly connected to coal-fired power stations, industrial processes or other fossil fuel burning activities. It naturally peaked during the winter (heating) period, increasing five to ten times compared to summer. 

While the country’s COVID-19 lockdown caused a serious economic downturn leading to cleaner air in some regions, it did not show considerable overall change in air pollution data.

(Read more details on the results from UNDP Moldova and UNDP Ukraine)

Seeing is believing

To complement the research project, two easy-to-read dashboards were developed, showcasing the results of the analysis. The interactive maps allow for switching between various pollutants and checking their concentrations of across Moldova during the last 2 to 3 years from the Sentinel 5P satellite and the Copernicus Atmosphere Monitoring Service.

Satellite data, while informative and able to cover areas without current monitoring, can lack precision or miss pollutants recognizable at local levels. It is best used in conjunction with locally collected sources, where it can also serve to validate citizen- or state-collected data.

The data can help inform policy to diminish the overall pollution levels and their health impact. This means a reduction of coal plants and subsidizing fossil fuels, while focusing on green economy targets and programs aimed at achieving them.

SDG11 includes an indicator on air pollution, for example, and the data could serve as an additional source of evidence for the assessment or help to increase confidence in local measurements. 

This is part of a series of articles on air pollution in Europe and Central Asia. Around the region, UNDP is working to tackle the problem of air pollution, from getting a sense of its breadth to finding the causes behind it to informing policy and encouraging greener development - so that everyone can breath cleaner air.