The new guide fixes the maximum recommended quantities of the most harmful atmospheric pollutants (particulate matter or particulate matter, ozone, nitrogen dioxide, sulphur dioxide and carbon monoxide) and, in almost all cases, the WHO has decided to lower the levels considered to be the safest.

The particulate matter considered to be the most dangerous for humans are those having a diameter of less than 2.5 microns (PM 2.5). So far, the WHO recommended in one day less than 25 micrograms per cubic meter of air inside the network. Now the optimal level drops to 15 micrograms. The measure could be taken in the case of Beijing, one of the most polluted cities in the world, where, for example, it often wakes up with more than 500 micrograms per cubic meter and in very bad days it has exceeded 1,000.

As for particles of larger size, diameter 10 microns (PM 10), the WHO has recommended its daily level, so far of 50 micrograms per cubic meter of air, which becomes 45 micrograms. The two types of microparticles, PM 2.5 and PM 10, come from burning fossil fuels and are considered dangerous to health because they can enter the lungs, but the former are even more harmful, as their size is small and can reach the bloodstream.

According to the WHO, 90% of PM2.5 related deaths can be prevented by the new guide. These measures are not mandatory in principle by law, but according to the organization they are highly recommended both to protect health and to combat climate change.