PM10 is the mass of all particles in a specific volume of air (usually in μg/m3, micrograms per cubic metre of air) with a diameter of less than 10 micrometres (μm), i.e. the particle sizes that can penetrate our lower airways. PM2.5 is the mass of all particles with a diameter of less than 2.5 micrometres in a specific volume of air. It was demonstrated in the 1990s that the relationship between particulate matter and health was even stronger if the measure PM2.5 was used. The choice of 2.5 micrometres was rather coincidental due to shortcomings in the measurement technique available when monitoring started. Particles that have been inhaled can penetrate deep into the lungs and in some cases also pass through the blood- stream to the liver, brain and kidneys. There are several different ways in which particles can contribute to disease. The risk of inflammation and oxidative stress (damage caused by reactive oxygen species) increases as does the impact on the autonomic nervous system. There are also signs that particles can affect the ability of blood vessels to increase blood flow in the event of oxygen deficiency and affect the blood’s clotting ability. three sentences for a card from supernotecard