What is Particulate Matter and how does it get into the atmosphere?

PM are a complex mixture of solid and liquid particles of organic and inorganic substances suspended in the air. typically measured as PM₁₀ and PM_2.5 with diameters of 10μm (microns) or 2.5μm. PM is a common proxy indicator for air pollution.

It affects more people than any other pollutant. While particles  with a diameter of 10 microns or less, (≤ PM₁₀) can penetrate and lodge deep inside the lungs, the even more health-damaging particles are those with a diameter of 2.5 microns or less, (≤ PM_2.5). PM_2.5  can penetrate the lung barrier and enter the blood system. Chronic exposure to particles contributes to the risk of developing cardiovascular and respiratory diseases, as well as of lung cancer.

The major components of PM are sulfate, nitrates, ammonia, sodium chloride, black carbon, mineral dust and water. These particles can consist of direct emissions such as dust, emissions from combustion engines, from the burning of solid fuels or natural sources such as windblown salt, plant spores and pollens. These direct emissions are known as primary PM.

PM can also be produced indirectly by formation of aerosols through reactions of other pollutants such as Nitrogen Oxides (NO_X) and Sulphur Dioxide (SO₂); these are known as secondary PM. In Ireland, the main sources are solid fuel burning and vehicular traffic.

Air quality measurements are typically reported in terms of daily or annual mean concentrations of PM₁₀ particles per cubic meter of air volume (m³). Routine air quality measurements typically describe such PM concentrations in terms of micrograms per cubic meter (μg/m³). Concentrations of fine particles (PM_2.5 or smaller), are also reported.

Epidemiological studies show that the most severe health effects caused by air pollution are due to particulate matter, and to a lesser extent, to ozone. Inhalation of particulate matter causes irritation or damage to the pulmonary tissue. Particulate matter can cause both short and long-term health effects. According to the World Health Organisation (WHO), there is no safe threshold value below which no harmful effects occur. While short-term exposure to particulate matter complicates existing health problems such as respiratory infections and asthma, the health effects of long-term or chronic exposure are significantly more severe. Chronic exposure increases the risk of cardiovascular and pulmonary diseases and of lung cancer.

In addition, particulate matter has adverse effects on climate change and ecosystems. It contributes to the degradation of treated surfaces which therefore need to be cleaned more often (the so-called soiling effect) and has, depending on the composition, a corrosive effect on material and cultural heritage. Particulate matter has both a cooling (sulphate aerosols) and warming (black carbon) effect, and therefore also plays a role in climate change.

EU and WHO standards

PM10

PM2.5

The Ambient Air Quality Directive defines the PM2.5 Average Exposure Indicator (AEI). This indicator reflects population exposure to PM2.5 and shows the average concentration at urban background locations throughout a country. It is calculated as a 3-year average. In 2015, the level had to be below 20 µg/m³.