Air pollution is a critical factor for human health and the terrestrial environment. According to a 2019 WHO estimate, ambient (outdoor) air pollution has caused 4.2 million premature deaths worldwide (WHO, 2022). The risk of adverse health effects depends on a person's health status, the pollutant type and concentration, and the length of exposure to the polluted air. For instance, people with heart or lung diseases, children, and the elderly are considered to be the most vulnerable groups. Figure 1.1, Table 1.1, and the text below provide information on the sources, conditions, and health effects of the following air pollutants: particulate matter, ultrafine particulate matter, ozone, nitrogen dioxide, carbon monoxide, and sulphur dioxide. Particulate matter fractions considered in this module include: inhalable coarse particles (with a diameter of 10 µm or less; PM10), fine particles (with a diameter of 2.5 or 1.0 µm or less; PM2.5, PM1), and ultrafine particles (with a diameter of 100 nm or less; PM0.1).
Before taking a closer look at the most common sources, you can test your current knowledge with the following question:
Table 1.1: Sources of key air pollutants: particulate matter (PM), ozone (O3), nitrogen dioxide (NO2), carbon monoxide (CO), and sulphur-dioxide (SO2) (Abelsohn, A. and Stieb, D.M., 2011).
| POLLUTANT |
SOURCE |
CONDITIONS |
| PM |
Traffic
Forest fires
Domestic biomass burning
Desert dust
|
Summer and winter |
| Ultrafine PM (<0.1 µm) |
Diesel traffic |
Close to busy roads |
| O3 |
Photochemical reactions between oxides of nitrogen (NOx) and volatile organic compounds (VOCs) |
Summer afternoons; heat and sunshine
|
NO2
CO
|
Traffic
Forest fires |
Close to busy roads |
| SO2 |
Industrial plants, including combustion and refining of coal, oil, and metal-containing ores, gasoline (although sulphur content has recently decreased) |
Close to industrial sources |
While Table 1.1 lists five key air pollutants, this training module will focus mainly on particulate matter, ozone, and nitrogen dioxide. Carbon monoxide, sulphur dioxide, and ammonia are only briefly described here, because we consider these to be less relevant for this training module. Carbon monoxide and sulphur dioxide emissions have decreased significantly in most of Europe, except for a few hotspots. Carbon monoxide levels from traffic are clearly high in large cities; additionally, high concentrations are found in and near harbours, caused not only by emissions from road traffic, but also by ship emissions. Less common hotspots include forest fires. The concentration levels of sulphur dioxide, in most of Europe, have decreased significantly since about 1990. A major but rare source of sulphur dioxide is a volcanic eruption. In Europe, relatively small eruptions occur frequently in Italy and Iceland. However, even in the case of a large eruption, only in the vicinity of the volcano do these emissions affect the air quality at breathing height. For further reading we refer to the EUMETRAIN module on volcanic ash. Ammonia is an important precursor of secondary inorganic aerosols, which contribute to PM2.5. As with sulphur dioxide, ammonia emissions have decreased in most of Europe, however, locally high concentrations in the atmosphere and deposition on land in ecologically vulnerable areas are still problematic.
