Types, Sources and Consequences of Air Pollution
Air pollution is caused mainly by gases, particles, and to a lesser extent liquid droplets. These can act as vehicles for seriously nasty pollutants such as heavy metals and dioxins. I am trying to keep this wide ranging despite my own more specialised interests.
Pollutant Gases can be poisonous when concentrated, or irritant when diffuse.
Carbon Dioxide
Is produced when any carbon based substance or fuel is burnt. Coal, wood, gas, diesel, jet fuel, bunker oil, petrol, fuel oils, forest fires.
Is not poisonous as such and only dangerous to humans and land animals if concentrated when it excludes oxygen.
I class it as a pollutant firstly because it harms just about everything indirectly by enhancing the greenhouse effect and so causing global warming; and secondly because it dissolves readily in water including seawater, and wreaks havoc with sea life that has calcium carbonate in its structure so shellfish, some algae, coral reefs, etc.
Methane
Is produced mainly by decomposition processes, animal flatulence, with ocean warming from frozen methane hydrates, and from frozen methane as permafrost melts. Methane has no health effects as such, it is flammable as it is the same substance as domestic and industrial natural gas. So whether you call it a pollutant I accept is arguable. The real problem with methane is that it is a highly potent greenhouse gas, 100 times more potent than carbon dioxide, so contributing to global warming, see for example https://en.wikipedia.org/wiki/Atmospheric_methane.
Oxides of Nitrogen
Are also the consequences of burning, where any high temperature combustion process naturally tends to combine oxygen and nitrogen from the air into various oxides, usually as a mixture of oxides usually referred to as NOx. These are reactive gasses, and can cause or exacerbate respiratory and cardiac problems, and increase infant mortality. With ultra violet light in strong sunlight, they can react with other pollution such as car exhaust to create ozone. They can react with rain to form dilute nitric acid, which can both acidify and fertilise soils, causing environmental damage and encouraging rank growth and damage to sensitive sites. There is a lot of relevant literature on this, for example see https://www.gov.uk/government/publications/nitrogen-dioxide-health-effects-of-exposure and http://www.apis.ac.uk/overview/pollutants/overview_NOx.htm
Ozone
Linked to NOx as above. Ozone at ground level is a lung irritant, causing problems for those with asthma or COPD, etc, particularly the elderly and babies. It can also damage vegetation. Relevant literature includes https://www.epa.gov/ozone-pollution , http://www.yourlunghealth.org/healthy_living/pollution/outdoor/effects/, https://uk-air.defra.gov.uk/assets/documents/reports/aqeg/aqeg-ozone-report.pdf , and more online.
Sulphur Dioxide
Is mainly produced by the combustion of dirty fuels such as coal and cheaper grades of fuel oil, traffic, and some industrial processes. It is used commercially as a preservative, for example, for wine and dried fruits as E220. But in the air it is a serious pollutant particularly as it dissolves easily in any water based liquid forming dilute sulphuric acid. Health effects include, again, respiratory problems for children and the elderly. It can also seriously damage trees. it is spread either as a gas in the atmosphere, or on the surfaces of fine particulates (see below).
See https://www.epa.gov/so2-pollution/sulfur-dioxide-basics#effects and from Spain, http://www.mma.gob.cl/retc_ingles/1316/w3-article-51518.html
Particulates may be inert but are usually not, and act as vehicles for other serious pollutants which adhere to particle surfaces. But the real harm to health comes from the fine particulates, commonly referred to as "PM", with sizes quoted in microns - millionths of a metre of thousandths of a millimetre. So PM1, PM2.5, PM10, with EU and UK law prescribing limits for PM2.5 and PM10. Particles this fine generally behave as an aerosol, meaning they disperse as if they were a gas. Particles from combustion are typically carbon or metallic, and may be smooth or rough.
Particles are ingested by inhalation. PM10 tends to accumulate in the lungs, whereas PM2.5 and below can pass through the lungs directly into the blood stream. Fine particles have been discovered in the brain during autopsies, and it has been shown recently that PM1 and finer can travel up the path of the olfactory nerve which is the shortest path from the nose to the brain, e.g. see here.
Pollutant Gases can be poisonous when concentrated, or irritant when diffuse.
Carbon Dioxide
Is produced when any carbon based substance or fuel is burnt. Coal, wood, gas, diesel, jet fuel, bunker oil, petrol, fuel oils, forest fires.
Is not poisonous as such and only dangerous to humans and land animals if concentrated when it excludes oxygen.
I class it as a pollutant firstly because it harms just about everything indirectly by enhancing the greenhouse effect and so causing global warming; and secondly because it dissolves readily in water including seawater, and wreaks havoc with sea life that has calcium carbonate in its structure so shellfish, some algae, coral reefs, etc.
Methane
Is produced mainly by decomposition processes, animal flatulence, with ocean warming from frozen methane hydrates, and from frozen methane as permafrost melts. Methane has no health effects as such, it is flammable as it is the same substance as domestic and industrial natural gas. So whether you call it a pollutant I accept is arguable. The real problem with methane is that it is a highly potent greenhouse gas, 100 times more potent than carbon dioxide, so contributing to global warming, see for example https://en.wikipedia.org/wiki/Atmospheric_methane.
Oxides of Nitrogen
Are also the consequences of burning, where any high temperature combustion process naturally tends to combine oxygen and nitrogen from the air into various oxides, usually as a mixture of oxides usually referred to as NOx. These are reactive gasses, and can cause or exacerbate respiratory and cardiac problems, and increase infant mortality. With ultra violet light in strong sunlight, they can react with other pollution such as car exhaust to create ozone. They can react with rain to form dilute nitric acid, which can both acidify and fertilise soils, causing environmental damage and encouraging rank growth and damage to sensitive sites. There is a lot of relevant literature on this, for example see https://www.gov.uk/government/publications/nitrogen-dioxide-health-effects-of-exposure and http://www.apis.ac.uk/overview/pollutants/overview_NOx.htm
Ozone
Linked to NOx as above. Ozone at ground level is a lung irritant, causing problems for those with asthma or COPD, etc, particularly the elderly and babies. It can also damage vegetation. Relevant literature includes https://www.epa.gov/ozone-pollution , http://www.yourlunghealth.org/healthy_living/pollution/outdoor/effects/, https://uk-air.defra.gov.uk/assets/documents/reports/aqeg/aqeg-ozone-report.pdf , and more online.
Sulphur Dioxide
Is mainly produced by the combustion of dirty fuels such as coal and cheaper grades of fuel oil, traffic, and some industrial processes. It is used commercially as a preservative, for example, for wine and dried fruits as E220. But in the air it is a serious pollutant particularly as it dissolves easily in any water based liquid forming dilute sulphuric acid. Health effects include, again, respiratory problems for children and the elderly. It can also seriously damage trees. it is spread either as a gas in the atmosphere, or on the surfaces of fine particulates (see below).
See https://www.epa.gov/so2-pollution/sulfur-dioxide-basics#effects and from Spain, http://www.mma.gob.cl/retc_ingles/1316/w3-article-51518.html
Particulates may be inert but are usually not, and act as vehicles for other serious pollutants which adhere to particle surfaces. But the real harm to health comes from the fine particulates, commonly referred to as "PM", with sizes quoted in microns - millionths of a metre of thousandths of a millimetre. So PM1, PM2.5, PM10, with EU and UK law prescribing limits for PM2.5 and PM10. Particles this fine generally behave as an aerosol, meaning they disperse as if they were a gas. Particles from combustion are typically carbon or metallic, and may be smooth or rough.
Particles are ingested by inhalation. PM10 tends to accumulate in the lungs, whereas PM2.5 and below can pass through the lungs directly into the blood stream. Fine particles have been discovered in the brain during autopsies, and it has been shown recently that PM1 and finer can travel up the path of the olfactory nerve which is the shortest path from the nose to the brain, e.g. see here.
Substances carried by particulates
Heavy Metals
These include arsenic, cadmium, cobalt, nickel, lead, antimony, vanadium, zinc, platinum, mercury, palladium and rhodium. They can be present naturally in soil, but more commonly on sites used by old industries. They are often present to a varying extent in coal. They can get into the food chain if plants are grown on contaminated soil, in groundwater, and as air pollution through burning of coal, and from waste incinerators. The usual transport mechanism is by foods, both vegetable but particularly some fish, on the surface of fine particulates (see below). In simple summary, heavy metals are extremely poisonous, each in its own way, and tend to bio accumulate i.e. are not excreted effectively. See also https://en.wikipedia.org/wiki/Toxic_heavy_metal and https://academic.oup.com/bmb/article/68/1/167/421303
Dioxins and Furans
TOMPS
Heavy Metals
These include arsenic, cadmium, cobalt, nickel, lead, antimony, vanadium, zinc, platinum, mercury, palladium and rhodium. They can be present naturally in soil, but more commonly on sites used by old industries. They are often present to a varying extent in coal. They can get into the food chain if plants are grown on contaminated soil, in groundwater, and as air pollution through burning of coal, and from waste incinerators. The usual transport mechanism is by foods, both vegetable but particularly some fish, on the surface of fine particulates (see below). In simple summary, heavy metals are extremely poisonous, each in its own way, and tend to bio accumulate i.e. are not excreted effectively. See also https://en.wikipedia.org/wiki/Toxic_heavy_metal and https://academic.oup.com/bmb/article/68/1/167/421303
Dioxins and Furans
TOMPS