Particle Pollution (PM)
Particle pollution, also called particulate matter or PM, is a mixture of solids and liquid droplets floating in the air. Some particles are released directly from a specific source, while others form in complicated chemical reactions in the atmosphere.
Particles come in a wide range of sizes. Particles less than or equal to 10 micrometers in diameter are so small that they can get into the lungs, potentially causing serious health problems. Ten micrometers is less than the width of a single human hair.
Fine particles (PM2.5) are 2.5 micrometers in diameter or smaller, and can only be seen with an electron microscope. Fine particles are produced from all types of combustion, including motor vehicles, power plants, residential wood burning, forest fires, agricultural burning, and some industrial processes.
Since they are so small and light, fine particles tend to stay longer in the air than heavier particles. This increases the chances of humans and animals inhaling them into the bodies. Owing to their minute size, particles smaller than 2.5 micrometers are able to bypass the nose and throat and penetrate deep into the lungs and some may even enter the circulatory system.
Studies have found a close link between exposure to fine particles and premature death from heart and lung disease. Fine particles are also known to trigger or worsen chronic disease such as asthma, heart attack, bronchitis and other respiratory problems.
On a very clear and non-hazy day, the PM2.5 concentration can be as low as 5 µg/m3 or below. The 24-hour concentration of PM2.5 is considered unhealthy when it rises above 35.4 µg/m3.
Good (0-50)
Moderate (51-100)
Unhealthy for Sensitive Groups (101-150)
Unhealthy (151 to 200)
Very Unhealthy (201-300)
Hazardous (301-500)
The coarse particles are between 2.5 and 10 micrometers (from about 25 to 100 times thinner than a human hair). These particles are called PM10. These particles cause less severe health effects mostly in the upper respiratory tract. These consist of smoke, dirt and dust from factories, farming and roads as well as mold, spores and pollen. They are made from crushing and grinding rocks and soil then blown by wind.
Exposure to such particles can affect both your lungs and your heart. Numerous scientific studies have linked particle pollution exposure to a variety of problems, including:
- premature death in people with heart or lung disease
- nonfatal heart attacks
- irregular heartbeat
- aggravated asthma
- decreased lung function
- increased respiratory symptoms, such as irritation of the airways, coughing or difficulty breathing.
People with heart or lung diseases, children, and older adults are the most likely to be affected by particle pollution exposure.
Good (0-100)
Moderate (101-250)
Poor (251-350)
Very Poor (351 to 430)
Hazardous (430+)
Nitrogen dioxide is the chemical compound with the formula NO 2. It is one of several nitrogen oxides. NO 2 primarily gets in the air from the burning of fuel. NO 2 forms from emissions from cars, trucks and buses, power plants, and off-road equipment.
The main effect of breathing in raised levels of nitrogen dioxide is the increased likelihood of respiratory problems. Nitrogen dioxide inflames the lining of the lungs, and it can reduce immunity to lung infections. This can cause problems such as wheezing, coughing, colds, flu and bronchitis.
Increased levels of nitrogen dioxide can have significant impacts on people with asthma because it can cause more frequent and more intense attacks. Children with asthma and older people with heart disease are most at risk.
Occurrence in air
Maximum 30-minute or 1-hour average and maximum 24-hour average outdoor nitrogen dioxide
concentrations of up to 940 µg/m3 (0.5 ppm) and 400 µg/m3 (0.21 ppm), respectively, have been
reported. Annual mean concentrations in urban areas throughout the world are generally in the range
2090 µg/m3 (0.010.05 ppm). Urban outdoor levels vary according to the time of day,
the season of the year and meteorological factors. Typical daily patterns comprise a low background
level on which are superimposed one or two peaks of higher levels that correspond to rush-hour
traffic emissions of nitrogen oxides.
Conversion factors
Nitrogen dioxide:
l ppm NO2 = 1880 µg/m3
l µg/m3 NO2 = 5.32 ~ 10-4 ppm
Sulfur dioxide is a gas. It is invisible and has a nasty, sharp smell. It reacts easily with other substances to form harmful compounds, such as sulfuric acid, sulfurous acid and sulfate particles.
About 99% of the sulfur dioxide in air comes from human sources. The main source of sulfur dioxide in the air is industrial activity that processes materials that contain sulfur, eg the generation of electricity from coal, oil or gas that contains sulfur. Some mineral ores also contain sulfur, and sulfur dioxide is released when they are processed. In addition, industrial activities that burn fossil fuels containing sulfur can be important sources of sulfur dioxide. Sulfur dioxide is also present in motor vehicle emissions, as the result of fuel combustion.
Sulfur dioxide affects human health when it is breathed in. It irritates the nose, throat, and airways to cause coughing, wheezing, shortness of breath, or a tight feeling around the chest. The effects of sulfur dioxide are felt very quickly and most people would feel the worst symptoms in 10 or 15 minutes after breathing it in.
Those most at risk of developing problems if they are exposed to sulfur dioxide are people with asthma or similar conditions.
Carbon monoxide (CO) is a colorless, odorless, and tasteless flammable gas that is slightly less dense than air. It is toxic to animals that use hemoglobin as an oxygen carrier (both invertebrate and vertebrate) when encountered in concentrations above about 35 ppm, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal biological functions. In the atmosphere, it is spatially variable and short lived, having a role in the formation of ground-level ozone.
The most common symptoms of CO poisoning are headache, dizziness, weakness, upset stomach, vomiting, chest pain, and confusion. CO symptoms are often described as 'flu-like'. If you breathe in a lot of CO it can make you pass out or kill you. People who are sleeping or drunk can die from CO poisoning before they have symptoms.
Average levels in homes without gas stoves vary from 0.5 to 5 parts per million (ppm). The maximum permissible exposure limit (PEL) for carbon monoxide is 50 parts per million (ppm) parts of air (55 milligrams per cubic meter (mg/m3)) as an 8-hour time-weighted average.
Ozone, or trioxygen, is an inorganic molecule with the chemical formula O 3. It is a pale blue gas with a distinctively pungent smell. It is an allotrope of oxygen that is much less stable than the diatomic allotrope O 2, breaking down in the lower atmosphere to O 2.
WHO states: "There are few epidemiological studies on the chronic effects of ozone on human health. Incidence of asthma, a decreased lung function growth, lung cancer and total mortality are the main outcomes studied. At levels currently observed in Europe, the evidence linking O 2 exposure to asthma incidence and prevalence in children and adults is not consistent. Available evidence suggests that long-term O 2 exposure reduces lung function growth in children. There is little evidence for an independent long-term O 2 effect on lung cancer or total mortality.
The plausibility of chronic damage to the human lung from prolonged O 2 exposure is supported by the results of a series of chronic animal exposure studies."
Air Quality Guide for Ozone
Good (0-50)
Moderate (51-100)
Unhealthy for Sensitive Groups (101-150)
Unhealthy (151 to 200)
Very Unhealthy (201-300)
Hazardous (301-500)