IAQ UK is an independent organisation with the aim of 'raising the agenda of indoor air quality within the home and workplace'

IAQUK Resources - Particulate Matter

Sources of Pollution


There are a wide range of particulate matter sources.  Some particulates may enter a building from external sources, such as industrial processes, vehicle emissions, air turbulence, lawn moving, wood/coal stoves, fires, cigarette smoke.  


Indoor particles may be generated from a material such as talc, floor and other sources of fine powder products.


Health effects

2.5 microns lead to high plaque deposits in arteries, causing vascular inflammation and atherosclerosis — a hardening of the arteries that reduces elasticity, which can lead to heart attacks and other cardiovascular problems.


Researchers suggest that even short-term exposure at elevated concentrations could significantly contribute to heart disease. If the particle is small and it gets very far into the lungs, special cells in the lung trap the particles and then they can't get out and this can result in lung disease, emphysema, lung cancer.


Health effects can include the following:

  • Coughing, wheezing, shortness of breath 
  • Aggravated asthma
  • Lung damage (including decreased lung function and lifelong respiratory disease)
  • Premature death in individuals with existing heart or lung diseases


The finer particles pose the greatest threat to human health because they can travel deepest into the lungs.


Particles are deposited in the lungs by one of four different ways: interception, impaction, sedimentation, and diffusion.



A particle is intercepted or deposited when it travels so close to a surface of the airway passages that an edge of the particle touches the surface. This method of deposition is most important for fibres such as asbestos. The fibre length determines where the particle will be intercepted.   For example: fibres with a diameter of 1 micrometre (µ) and a length of 200 µ would be deposited in the bronchial tree.



When particles are suspended in air, they have a tendency to travel along their original path. When there is a bend in the airway system, for example, many particles do not turn with the air but rather impact or stick to a surface in the particles' original path. The likelihood of impaction depends on the air velocity and the particle mass.



As particles travel through air, gravitational forces and air resistance eventually overcome their buoyancy (the tendency for the particle to stay up). The result is that the particles will settle on a surface of the lung. This type of deposition is most common in the bronchi, and the bronchioles. Sedimentation is not an important factor when the aerodynamic diameter of the particle is less than 0.5µ. Aerodynamic diameter is the diameter of a spherical particle that has the same settling velocity as another particle regardless of its shape, size or density. Using aerodynamic diameters allows occupational hygiene specialists to compare particles of different sizes, shapes and densities in terms of how they will settle out of the air flow stream.



The random motion of particles is similar to gas molecules in the air when particles are smaller that 0.5 µm. When particles are in random motion, they deposit on the lung walls mostly by chance. This movement is also know as the "Brownian motion". The smaller the particle size, the more vigorous the movement is. Diffusion is the most important mechanism for deposition in the small airways and alveoli.

Methylene Chloride breaks down into carbon monoxide (CO) in your body. CO can cause nervous system effects like those described above. Smoking also puts CO in your blood, so smokers can have these symptoms at lower Methylene Chloride levels than non-smokers.


CO also stresses the heart, and people with angina (chest pains) from coronary artery  disease are extremely sensitive to CO; Methylene Chloride can make angina worse, even with exposures below the limits. People with heart or lung conditions, smokers, people who are overweight or pregnant, and people with other exposure to carbon monoxide should limit their exposures to Methylene Chloride.

Particulates, alternatively referred to as particulate matter (PM) or fine particles, are tiny subdivisions matters of solid or liquid or a mixture of both, that are small enough to be carried by the air and therefore be breathed in by people, penetrating deep into lungs and causing damage.


Particulates may be seen as the most critical of all pollutants, and some estimates have suggested that indoor and outdoor particulates are responsible for up to 10,000 premature deaths in the UK each year.

Particulate Matter

The solid particles come in numerous shapes and sizes and may be composed of different chemical components.  They are divided into two principal groups:


Course particles are less than 10 microns (µm) and more than 2.5 microns in diameter and can penetrate into the respiratory system and lung and can cause damage. One micron ormicrometer, is one millionth of a meter or approximately 1/25,000 of an inch. These particles are about 25 to 100 times thinner than a human hair.


Fine particles measure 2.5 microns or less in size (approximately 1/30th the diameter of a human hair) and can penetrate deep into the body’s respiratory system.


Large particles (above 10 micron) are generally filtered out through the airways’ natural  mechanisms. Nasal hairs (vibrissae) at the opening of the nostrils trap large particles of dust that might otherwise be inhaled. The entire respiratory system, is lined with a mucous membrane that secretes mucus. The mucus traps smaller particles like pollen or smoke. Hair like structures called cilia line the mucous membrane and move the particles trapped in the mucus out of the nose.  The mucous leaves the airway by coughing or swallowing.


The 10 micrometer size does not represent a strict boundary between respirable and non-respirable particles, but has been agreed upon for monitoring of airborne particulate matter by most regulatory agencies.


The smallest particles, less than 100 nanometers may be even more damaging to the cardiovascular system. (A nanometer is one-billionth of a meter, a billion is a thousand times bigger than a million). There is evidence that particles smaller than 100 nanometers can pass through cell membranes and migrate into other organs, including the brain. It has been suggested that particulate matter can cause similar brain damage as that found in Alzheimer patients. Particles emitted from modern diesel engines (commonly referred to as Diesel Particulate Matter, or DPM) are typically in the size range of 100 nanometers (0.1 micrometer).




A particulate matter sampler is an instrument for measuring the properties (such as mass concentration or chemical compostion) of particulates in the ambient air.


Total suspended particulate matter (TSP) monitoring is used to determine the total amount of suspended particular material present in the atmosphere.  It will not determine the type of particulates. Total suspended particulate matter (TSP) is measured using a high-volume air sampler that draws a large known volume of air through a pre-weighed filter for a determined timescale. After sampling, the filter is re-weighed and the difference in filter weight is the particulate mass. The concentration of TSP in the air is calculated as the particulate mass divided by the volume of air sampled. The particulate matter retained on the filter can be analysed to determine the concentration of other pollutants, such as lead or other metals. The design of the air inlet means that airborne particles with diameters greater than a pre-determined micron size are unlikely to be drawn into the sampler.


Gravimetric Methods

An air pump draws ambient air at a constant flow rate into a specially shaped inlet where particulate matter is separated into size fractions. Particulate matter is then collected on a filter. Each filter is weighed before and after use, to determine the net mass gain due to collected matter. The total volume of air filtered is known from the constant air flow, and the difference in filter weights is used to calculate the particulate matter concentration.


Beta Attenuator Methods

Beta rays are radiation emitted by electrons and a sensor is used to count the electrons.  As air is drawn through the sample system, the dust particles contained in the air are deposited onto a filter.  As the layer of dust builds up it weakens the intensity of the beta beam and reduces the electron count. The attenuation measurement converts to a measure of the mass on the filter, so that the filters do not require later laboratory analysis for the mass variable.


Tapered Element Oscillating Microbalance

Air is drawn through a filter mounted on a vibrating glass tube. The element oscillates according to a characteristic frequency, as PM10 particles get trapped on the filter the additional weight changes the oscillating frequency of the tube. This frequency change is converted into a particulate mass that can be divided by the volume of air being drawn into the instrument to produce a PM10 concentration. TEOM samplers operate on a continuous basis and do not need filter changes as frequently as high-volume air samplers. An advantage of continuous monitoring is that it can provide additional information, such as the time of day that peak concentrations occurred. Such information may be used in conjunction with meteorological data to help identify the source of an emission.

Recent epidemiological research suggests that there may be no threshold below which health effects do not occur.


The health effects include:

  • Toxic effects by absorption of the dust into the blood (eg lead, cadmium, zinc)
  • Allergic or hypersensitivity effects (eg some woods, flour grains, chemicals)
  • Bacterial and fungal infections (from live organisms)
  • Fibrosis (eg asbestos, quartz)
  • Cancer (eg asbestos, chromates)
  • Irritation of mucous membranes (eg acid and alkalis)
  • Long-term deleterious effects on lung function causing marginally increased death rates and sickness in sensitive people


The factors that influence the health effects are:

  • The composition of the dust and its health effects
  • The concentration of the dust
  • The size of the dust (smaller particles tend to have more severe effects because they may be inhaled more deeply into the lungs)
  • The duration of exposure (possibly in years)


Some people, such as the elderly and people with respiratory and cardiovascular diseases, are more susceptible than others to the effects of PM. Susceptible groups include children and adults with asthma, bronchitis, and respiratory infections. Researchers are working to better understand the factors leading to increased susceptibility to PM health effects.



Children may be especially vulnerable to exposure to PM and other air contaminants because they breathe more air per pound of body weight relative to adults.


In addition, people of all ages who are active outdoors may be at increased risk because during physical activity greater amounts of PM may penetrate into deep parts of the lung that are vulnerable to injury. For example, children and adults who play in outdoor sports teams and participate in other outdoor physical activities may be at increased risk.