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Smoke (particulate matter)


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[top] [end]What is smoke or Particulate Matter?

Particulate matter -- particulates or PM for short -- refers to the many types and sizes of particles suspended in the air we breathe to public health are the particles small enough to be inhaled into the deepest parts of the lung. These small particles are known as PM10 (less than 10 microns in diameter) and even finer particles are known as PM2.5 (less than 2.5 microns in diameter). For comparison, a human hair is about 75 microns in diameter.

Particulate matter is a combination of fine solids such as dirt, soil dust, pollens, molds, ashes, and soot; and aerosols that are formed in the atmosphere from gaseous combustion by-products such as volatile organic compounds, sulfur dioxide and nitrogen oxides. Particulate matter is unique among atmospheric constituents in that it is not defined on the basis of its chemical composition. It may include a broad range of chemical species, including: elemental and organic carbon compounds; oxides of silicon, aluminum and iron; trace metals; sulphates; nitrates and ammonia. It is further classified as primary (emitted directly into the atmosphere) or secondary (formed in the atmosphere through chemical and physical transformations). The principal gases involved in secondary particulate formation are sulphur dioxide (SO2), nitrogen oxides (NOx), volatile organic carbons (VOCs) and ammonia (NH3). Primary particles are found in both the fine and coarse fractions, whereas secondary particles, such as sulphates and nitrates, are found predominantly in the fine fraction. Both primary and secondary PM can result from either natural or (human anthropogenic sources). Particulate matter air pollution comes from such diverse sources as motor vehicles, wood-burning stoves and fireplaces, construction activity, agriculture, industrial smokestacks, wildfires and other burn activity, and windblown dust from open lands.

[top] [end]Why should you be concerned about PM?

Particulate matter not only impairs visibility, it also poses a serious health. Our respiratory systems are equipped to filter out larger particles. However, the lungs are vulnerable to particles less than 10 microns in diameter (PM10), which can slip past the respiratory system's natural defenses. Very tiny particles (PM2.5) can penetrate deeply into the lungs and do the most harm.

The particulates we breathe enter the lungs and pass through progressively smaller airways until they reach the alveoli, tiny air sacs where oxygen enters the blood stream. Particulates that get trapped in these most sensitive tissues interfere with oxygen uptake. Toxic and cancer-causing compounds can "hitchhike" into the lung on these particulates and be directly absorbed into the lungs. Particulate matter air pollution is among the most harmful of all air pollutants. When inhaled, these particles evade the respiratory system's natural defenses and lodge deep in the lungs. Particulate matter is especially harmful to people with lung disease such as asthma and chronic obstructive pulmonary disease (COPD), which includes chronic bronchitis and emphysema, as well as people with heart disease. Exposure to particulate air pollution can trigger asthma attacks and cause wheezing, coughing, and respiratory irritation in individuals with sensitive airways.

Recent research has also linked exposure to relatively low concentrations of particulate matter with premature death. Those at greatest risk are the elderly and those with pre-existing respiratory or heart disease.

Particles of special concern to the protection of lung health are PM 2.5. These are known as fine particles and mainly come from motor vehicle exhaust. Fine particles are easily inhaled deeply into the lungs where they can be absorbed into the bloodstream or remain embedded for long periods of time. A recent study showed a 17 percent increase in mortality risk in areas with higher concentrations of small particles.



[top] [end]What are the health effects of PM air pollution?

PM air pollution can cause coughing, wheezing, and overall decreased lung function in otherwise healthy children and adults. Particulate pollution can trigger asthma attacks and respiratory illness in the more sensitive subgroups of the population, such as the elderly and those with heart and lung disease. Children are more susceptible to particulates because they have smaller lungs and less mature immune systems. In the past 10 years, more than two dozen health studies have linked high concentrations of particulate air pollution with an increase in emergency room visits, hospital admissions, and even premature death.

[top] [end]What causes PM air pollution?

PM is introduced to the air through both natural and human causes. The primary sources of PM excluding agricultural dust, are motor vehicles; diesel trucks and buses; residential wood stoves and fireplaces; industrial emissions; agricultural, slash and yard waste burning; PM concentrations tend to be especially high in area with greater population density, nearby industries or agriculture, or where local topography or weather conditions contribute to air stagnation.

[top] [end]Impacts on human health

The likelihood of an adverse response to particles is influenced by the degree of exposure, defined as any contact between a pollutant at a specified concentration and the outer (e.g., skin) or inner (e.g., respiratory tract epithelium) surface of the human body. Changes in the degree of exposure are influenced by the duration, magnitude and frequency of exposure. Inhalation is the only PM exposure pathway to considered in this assessment.

Ambient concentrations of particles are typically measured over a 24 hour sampling period, as described above. Over a 24 hour period, a person spends their time in many locations or microenvironments. For example, most people spend a great deal of time in indoor environments, at home and at work; some time each day in vehicles; and relatively little time each day outdoors. The proportion of time spent in different environments will vary with age, gender and day of the week. To the extent that microenvironmental PM concentrations are different from outdoor concentrations, population (and individual) exposures to PM will be different from those estimated from ambient monitoring data. The high correlations that have been found between personaexposure and indoor PM concentrations, combined with the amount of time spent indoors, indicate that indoor microenvironments are the most important contributors to PM exposure.

Indoor levels of particles are a function of: indoor sources, outdoor particle levels, the fraction of ambient air penetrating indoors, filtration, air exchange (e.g., older houses tend to be more leaky), particle decay and resuspension rates (e.g. from vacuuming or dusting). The latter source, the so-called 'Pigpen' or 'personal cloud' effect, helps explains why actual personal exposure is usually greater than indirect estimates combining indoor and outdoor concentrations and time-activity information. The increase in particle concentration as a result of a person occupying the microenvironment is overlooked.

Several early studies indicated that penetration of ambient air into indoor environments is more effective for fine particles than coarse particles. Some more recent studies have indicated that penetration factors for both fine and coarse particles are close to unity. Nonetheless, current scientific thinking maintains that small particles penetrate indoors more effectively than larger particles. In Canada, where building construction emphasizes energy efficiency, and therefore low air exchange rates, the fractions of fine and coarse particles of ambient origin that will be found indoors under equilibrium will tend toward 50% or less, particularly in the winter. Once inside, the larger particles tend to settle out more quickly than smaller particles; however, the larger particles are more easily resuspended as a result of indoor activities.

Cigarette smoking has been identified as the major source of indoor particles (particularly fine PM, but also PM10) in smoking households, raising indoor PM concentrations significantly above those in non-smoking 3 households. A PM2.5 concentration of 30 µg/m corresponds to the impact of smoking approximately one pack of cigarettes per day. In non-smoking households, outdoor air is the major source of indoor PM levels. Other indoor sources of particles include such things as wood burning and kerosene stoves and heaters, animal dander, home care and personal care products and various indoor sources of mineral fibres. In general, large home-to-home variations in indoor particle concentrations can be expected. Some studies have reported mean indoor concentrations greater than outdoor levels, while others conclude just the opposite. In many cases, the range of particle concentrations indoors and outdoors is similar. However, in areas where outdoor levels are fairly high, indoor concentrations may well be less, whereas indoor concentrations may greatly exceed outdoor concentrations in areas where outdoor levels are relatively low. Correlations between ambient PM data obtained from fixed ambient monitors (FAMs) and personal exposure data obtained from PEMs have been explicitly examined in many studies.

[top] [end]How to measure smoke levels

Measurements of particulate matter for the purpose of current compliance monitoring are generally expressed in terms of mass. Mass measurements may be made directly or indirectly. Direct (or manual) measurements of PM concentrations in the ambient air are made by collecting particles on a pre-weighed filter over a specified period of time, weighing the soiled filter, and then dividing the gain in mass by the volume of air sampled. Samples are typically collected for a 24-hour period Different sampling periods and frequencies may be used where required, although the fact that the filters are collected manually is a constraint on the operation of these samplers. Indirect measurements are made using parameters other than mass that can then be converted to units of mass concentration based on known relationships between the two parameters. The comparability of PM mass measurements made with different samplers is an issue of concern. Differences may arise from cut point biases, differences in maintenance regimes that in turn affect operation of the instrument and other factors.

A variety of analytical techniques are available for determining concentrations of inorganic and organic compounds from mass filter specimens of particulate matter. Some of these are non-destructible methodologies that leave the filter intact, enabling further chemical analyses; others are destructive of the filter.

Indirect measurements of particulate matter have historically been made using two methodologies: the British Smoke Shade (BSS) sampler and the AISI sampler, which measures Coefficient of Haze (CoH). Both the BSS and the CoH techniques are based on optical properties of particles and are most sensitive to the sooty components of PM that fall in the size range of approximately -3.5-4.5 µm in diameter. The Beta Attenuation monitor, also known as the beta-gauge monitor, has been used in Europe and Japan for several years. Mass determination is based on the attenuation that a beta-ray particle undergoes as it passes through an exposed filter. The beta attenuation monitor can provide hourly PM concentrations, but is a very expensive instrument and has a number of operational constraints.

In contrast to the techniques described above, development of the Tapered Element Oscillation Microbalance (TEOM) offers the opportunity for much less labour intensive continuous measurement of PM concentrations; The TEOM sampler operates 24 hours a day and is automated. The TEOM operates on the principle that PM accumulations on a filter will result in changes to the oscillation frequency of a specially designed tube attached to the filter. Based upon the direct relationship between PM mass and oscillation frequency, the instrument's microprocessor computes the total mass accumulation on the filter, as well as the mass concentrations and mass rate, in real time. TEOM samplers can be fitted with either a PM10 or PM2.5 sampling inlet, but not both at once. As with manual samplers, issues of comparability of measurements have arisen.

[top] [end]Spatial Representativeness

In developing a monitoring network, selection of monitoring sites must be based on siting criteria that reflect the purpose of the data collection exercise and that will minimize undue bias in the resulting measurements. Nonetheless, individual sites are unique with respect to sensor location, surrounding structures, land use patterns, local meteorology etc. all of which will influence ambient pollution levels. As a result, it is recognized that monitoring data from fixed samplers may not portray pollution levels representative of the entire community. Furthermore, fixed monitors do not accurately reflect pollution levels that individuals may be exposed to (see section below on Human Exposure Assessment). To better characterize individual exposures, Personal Exposure Monitors (PEMS), sampling devices worn on the body, have been developed. Due to the nature of their application, however, the design of PEMS must meet a number of challenging criteria: low noise, light weight, portability, rugged design, ease of operation, adequate battery lifetime to meet sampling requirements and comparability with fixed site monitors.

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Page created: 21 August 2003; Last edited: 20 August 2007; Version: 8
Knowledge Bank text is available under the terms of the GNU Free Documentation License.

Pagename: Smoke @HEDON: UBAA