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Air Pollution & Health

Air Pollution Index (API)

api.jpg (22922 bytes)Our air pollution problems are related mainly to long-term health effects caused by persistently high levels of tiny particles that can penetrate deep into our lungs. However, our air pollution levels sometimes can become so high that they may have more immediate impacts for those with existing heart or respiratory illnesses. In order to give public a clean and simple picture of the air quality around us, the Hong Kong Environmental Protection Department (EPD) designed a simple way of indicating air quality, namely Air Pollution Index (API).

The API is a simple way of describing air pollution levels to provide timely information about air pollution to the public and to enhance awareness. Since June 1995, the EPD has been reporting the API and making a forecast for the following day. Similar systems are widely used in many other places such as the United States, Singapore, Malaysia, Taiwan and the Philippines.

The API forecast serves as an alert to the public before the onset of serious air pollution episodes. It helps the general public, especially susceptible groups such as those with heart or respiratory illnesses, to consider taking precautionary measures when necessary.

The API ranges from 0 to 500 and is divided into 5 bands according to the potential effects on health. An API number of 100 is particularly important since it indicate to the short-term air quality in Hong Kong. An API higher than 100 means that one or more pollutants may pose immediate health effects to some susceptible members of our community.

The potential health effects for different ranges of API values are as follows:
Air Pollution Level API Health Implication
Severe 201 to 500 People with existing heart or respiratory illnesses may experience significant aggravation of their symptoms and there may be also widespread symptoms in the healthy population. These include eye irritation, wheezing, coughing, phlegm and sore
Very High 101 to 200 People with existing heart or respiratory illnesses may notice mild aggravation of their health conditions. Generally healthy individuals may also notice some discomfort.
High 51 to 100 Very few people, if any, may notice immediate health effects. Long-term effects may, however, be observed if you are exposed to such levels for a long time.
Medium 26 to 50 None expected for the general population.
Low 0 to 25 None expected.

The suggested precautionary actions are summarised below:
Air Pollution Level API Advice to You
Severe 201 to 500 The general public are advised to reduce physical exertion and outdoor activities
Very High 101 to 200 Persons with existing heart or respiratory illnesses (such as coronary heart and cardiovascular diseases, asthma, chronic bronchitis and chronic obstructive airways diseases) are advised to reduce physical exertion and outdoor activities
High 51 to 100 No immediate response action is suggested -- Long-term effects may, however, be observed if exposed at this level persistently for months or years
Medium 26 to 50 No response action is required.
Low 0 to 25 No response action is required.

You can visit EPD's website for more details (www.epd.gov.hk)

Typical Air Pollutants around You

airpollutants.jpg (23223 bytes)The air we breathe can be contaminated with pollutants from factories, vehicles, power plants, and many other sources. These pollutants have long been a major concern because of the harmful effects they sometimes have on people's health and the environment. Their impact depends on many factors, including the quantity of air pollution to which people are exposed, the duration of the exposures, and the potency of the pollutants. The effects of air pollutants can be minor and reversible (such as eye irritation) or debilitating (such as aggravation of asthma) and even fatal (such as cancer).

Air pollutants are those pollutants that are known or suspected to cause cancer or other serious health effects, such as reproductive effects or birth defects, or to cause adverse environmental effects. The degree to which a toxic air pollutant affects a person's health depends on many factors, including the quantity of pollutant the person is exposed to, the duration and frequency of exposures, the toxicity of the chemical, and the person's state of health and susceptibility.

Typical there are six common air pollutants, they are sulphur dioxide (SO2), carbon monoxide (CO), ozone (O3), nitrogen dioxide (NO2), Volatile Organic Compounds (VOCs) and suspended particulate (SP),

Gaseous Pollutants

  • Sulphur Dioxide
  • Carbon Monoxide
  • Nitrogen Dioxide
  • Ground-level Ozone
  • Volatile Organic Compounds (VOCs)

Particulates Pollutants

  • Particulate matter (Total and Respirable Particulates)

Sulphur Dioxide
Sulfur dioxide, or SO2, belongs to the family of sulfur oxide gases (SOx). These gases dissolve easily in water. SOx gases are formed when fuel containing sulfur, such as coal and oil, is burned. SO2 dissolves in water vapor to form acid, and interacts with other gases and particles in the air to form sulfates and other products that can be harmful to people and their environment.

Health and Environmental Impacts
Respiratory Effects from Gaseous SO2 - Peak levels of SO2 in the air can cause temporary breathing difficulty for people with asthma who are active outdoors. Longer-term exposures to high levels of SO2 gas and particles cause respiratory illness and aggravate existing heart disease.

Respiratory Effects from Sulfate Particles - SO2 reacts with other chemicals in the air to form tiny sulfate particles. When these are breathed, they gather in the lungs and are associated with increased respiratory symptoms and disease, difficulty in breathing, and premature death.

Visibility Impairment - Haze occurs when light is scattered or absorbed by particles and gases in the air. Sulfate particles are the major cause of reduced visibility in many parts of the U.S., including our national parks.

Acid Rain - SO2 and nitrogen oxides react with other substances in the air to form acids, which fall to earth as rain, fog, snow, or dry particles. Some may be carried by the wind for hundreds of miles.

Carbon monoxide
Carbon monoxide, or CO, is a colorless, odorless gas that is formed when carbon in fuel is not burned completely. It is a component of motor vehicle exhaust, they are also coming from other non-road engines and vehicles. Higher levels of CO generally occur in areas with heavy traffic congestion and other heavy industrial areas.

Health and Environmental Impacts
Cardiovascular Effects - The health threat from lower levels of CO is most serious for those who suffer from heart disease, like angina, clogged arteries, or congestive heart failure. For a person with heart disease, a single exposure to CO at low levels may cause chest pain and reduce that person's ability to exercise; repeated exposures may contribute to other cardiovascular effects.

Central Nervous System Effects - Even healthy people can be affected by high levels of CO. People who breathe high levels of CO can develop vision problems, reduced ability to work or learn, reduced manual dexterity, and difficulty performing complex tasks. At extremely high levels, CO is poisonous and can cause death.

Smog - CO contributes to the formation of smog ground-level ozone, which can trigger serious respiratory problems.

Nitrogen oxides
Nitrogen oxides, or NOx, is the generic term for a group of highly reactive gases, all of which contain nitrogen and oxygen in varying amounts. Nitrogen oxides form when fuel is burned at high temperatures, as in a combustion process. The primary manmade sources of NOx are motor vehicles, electric utilities, and other industrial, commercial, and residential sources that burn fuels. NOx can also be formed naturally.

Health and Environmental Impacts
Ground-level Ozone (Smog) - is formed when NOx and volatile organic compounds (VOCs) react in the presence of sunlight. Children, people with lung diseases such as asthma, and people who work or exercise outside are susceptible to adverse effects such as damage to lung tissue and reduction in lung function.

Acid Rain - NOx and sulfur dioxide react with other substances in the air to form acids which fall to earth as rain, fog, snow or dry particles. Some may be carried by wind for hundreds of miles. Acid rain damages; causes deterioration of cars, buildings and historical monuments; and causes lakes and streams to become acidic and unsuitable for many fish.

Global Warming - is also a greenhouse gas. It accumulates in the atmosphere with other greenhouse gasses causing a gradual rise in the earth's temperature. This will lead to increased risks to human health, a rise in the sea level, and other adverse changes to plant and animal habitat.

Ground-level Ozone
Ozone (O3) is not usually emitted directly into the air, but at ground level is created by a chemical reaction between oxides of nitrogen (NOx) and volatile organic compounds (VOC) in the presence of sunlight. Motor vehicle exhaust and industrial emissions, gasoline vapors, and chemical solvents as well as natural sources emit NOx and VOC, that help to form ozone. Sunlight and hot weather cause ground-level ozone to form in harmful concentrations in the air.
Health Impacts
Ozone can irritate lung airways and cause inflammation much like a sunburn. Other symptoms include wheezing, coughing, pain when taking a deep breath, and breathing difficulties during exercise or outdoor activities. People with respiratory problems are most vulnerable, but even healthy people that are active outdoors can be affected when ozone levels are high.

Even at very low levels, ground-level ozone triggers a variety of health problems including aggravated asthma, reduced lung capacity, and increased susceptibility to respiratory illnesses like pneumonia and bronchitis.

Volatile Organic Compounds (VOCs)

Volatile organic chemicals (VOCs) are emitted as gases from certain solids or liquids which contain organic compounds. In many household products, VOCs is found to be a common ingredient. Paints, varnishes, and wax all contain organic solvents, as do many cleaning, disinfecting, cosmetic, degreasing, and hobby products. Fuels are made up of organic chemicals. All of these products can release organic compounds while you are using them, and, to some degree, when they are stored. When these organic compound released to atmosphere, they become VOCs and a key contributor of smog formation.

Health Impacts
VOCs can have direct effects on eye, nose, and throat irritation; headaches, loss of coordination, nausea; damage to liver, kidney, and central nervous system. Some organics can cause cancer in animals; some are suspected or known to cause cancer in humans.

The ability of organic chemicals to cause health effects varies greatly from those that are highly toxic, to those with no known health effect. As with other pollutants, the extent and nature of the health effect will depend on many factors including level of exposure and length of time exposed. Eye and respiratory tract irritation, headaches, dizziness, visual disorders, and memory impairment are among the immediate symptoms that some people have experienced soon after exposure to some organics.

Smog is sometimes called photochemical smog or photochemical air pollution. One of smog's key ingredients is formed when volatile organic compounds (VOCs) react with ozone in the presence of sunlight. A simple chemical formula for this reaction would be:

1) O3 + VOC + light --> oxidized organic compounds

The oxidized organic compounds then mix with many other compounds and small particles in the air to create smog:

2) oxidized organic compounds + many other compounds --> photochemical smog

Humans feel the effects of smog most often by experiencing respiratory trouble. Although the exact degree of health effects of smog is unknown, lung function and breathing can certainly be affected. Smog is also hazardous because it decreases visibility.

Particulate matter (Total and Respirable Particulates)

Particulate matter, or PM, is the term for particles found in the air, including dust, dirt, soot, smoke, and liquid droplets. Particles can be suspended in the air for long periods of time. Some particles are large or dark enough to be seen as soot or smoke. Others are so small that individually they can only be detected with an electron microscope.

Some particles are directly emitted into the air. They come from a variety of sources such as cars, trucks, buses, factories, construction sites, tilled fields, unpaved roads, stone crushing, and burning of wood.

The difference between total and respirable particulates is their size. Size of respirable particulates is so small that they can be breathed directly into our lung, but total particulates cover both respirable and non-respirable particulates.

Health Impacts

Many scientific studies have linked breathing PM to a series of significant health problems, including:

  • aggravated asthma
  • increases in respiratory symptoms like coughing and difficult or painful breathing
  • chronic bronchitis
  • decreased lung function
  • premature death

Visibility impairment - PM is the major cause of reduced visibility (haze)


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