The main sources of air pollution in Mauritius are from the burning of fossil fuel for heat generation in industries, electricity generation and transportation.
The sources of air pollution can be grouped into three categories as follows:
• stationary sources such as power stations and industries (e.g. stone crushing plants);
• mobile sources such as motor vehicles; and
• others such as open burning of waste materials and burning of sugar-cane fields.
2. What are the main air pollutants emitted into the environment?
The following measures are adopted by the MoE in controlling air pollution :
• minimising emissions at source; and
• minimising the impact of residual pollution on surrounding developments by proper siting of industries
• monitoring of ambient air at suspected sites
4. How does the MoE monitor ambient air quality?
The Ministry of Environment has got two ambient air quality monitoring station. The National Environmental Laboratory of the Department of Environment is responsible for the ambient air monitoring. One fixed is at Medco Cassis where regular monitoring is being undertaken. The mobile station is regularly displaced to sites where high pollution levels are suspected. The automatic analysers and equipment at the stations measure the concentrations of major pollutants such as sulphur dioxide, oxides of nitrogen, carbon monoxide, ozone, particulate lead and respirable suspended particles (PM10).
In Mauritius, air pollution control is regulated under the Environment Protection (Standards for Air) Regulations 1998.
The following measures are adopted in Mauritius for controlling water pollution:-
• providing sewerage infrastructure and solid waste management system to prevent pollution at source;
• requiring industries to pre-treat their effluent to prescribed standards before discharge into the sewerage system; and
• prohibiting industries which use or store large quantities of chemicals to be sited within water catchments.
The National Environmental Laboratory of the Department of Environment in collaboration with other laboratories (Ministry of Fisheries, Waste Water Management Authority, Central Water Authority) perform regular monitoring of inland and coastal water quality around the island.
Noise or sound is measured in decibels, dB. The basic instrument used for the measuring of noise is the sound level meter. This instrument is designed to respond in approximately the same way as the human ear and gives objective assessment of sound pressure level.
2. What are the noise exposure limits in Mauritius?
07 00---21 00 hrs --- 60 dB
21 00---0700 hrs --- 55 dB
07 00---18 00 hrs --- 60 dB
18 00---21 00 hrs --- 55 dB
21 00---07 00 hrs --- 50 dB
Power Station Noise
In residential area –
07 00---21 00 hrs --- 60dB
21 00---07 00 hrs --- 55dB
In any other area
At any time --- 70dB
The atmosphere has an abundance of oxygen (O2) which is essential to all earth's living things. Under certain circumstances, three oxygen atoms bond together to form a colourless gas known as ozone (O3).
2. How is ozone formed?
Ozone is formed through a series of photochemical reactions. In the stratosphere, when a molecule of O2 is bombarded by ultraviolet rays, it splits into two free oxygen atoms. Each of these free atoms can then react with another oxygen molecule to form a molecule of ozone (O3). Ozone is sometimes broken up simply by colliding with a free oxygen atom to form two oxygen molecules. Ozone can also react with a variety of oxygen compounds and be transformed back into oxygen. Before humans began polluting the atmosphere, a delicate cycle consists of a well-balanced amount of ozone and oxygen in the atmosphere.
3. Why is the ozone layer under threat?
When released into the air, some man-made chemicals containing chlorine and bromine eventually migrate into higher regions of the atmosphere, including the stratosphere. Though these chemicals are stable in the lower atmosphere, they are broken down into highly reactive forms of chlorine and bromine in the stratosphere by the high levels of UV solar radiation. These chemicals then take part in a series of chain reactions leading to ozone depletion as shown below:-
4. What are the chemicals that destroy the ozone layer?
Chlorofluorocarbons (CFCs), the most widely-known ozone-depleting chemicals were first synthesised in 1928. Because of their inflammability and low toxicity, they were used in applications as diverse as refrigerants in refrigerators and air-conditioners, propellants in aerosol spray cans, blowing agents in the manufacture of foams, and cleaning agents for electronic equipment.
Hydrochlorofluorocarbons (HCFCs), were developed as substitutes for CFC refrigerants and blowing agents. Though less destructive than CFCs, the ozone-depleting potential (ODP) of these chemicals are too high to allow long-term use. (ODP is a measure of a substance ability to destroy stratospheric ozone. It depends on the substance atmospheric lifetime, stability, reactivity and the ozone-depleting elements it contains such as chlorine and bromine. All ODP values are expressed in relation to the baseline value of 1 for CFC-11.)
Two other chlorine containing chemicals, widely used as solvents for cleaning metals, have significant ODP. These are carbon tetrachloride and methyl chloroform.
The main bromine-containing chemicals that destroy ozone are called halons. These are used in fore-extinguishing equipment. Some halons have an ODP ten times higher than that of the most potent CFCs.
Another chemical with a high ODP is methyl bromide, mainly used as an agricultural pesticide and to fumigate agricultural commodities.
These chemicals are collectively known as ozone-depleting substances (ODS). They can be identified by their trade names (e.g. FREON), refrigerant codes (e.g. CFC-113 or R-12) and by their chemical names (e.g. 1,1,1-trichlorotriflouroethane).
The ozone layer shields all life-form from the harmful effects of UV-B radiation by absorbing all but a small fraction of the harmful ultraviolet radiation (UV-B) emanating from the sun. Exposures to high levels of UV-B radiation is extremely dangerous and can cause the following :-
• Skin cancers
• Damage to eyes
• Crop damage
• Severe disruption of the marine ecosystems
• Degradation of man-made materials like paints and plastics
• Increased global warming and climate change