Airborne Pollutant Overview
Sulphur Dioxide (SO2)
What is Sulphur Dioxide?
Sulphur dioxide (SO2) is a colourless gas belonging to the family of
gases called sulphur oxides (SOx). SO2 smells like burnt matches.
Natural sources of sulphur dioxide include releases from volcanoes,
oceans, biological decay, and forest fires. The most important
man-made sources of sulphur dioxide are fossil fuel combustion,
smelting, manufacture of sulphuric acid, conversion of wood pulp to
paper, incineration of refuse, and production of elemental sulphur.
Coal burning is the single largest man-made source of sulphur dioxide.
How do we measure SO2?
Using U.V FLUORESCENCE: Absorption of ultraviolet radiation by SO2
sulphur dioxide is followed by fluorescence at higher wavelengths.
Ambient air is drawn through a cell where it is irradiated with
ultraviolet light. The resulting fluorescence is detected by a
photomultiplier tube. The amount of fluorescence is a measure of the
sulphur dioxide concentration. SO2 is measured continuously at the air
monitoring stations.
Ambient Air Quality Criteria (AAQC)
Defined as a concentration of a contaminant in ambient air that is protective against adverse effects on health and/or the environment.
- MECP: 10-minute AAQC: 67 ppb (parts per billion) or 178 µg/m³
- MECP: 1-hour AAQC: 40 ppb or 106 µg/m³
- MECP: Annual AAQC: 4 ppb or 11 µg/m³
Health Effects of Sulphur Dioxide
SO2 is an irritant. Inhalation of SO2 can lead to symptoms that include burning of the nose and throat, breathing difficulties, respiratory illness, and aggravation of pre-existing respiratory conditions, such as bronchitis, emphysema, lung or heart disease. Exposure to high concentrations of SO2 can lead to bronchospasms, pulmonary edema (fluid accumulation), pneumonitis (lung inflammation), and acute airway obstruction. Population studies indicate that short-term exposure to high levels of SO2 can lead to respiratory illness, emergency room visits and/or hospitalizations. The risk of health effects from exposure to SO2 is dependent on several factors including concentration, duration & frequency of exposure as well as underlying vulnerability of exposed individual. For example, persons with pre-existing respiratory disease, asthmatics and people with heart disease being especially vulnerable to SO2 effects.
| Category |
Sulphur Dioxide Concentration
(1-hr Average) |
Adverse Health Effects |
| Good |
0 - 40 parts per billion |
No adverse health effects expected. |
| Moderate |
41 - 120 parts per billion |
Asthmatics may experience reduction of lung function but no perceptible
effects on breathing. No need to modify your usual outdoor activity
unless you experience symptoms such as coughing or throat irritation.
|
| Poor |
121 - 250 parts per billion |
Unhealthy for sensitive groups (people with asthma, children and older
adults). Asthmatics may experience measurable effects on lung function
and perceptible effects on breathing. People with asthma should
consider limiting outdoor exertion.
|
| Very Poor |
>250 parts per billion |
Asthmatics are likely to experience reduction of lung function,
perceptible effects on breathing and may require medical intervention.
The general population, and especially children, people with asthma,
older adults or those with lung disease, should limit outdoor
exertion.
|
Oxides of Nitrogen (NOx)
What are Oxides of Nitrogen?
Oxides of Nitrogen (NOx) include the gases nitrogen oxide (NO) and
nitrogen dioxide (NO2). NOx is formed primarily from nitrogen
contained in fuel and nitrogen contained in combustion air during
combustion processes. NO emitted during combustion quickly oxidizes to
NO2 in the atmosphere.
How do we measure NOx?
The analyser uses the principle of chemiluminescence detection. When
NO and Ozone react, they produce a characteristic luminescence with an
intensity proportional to the NO concentration. NO2 must first be
converted into NO before it can be measured using the
chemiluminescence detection method. This is done using a
high-temperature (325 degrees C) NO2 to NO converter. The analyser
continuously measures and records NO, NO2, and NOx readings.
Ambient Air Quality Criteria (AAQC)
Defined as a concentration of a contaminant in ambient air that is protective against adverse effects on health and/or the environment.
- MECP: 1-hour NO2 AAQC: 200 ppb or 400 µg/m³
- MECP: 24-hour AAQC: 100 ppb or 200 µg/m³
Health Effects of Nitrogen Oxides
Nitrogen oxides (NOx) are defined as the sum of Nitrogen Doxide (NO2) and Nitric Oxide (NO). In ambient air NO rapidly converts to NO2. NO2 has adverse health effects at much lower concentrations than NO. Evidence from controlled human exposure studies supports a causal relationship between short-term exposure to elevated NO2 levels and respiratory effects characterized by decreased lung function, increased airway hyperresponsiveness and airway inflammation. Individuals with certain pre-existing diseases such as asthmatics and especially asthmatic children, persons with allergies, with chronic obstructive pulmonary disease and older adults appear to be especially vulnerable. Even short-term exposures to elevated levels of NO2 can lead to exacerbation of asthma symptoms with increases in airway responsiveness.
