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Clear The Air Definitions

Please find below a list of all the technical terms and their definitions used on our website.

API - Air Pollution Index

API measures the amount of the 4 main greenhouses gases (sulphur dioxide, carbon monoxide, ozone and nitrogen dioxide) in a day based on the possible health effects of air pollutants.

Two API's are measured in Hong Kong: General API and Roadside API. Hong Kong is the first city in the World to issue a Roadside Air Pollution Index on a regular basis.

Carbon Monoxide

Carbon Monoxide is a colourless, odourless and tasteless gas.

It is produced by the incomplete burning of car-containing fuels, such as petrol, coal and wood.

It can reduce oxygen delivery to the body's organs and tissues when it enters the bloodstream causing slow responses, fainting and even death.

Nitrogen Dioxide (NO2)

What is Nitrogen Dioxide?

A corrosive light brown gas
In sunlight, nitrogen dioxide can react with compounds in the air to make another hazardous pollutant, ozone (see below)

What can Nitrogen Dioxide do to you?

It can irritate the lungs
It can lower resistance to respiratory diseases such as influenza
People already suffering from respiratory problems, such as asthma, are especially vulnerable
It may impair children's lung development
It can increase the chances of children developing asthma
It may lead to structural changes in the lungs

Where does Nitrogen Dioxide come from?

Power plants
Car exhausts

Ozone

What is Ozone?

Called a secondary pollutant because it is not directly emitted, it is produced by reactions of other pollutants
People are often exposed to ozone pollution in everyday life
Ozone concentrations are especially strong in times of weak wind and bright sunlight.

What can Ozone do to you?

It can cause breathing problems, trigger asthma
It can cause coughing and chest pains, and can irritate the throat and eyes
It can lower resistance to respiratory diseases
It can cause inflammation and malfunction of the lungs
People already suffering from respiratory problems, such as asthma, are especially vulnerable

Where does Ozone come from?

From the photo chemical reaction of other polluting gases (such as nitrogen oxides) with oxygen in sunlight

Particlulate Matter or RSP - Respirable Suspended Particulates

What is Particulate Matter?

Tiny particles suspended in the air
Particles with a diameter less than 10 micrometers are called respiratory suspended particulates (RSP) or PM10.
Those less than 2.5 micrometers in diameter are called PM2.5 and are a major health hazard

What can Particulate Matter do to you?

This is the air pollutant that poses the biggest threat to human health
It can make it difficult to breathe
It can damage lung tissue
It can aggravate existing cardiovascular diseases and lung problems
Some particles may cause cancer
Particles with a diameter of 2.5 micrometers（PM2.5）are able to penetrate deep into the lungs without interception by nose or throat hairs
The elderly and children are especially vulnerable

Where does Particulate Matter come from?

Power plants burning fossil fuels The electrostatic precipitators in the chimney stacks catch 99% of the larger particulates but they cannot catch the fine PM2.5 particulates (thousands of tonnes per year into HK's air) - however there is technology available (called Indigo Agglomerator) to catch the vast majority of these particulates; we just need to compel the HK Government to increase the Air Quality Objectives and include PM2.5 levels to force local power companies to fit the technology.
Diesel vehicle exhausts - old inefficient diesel vehicles need to be forced off our roads
All kinds of atmospheric chemical air pollutants and fine particles suspended in the air such as construction dust, soil, soot, tobacco and cigarette smoke. In California USA, tobacco smoke is classified as a Toxic Air Contaminant, akin to diesel fumes.

Sulphur Dioxide (SO2)

What is Sulphur Dioxide?

A colourless gas
It has a pungent smell at very high concentrations.

What can Sulphur Dioxide do to you?

The latest research shows that even low concentrations of SO2 can be harmful to your health
It can make it difficult to breathe and affect lung functions
It can irritate the eyes
It can aggravate existing respiratory problems
People sensitive to SO2 may develop symptoms such as wheezing, shortness of breath and coughing
Asthmatics and individuals with cardiovascular disease or chronic lung disease (such as bronchitis or emphysema) as well as children and the elderly are especially vulnerable

Where does Sulphur Dioxide come from?

Power plants that burn fossil fuels
Vehicles running on sulphur-containing diesel fuels