Ozone in air

Ozone occurs in the upper atmosphere, where it serves a useful purpose in protecting us from UV radiation. Ozone can also occur near the ground where we breathe. Ozone is very reactive, affecting the linings of the throat and lungs, restricting the air passages and making breathing difficult. It also increases the risk of respiratory infections. Ozone is of greater concern for the elderly and those with existing lung disease.

Sources of ozone

Ozone is the main active element in summer smog, which forms around cities on sunny days with light winds. Ozone is formed in air by reactions between hydrocarbons and oxides of nitrogen. Some hours of strong sunlight are required for high levels of ozone to form.

Sources of the emissions from which ozone is formed are widespread and include automobiles, industry, power stations, bushfire smoke, and commercial and domestic activities.

Current standards for ozone

The current one-hour and four-hour standard levels for ozone are 0.10 ppm (parts per million) and 0.08 ppm respectively.

Goal for ozone

The one-hour and four-hour ozone standards should not be exceeded on more than one day per year.

How much ozone do we detect in Victoria?

In recent years levels have remained below the standards except when bushfire emissions have caused ozone peaks.

Ozone air quality categories

The ozone (O3) data on our website will be shown in different colours, depending on the amount of O3 in the air. The categories range from green – when levels of O3 are low and air quality is very good – through to black – when high levels of O3 result in very poor air quality.

Air quality category O3 ppb
Very good 0–26
Good 27–52
Fair 53–79
Poor 80–119
Very poor 120 or greater

Page last updated on 7 Feb 2019