Air quality
Definitions & abbreviations

The percentage time for which a monitoring instrument has produced valid data.

Some instruments measure averages of particle concentrations for each whole day. If we monitor for a whole year, then the data recovery is the percentage of days out of 365, when we have valid or good quality data. If we monitor for a shorter period, say six months, then data recovery is the percentage of 180 days where the data is of good quality.

Some other instruments provide average readings for every hour of every day. For example a NO_x monitor could provide up to 8,760 hourly average readings per year. However, this is not normally possible. An hour or so is lost each day because of routine automatic calibration; and regular maintenance will also reduce the number of valid hourly average readings.

So an instrument is rarely able to produce good data 100% of the time. Inevitably, instrument problems and breakdowns will occur during the year, which again reduce the data recovery rate.

In practice EPA aims to maintain its data recovery to better than 90%.

Environment Protection and Heritage Council, established under COAG.

The EPHC has now been superseded by SCEW [see SCEW].

High volume sampler, an instrument used for collecting samples of particles from the air. It is a little like a large vacuum cleaner that pulls air through a special filter, so that any dust or smoke can be weighed or tested for different chemicals.

The EPA uses high volume samplers to collect samples of particles that are then used to determine the concentration of lead in air [see also Pb].

A particle is a tiny piece of a something that is solid or liquid. Particles can be soil, rock, or mineral dust; or may be a very complicated mixture of many different chemicals, like smoke or vehicle exhaust.

The smallest ones may be suspended in the air. For example, water droplets in fog are a type of particle suspended in the air. A collection of particles is sometimes called PM or particulate matter.

Particle size is important because it determines whether particles will be trapped in our noses and throats or whether they can enter our lungs, where they may cause damage. Particles come in many different sizes and shapes: round and smooth, long and thin, or rough and irregular. 

However, what really matters is whether we can breathe them in. So air pollution monitors are designed to sample air in the same way as we breathe air into our lungs, whatever shape they may have. Scientists measure all particles as if the behave like tiny round droplets of water. When we describe particles as having a size of 10 millionths of a metre (10 mm), we mean that they can enter our lungs when we breathe, as if they are droplets of water 10 millionths of a metre in diameter.

This is often called equivalent aerodynamic diameter or EAD for short.

The pages on the EPA website and most reports simply use particle size instead of EAD.

lead. Lead is most commonly measured in total suspended particulates using high volume samplers [see TSP].

The EPA currently monitors lead concentrations in air in Port Pirie.

PM₁₀ is a name given to particles in the air that are small enough for us to be able to breathe them in. Some of the larger ones may only reach as far as our throats, while others may travel right down into our lungs.

PM means particulate matter, while the '10' tells us how big the particles are, in micrometres or millionths of a metre. This is written as 10 µm. PM₁₀ means that the biggest particles in a sample are about 10 µm in diameter.

A sample of PM₁₀ particles may also contain PM_2.5 particles [see PM_2.5].

PM_2.5 is a name given to particles in the air that are so small that when we breathe them in, they can travel right down into the deep parts of our lungs.  PM_2.5 means that the largest particles have sizes of around 2.5 micrometres or µm [see explanation of µm under PM₁₀].

Common types of PM_2.5 particles are smoke and exhaust fumes from vehicles.

parts per billion (by volume).  This is a way of measuring very small concentrations of gases in the air.

For example: one part-per-billion of carbon monoxide (CO) is like adding 1 microlitre (µL) of pure CO gas to a cubic metre of air (m³).

To convert from ppb to ppm: divide the ppb concentration by 1000 and this gives the concentration in ppm.

parts per million (by volume). This is a way of measuring very small concentrations of gases in the air. 

For example: one part-per-million of carbon monoxide (CO) is like adding 1 millilitre (mL) of pure CO gas to a cubic metre of air (m³).

For some pollutants, we have standards that are set for averages longer than one hour.  Some may be 4 hours or even 8 hours. How do we choose the best eight hour periods within a day to calculate these averages?

There are 2 ways of calculating 8-hour averages in each day

• We could calculate an 8-hour average from midnight to 8 am; then calculate the average from 8 am to 4 pm; then 4 pm to midnight. This gives us three averages for each day.
• Another way is to calculate the eight-hour average concentration from midnight to 8 am; then calculate the average from 1 am to 9 am; then 2 am to 10 am; 3 am to 11 am; all the way up to midnight again. This is called a rolling average and is often used for air quality monitoring. It seems complicated, but it can give us better information to compare pollution concentrations with national standards.

total suspended particulates. TSP is a name given to particles of sizes up to about 50 µm.  The larger particles in this class are too big to get past our noses or throats, so they cannot enter our lungs.  They are often from wind blown dust and may cause soiling of buildings and clothes. However, TSP samples may also contain the small PM₁₀ and PM_2.5 particles that may enter our lungs [see explanation under PM₁₀ and PM_2.5].

TSP are generally measured by HVS [see HVS].

Validation is a standard procedure for checking data is accurate and either correcting or removing data that is incorrect. Examples of why data may be incorrect are that the instruments have not worked properly or there has been a power failure.

The resulting data set where incorrect data has been corrected or removed is called valid data. This data is then used by the EPA to report on air quality.

Data used for the Air Quality Index comes straight from the monitoring instruments and has not been through this process.