Explanation of Aerosol Sampling Terms

This page explains the terms and units used when studying fine particle pollution.


All numbers given are for 2.5 μm diameter or less particles (PM2.5) and are measured in nanograms per cubic metre of air sampled (ng/m3), where 1ng equals one thousand-millionth of a gram and 1,000 ng = 1 µg, one microgram.
All percentages are expressed as a percentage of the measured total fine particulate mass. 
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This corresponds to the mean total weight of particulate matter, of diameter less than 2.5 µm, in the air for a corresponding 24 hour average during the month. The World Health Organisation (WHO) has a goal of 40,000 ng/m3 for less than 10 µm diameter particles (PM10).

The US EPA recommends a PM2.5 goal of 15 µg/m3 for an annual average and 35µg/m3 for a maximum 24 hour average. Currently there is no such NSW standard for PM2.5 particulates. However, the Australian National Environment Protection Council (NEPC) proposed a PM2.5 goal of 8 µg/m3 annual average and 25 µg/m3 for 24 hour average for Australia in 2005.

Ammonium Sulfate, (NH4)2SO4

This is an estimate of the amount of particulate ammonium sulphate [(NH4)2SO4] that is contained within a sample and it is obtained from the measurement of sulphur. Ammonium sulphate originates from the conversion of sulphur dioxide gas (SO2), from coal burning, industry and motor vehicles, to sulphuric acid (H2SO4), which is then neutralised by ammonia present in the atmosphere. The 'Acid Rain' problem arises when there is incomplete neutralisation of this acidic aerosol.

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Organic Matter 


Organic matter is an estimate of any organic compound detected, Organics are those compounds generally containing carbon (C), hydrogen (H) and oxygen (O). In our case it is estimated through measurements of the hydrogen content with the removal of hydrogen associated with ammonium compounds.

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The fine particle soil concentration (PM2.5) is found from the summation of the different oxides found in soil such as silicon oxide (SiO2), aluminium oxide (Al2O3), iron oxides (FeO, Fe2O3), calcium oxide (CaO), and titanium oxide (TiO2).


Soil in the atmosphere occurs from natural wind blown dust, agriculture and industries such as quarrying.

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Elemental Carbon


The visual degradation of an urban atmosphere is strongly influenced by the presence of elemental, black or sooty carbon. The elemental carbon concentration gives an indication of the amount of soot that is present and is obtained by a laser absorption technique on filter before and after exposure.


It is mainly produced by motor vehicles and biomass burning. Our estimates assume a mass attentuation coefficient of 7 m2/g.

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Sea Salt


In general sea salt is only a significant factor in marine environments, though its inclusion can show the seasonal variations in wind direction for coastal or near coastal localities.


It is estimated from the measurement of sodium.

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Potassium (K) Iron (Fe), Zinc (Zn), Lead (Pb)


The remaining four columns contain representative trace elements with particular source significance such as biomass or wood burning (potassium, K), industry and incineration (iron, Fe, zinc, Zn and lead, Pb) and automobiles (zinc, Zn and lead, Pb).

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