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Glossary 

This glossary provides definitions of common terms used in the context of air pollution.

You can navigate quickly to a term using the alphabetic links below; clicking on the terms will show their definition.



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  • Running mean
    This is a mean - or series of means - calculated for overlapping time periods, and is used in the calculation of several of the National Air Quality Standards. For example, an 8-hour running mean is calculated every hour, and averages the values for eight hours. The period of averaging is stepped forward by one hour for each value, so running mean values are given for the periods 00:00 - 07:59, 01:00 - 08:59 etc. This can also be considered as a "moving average". By contrast, a non-overlapping mean is calculated for consecutive time periods. Using the same 8-hour mean example, this would give values for the periods 00:00 - 07:59, 08:00 - 15:59 and so on. There are, therefore, 24 possible 8-hour running means in a day (calculated from hourly data) and 3 non-overlapping means.

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Page last modified: 14 February 2011