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Index Banded Annual Totals for Swansea:
LOW
58 days
MODERATE
39 days
HIGH
10 days
VERY HIGH
8 days

Frequently asked questions

When viewing a daily chart for a gas pollutant the values around midnight are always zero

The data that is uploaded to the website consists of "raw" but edited 15-minute data.

Every night at between 00:30 and 01:00 every gas analyser carries out an automatic calibration. This calibration data is removed automatically from the data uploaded to the website (but held within the databases for QA/QC purposes) and replaced with a zero for each 15-minute datapoint. It is these zero data points that are plotted on the 24-hour daily chart. The daily chart is comprised wholy from 15-minute data.

Please be aware that if the chart time-frame extends over two or more days, the data presented within the chart is in the form of hourly averages and the calibration datapoints are not therefore easily seen. 

Pollution glossary: