The plot shows the location of the SO₂ notifications of the selected month, or to be more precise:
it shows the location of the centre of the segment that triggered the notification. Coloured circles
are used to symbolise different cases:

• Notifications indicated by red circles, with small (large) circles for low (high) SO₂
  concentrations (VCD, given in Dobson Units), are in most cases probably real (either
  related to volcanic or to anthropogenic activity). The higher the solar zenith
  angle (SZA), however, the more difficult the SO₂ retrieval is, and SO₂ concentrations
  for SZA > 70 degrees or so are suspect.

• Notifications related to measurements taken over the geographic area known as the South
  Atlantic Anomaly (SAA) are indicated by yellow circles for all SZA. These notifications are
  in most cases false, although they could be related to activity of volcanoes along
  the west coast of South America.

• Notifications related to measurements taken at really high SZA, i.e. at low Sun, and outside
  the SAA are indicated by blue circles. These notifications are most likely false, unless
  a volcanic cloud with high SO₂ concentrations is moving at high latitudes.

Notifications issued by email are limited to SZA <= 80 degrees. Data in the plots (maps) was
limited to SZA <= 85 degrees up to July 2009; after that the plots are limited to SZA <= 80 degrees (data files have data for SZA <= 85 degrees).

Numbers of notifications in the different categories are listed in the table close
(as of August 2009 the 'SZA > 80' column should be zero).