SO₂ data and alert service

Introduction

Slant column density vs. vertical column density

Geographic regions

Data presentation and delivery

Solar Zenith Angle

What is the Dobson Unit?

Slant column retrieval

Background correction

Reference spectrum

Cloud cover fraction

Near-real time service

Criteria for exceptional SO2 concentrations

Air-mass factor using look-up tables

Air-mass factor using a chemistry transport model

SO2 column from OMI

Time period of available data

Data format specification

Data and Service version history

Validation of the data products

South Atlantic Anomaly

Downloading data & image files

Documentation

References

Acronyms

Acknowledgments

Introduction

Changes in the abundance of SO2 have an impact on atmospheric chemistry and hence on air quality and on climate. Effects of volcanic eruptions may have an impact on air traffic, as such eruptions are important sources of ash (aerosols) and SO2. Consequently, global observations of SO2 are important for atmospheric and climate research, and for air traffic organisations. Global monitoring of SO2 concentrations is done on the basis of UV-Visible measurements by satellite based nadir-viewing instruments.

Volcanic emissions and strong pollution events are clearly detected with this approach, which makes it very suitable for use in a Near-real time (NRT) service, with an automatic Notification (or: Alert) Service for exceptional SO2 concentrations. In addition to that an off-line (reprocessed) archive of data is useful for validation of the Service and the data, and for case studies of past events.

The SO2 Services described here are closely linked to the so-called Support to Aviation Control Service (SACS) of the PROMOTE project. Apart from the SO2 data, SACS also intends to deliver a volcanic ash indicator (VAI) as well as backward and forward trajectories from the location of an SO2 peak value in case of an SO2 alert. The trajectories are meant to indicate the possible origin and future motion of the SO2, and the VAI is meant to provide additional information on possible volcanic eruptions.

The on-line product information

Currently in use are SCIAMACHY (aboard ENVISAT) and OMI (aboard EOS-Aura). Later will follow data based on GOME-2 (aboard MetOp). Also a reprocessing of old GOME-1 (aboard ERS-2) data for the archive is planned.

The Services are set up using data from SCIAMACHY and so the product information is written from that starting point. Most information is, however, valid for the data of all instruments used -- if this is not the case, it is mentioned explicitly.

A printable version of this on-line documentation
can be found in the documentation section.

SO2 data products

The SO2 column archive service provides global maps (monthly, 3-day composite [SCIAMACHY only] and daily) and global orbit data files. Higher resolution maps over pre-defined regions covering areas of possible volcanic and anthropogenic sources of SO2 are provided as well. In addition access to the data files is given.

The near-real time service provides maps of daily orbit data files only, as well as the orbit data files themselves (except for OMI, for which only maps are presented).
 

Other data products

The foreward and backward trajectories will be added and described in due time.