Temporal coverage: 9 May 2013 - present
The Microwave Limb Sounder (MLS) Sulfur Dioxide (SO2) Mixing Ratio layer at 147hPa (hectopascals) indicates sulfur dioxide levels at the vertical atmospheric pressure level of 147hPa, and is measured in parts per billion by volume (ppbv).
Sulfur Dioxide (SO2), a colorless gas with a pungent, suffocating odor, is a very water soluble, acidic gas. SO2 is one of the US Environmental Protection Agency's (EPA) six major regulated criteria pollutants (Tropospheric Ozone, Nitrogen dioxide, Sulfur dioxide, Lead, PM2.5 and PM 10 particulates). It irritates the eyes, nose, and lungs. High concentrations of SO2 can result in temporary breathing impairment. It is produced by combustion of coal, fuel oil, and gasoline, since these fuels contain sulfur in the combustion, and in the oxidation of naturally occurring sulfur gases. It is a precursor to sulfuric acid, which is a major constituent of acid rain. SO2 is injected into the stratosphere by volcanic eruptions. SO2 also is a major precursor to PM2.5 (Particulate Matter up to 2.5 micrometers in size), which is a significant health concern, and a main contributor to poor visibility.
MLS can measure SO2 injected into the upper troposphere and lower stratosphere by explosive volcanoes. Starting with its reaction with OH, SO2 is converted into sulfate aerosol which can impact climate.
The MLS Sulfur Dioxide (SO2) Mixing Ratio 147hPa layer is derived from the MLS Sulfur Dioxide product (ML2SO2_NRT) available from the Microwave Limb Sounder (MLS) instrument on the Aura satellite. The sensor resolution is 5 km, imagery resolution is 2 km, and the temporal resolution is twice daily (day and night).
References: GES DISC - ML2SO2_NRT: MLS/Aura Near-Real-Time L2 Sulfur Dioxide (SO2) Mixing Ratio V004; MLS - SO2 Product; GES DISC - Sulfur Dioxide