Version 4 is the current version of the data set. Older versions are no longer available and have been superseded by Version 4. These data are a part of MEaSUREs 2012 projects. The particular project, "Multi-Decadal Sulfur Dioxide Climatology from Satellite Instruments", is expected to produce SO2 Earth Science Data Record by means of combining measurements from backscatter Ultraviolet (BUV), thermal infrared (IR) and microwave (MLS) instruments on multiple satellites. The data represent best estimates of the volcanic and anthropogenic contribution to global atmospheric SO2 concentrations. Since SO2 is the major precursor of sulfate aerosol, which has climate and air quality impact, SO2 measurements will contribute to better understanding of the sulfate aerosol distributions and its atmospheric impact." The released data file is a long-term database of volcanic SO2 emission derived from ultraviolet satellite measurements from October 31, 1978, to present. Data are in a table format in simple ASCII format: Column Descriptions: Column 1 = Name of volcano. Column 2 = Latitude of volcano. Column 3 = Longitude of volcano. Column 4 = Altitude of volcano (km). Column 5 = Eruption year. Column 6 = Eruption month of year. Column 7 = Eruption day of month. Column 8 = Eruption style: exp = explosive, eff = effusive. Column 9 = Eruption volcanic explosivity index (nd = no data or undetermined). Column 10 = Observed plume altitude (km) where known. Column 11 = Estimated plume altitude (km) above vent: 10 km for explosive, 5 km for effusive. Column 12 = Measured SO2 mass in kilotons (= 1000 metric tons).