All Houston monitors meet current health-based standards.
Sulfur dioxide (SO2) is one of a group of highly reactive gasses known as “oxides of sulfur.” The largest sources of SO2 emissions are from fossil fuel combustion at power plants (73%) and other industrial facilities (20%). Smaller sources of SO2 emissions include industrial processes such as extracting metal from ore, and the burning of high sulfur containing fuels by locomotives, large ships, and non-road equipment. SO2 is linked with a number of adverse effects on the respiratory system.
SO2 is also a contributor to fine particle pollution, and to acid rain, which can cause damage to trees and other vegetation and cause lakes to become more acidic.
In 2010, EPA revised the health-based SO2 standard by establishing a new 1-hour standard at a level of 75 parts per billion (ppb).
Everywhere in the country has air quality that meets the current SO2 standard. Annual average SO2 concentrations, as measured by monitors around the nation, have decreased by more than 70% since 1980. Measurements of the acidity of rain and lakes have also shown decreases.
Houston SO2 Levels 2012