History of Sulfates Air Quality Standard

This page reviewed November 24, 2009.

What are Sulfates?
Sulfates (SO42-) are the fully oxidized ionic form of sulfur. Sulfates occur in combination with metal and / or hydrogen ions. In California, emissions of sulfur compounds occur primarily from the combustion of petroleum-derived fuels (e.g., gasoline and diesel fuel) that contain sulfur. This sulfur is oxidized to sulfur dioxide (SO2) during the combustion process and subsequently converted to sulfate compounds in the atmosphere. The conversion of SO2 to sulfates takes place comparatively rapidly and completely in urban areas of California due to regional meteorological features.
Health and Welfare Effects from Exposure to Ambient Levels of Sulfates
The ARB's sulfates standard is designed to prevent aggravation of respiratory symptoms. Effects of sulfate exposure at levels above the standard include a decrease in ventilatory function, aggravation of asthmatic symptoms, and an increased risk of cardio-pulmonary disease. Sulfates are particularly effective in degrading visibility, and, due to fact that they are usually acidic, can harm ecosystems and damage materials and property.
History of Sulfates Air Quality Standard
  • In 1976, the ARB adopted a sulfates standard at 25 g/m3 for a 24-hour averaging period.

  • This standard was reviewed and retained in 1977 and again in 2002.

For more information on Ambient Air Quality Standards please contact Linda Smith at (916) 327-8225 or email at lsmith@arb.ca.gov.

Ambient Air Quality Standards