Aug 29 (Reuters) - The U.S. Environmental Protection Agency (EPA) has issued an emergency waiver in El Paso County, Texas of rules governing gasoline vapor pressure linked to ozone pollution, or smog, due to a fuel supply emergency caused by unplanned outages at two refineries.

The waiver will be effective from Aug. 28 to Sep. 16, EPA said.

The Texas Commission on Environmental Quality (TCEQ) requested the waiver on Aug. 26 on behalf of Texas Governor Greg Abbott. The regulation being waived requires gasoline sold in the El Paso area to have a Reid Vapor Pressure (RVP) of 7.0 pounds per square inch, the EPA said in a statement on Monday.

The fuel supply shortage was caused by unplanned outages at the Big Spring refinery and Marathon's El Paso refineries.

The temporary waiver, effective immediately, would allow regulated parties to produce, sell, and distribute gasoline in the county with an RVP of no more than 9.0 psi, or 10.0 psi for gasoline containing between 9% and 15% ethanol, the EPA said.

The EPA website says the agency regulates vapor pressure of gasoline sold at retail stations during the summer ozone season from June 1 to Sept. 15, "to reduce evaporative emissions from gasoline that contribute to ground-level ozone and diminish the effects of ozone-related health problems."

Delek, which operates the 75,000 barrel-per-day Big Spring refinery, and Marathon which runs the 133,000 bpd El Paso refinery, could not be immediately reached for comment.

The Big Spring refinery reported an equipment malfunction to the TCEQ on Aug. 14 but it was not clear if this was the same unplanned incident referenced in the EPA waiver. (Reporting by Sherin Elizabeth Varghese in Bengaluru; Editing by David Gregorio)