During the summer , pollution is a frequent concern due to increase level ofsmogand ozone , which can harm the lung . Summer heat boosts the formation of ozone , while the appearance of aninversion stratum — an fast layer of air — can trap pollutant in the low-toned atmosphere [ source : EPA ] .
Summer - score fuel has a differentReid vapor air pressure ( RVP)than winter - degree fuel , which contributes to its being ( marginally ) more eco - friendly . RVP is the vapor air pressure of gasoline measured at 100 degrees Fahrenheit ( 38 Celsius ) . Fuels with higher RVP evaporate more easily than those with lower RVP . A particular fuel blend ’s RVP is base on the combined RVP of the constituent that make up the portmanteau . Regulators interest about this evaporation because it kick in to ozone formation .
petrol must have an RVP below 14.7 psi ( Lebanese pound per square inch ) , which is normal atmospheric pressure sensation ; if a fuel ’s RVP were heavy than14.7 psi , excess force per unit area would build up up in the gas tank , and the fuel could seethe and evaporate . reckon on the state and month , gasoline RVP may not outgo 9.0 psi or 7.8 pounds per square inch for summer - grade fuel . Some local regulations call for stricter standards [ source : EPA ] . Because of these varying RVP touchstone , more than 14 dissimilar types ofboutique fuel blendsare sold throughout the U.S. during the summertime [ germ : Gas Buddy ] .
Because RVP standards are higher during the wintertime , winter - grade fuel employ morebutane , with its gamey RVP of 52 psi , as an additive . ( Winter - level gas has about 10 percent butane in its blend ) . Butane is inexpensive and rich , contributing to lower price . Summer - grade fuel might still apply butane , but in lower quantities — around 2 percent of a portmanteau [ beginning : The Oil Drum ] .
In a 2021report , the EPA said that " rough 75 million Americans take a breather clean-living gentle wind today due to [ the seasonal fuel ] program . " Still , the increased price , combined with the use of controversial additives likeethanol(which is less muscularity efficient than gasoline and acquire more smog ) andmethyl tertiary butyl ether(MTBE ) , means that the program may still have its detractors .
In times of crisis or lifelike disasters , the EPA may foreswear the summertime fuel authorisation . On April 29 , 2022 , the EPAissuedan emergency discharge for a higher - ethanol gasoline blend , allowing summer sale of the fuel in an attempt to help lour petrol prices at the pump , which have rise sharply for the most part due to inflation in the U.S. as well as the market jolt because of the Russian encroachment of Ukraine , among other divisor .
Two other office that prompt the EPA to waive summertime fuel mandate were the 2021 ransomware onset that caused the Colonial Pipeline ( which supplies gas to Department of State all along the East coast)to shut downand theCOVID-19 pandemic in 2020 . In the former font , the waiver was to keep fuel price from getting too mellow and in the latter , the dropoff in gasoline requirement think that more time was needed to transition from winter to summer fuel , as gas storage is limited .
