Toyota did some pretty substantial-sounding testing in 2000, and CARB published it recently. They found the running E10 instead of MTBE as the oxygenate produced 5.5% higher levels of NOx out the tailpipe.

Although its well-known that evaporative emissions increase noticeably with ethanol, I was not aware of any studies showing an increase in NOx (smog precursors).

They mention that CO (also a smog precursor) output dropped 6%. So on balance using ethanol still lowers (barely) the total smog-making emissions. But that is not pointed out. And NOx primarily assists in ozone producton only in the presence of CO, so less CO still means less ozone.

http://www.greencarcongress.com/2006...s_e1.html#more

source doc: http://www.arb.ca.gov/fuels/gasoline...yota_prstn.pdf

While almost interesting, it's not really relevant anymore since MTBE has already been banned. I'd rather see a similar testing done against regular 100% untreated gasoline. The slideshow PDF only compares against MTBE treated gasoline.

MTBE has been banned in a few states, not nationally. The EPA's rule change only removed the requirement for any oxygenation in RFG/tierIIRFG...in anticipation of the upcoming renewable fuels secion of the 2005 energy act requiring ethanol content wich effectively re-requires it in a few years.

Unfortunately, here in Houston, the EPA looks at each pollutant separately. We are currently in non-attainment status in regards to NOx, and we're switching over to E10 soon. This could have a serious impact on our region's ability to meet our NOx requirements.

Jeff