Granted that gas-hybrids probably have lower emissions than most other gasoline vehicles, but the latest “clean diesel” vehicles actually aren’t as “dirty” as organizations like UCS claim (UCS, Sierra Club, etc., base their “dirty diesel” claims on old data).
Generally speaking, the emissions from a MY 2007+ diesel vehicle (i.e., with DPF) are
lower than an equivalent gasoline vehicle. Consider:
- Criteria emissions
Diesel is lower in PM2.5, NMHC, and CO (
http://www.biodieselmagazine.com/art...86&q=&page=all,
http://www.greendieseltechnology.com...sp?ID=418&link=).
Diesel fuel is
far less volatile than gasoline (and biodiesel is far less volatile than ethanol) resulting in far less evaporative emissions from fuel production, distribution, storage, and refueling, and from “running losses”. According to EPA, VOC emissions just from gasoline distribution amount to approximately 475,000 tons (FR, November 9, 2006, page 66077). These emissions would be virtually eliminated if hypothetically the entire transportation fleet was turned over to diesel.
Diesel vehicles will be able to be certified to Tier 2 Bin 5 once urea/SCR after-treatment certification procedures are approved, and has the potential of being classified Bin 2 or SULEV (
http://www.engineeringtalk.com/news/rca/rca138.html,
http://wardsautoworld.com/ar/auto_fu...ism/index.html), and thus PZEV since diesel fuel has such low volatility.
- Unregulated toxic emissions
Diesel vehicles have lower vehicle-out emissions of virtually all unregulated toxic emissions, including benzene (a known carcinogen), acrolein, acetaldehyde, 1,3-butadiene, and formaldehyde (
http://www.vagverket.se/filer/publikationer/2002_62.pdf,
http://epa.gov/nonroad-diesel/2004fr/420r04007c.pdf).
- CO2/greenhouse gas emissions
Not only do diesel vehicles produce about 20% less CO2 emissions than equivalent gasoline vehicles, they produce less emissions of other “greenhouse gases” like N2O (nitrous oxide) and CH4 (methane) (
http://yosemite.epa.gov/oar/globalwa...ry_annex_e.pdf (Tables E-13, E-17)). Furthermore, diesel fuel requires less energy to produce (
http://www.epa.gov/otaq/technology/420r05012.pdf (page 28)) and biodiesel is more efficient to produce than ethanol (
http://www.ur.umn.edu/FMPro?-db=rele...&ID=3113&-Find,
http://www.renewableenergypartners.org/biodiesel.html).
About the only emission in which diesel vehicles are higher is NOx (and as mentioned previously, NOx emissions are being addressed). In my opinion, NOx is the least critical of the criteria pollutants at this time. This is mostly based on the “weekend ozone effect” studies which suggest that lowering ambient levels of NOx relatively more than NMHC (VOC) or CO cause ozone levels (i.e., smog) to increase in urban locations. See:
http://www1.eere.energy.gov/vehicles...eer_lawson.pdf
http://www.arb.ca.gov/aqd/weekendeff...r_wspa_com.pdf
http://www.raqc.org/ozone/Workshop/O...g%20Lawson.PDF
http://www.biodieselmagazine.com/art...51&q=&page=all
http://climateark.org/articles/reader.asp?linkid=32049
http://www1.eere.energy.gov/vehicles...eer_lawson.pdf
http://www.aei.org/publications/pubI...pub_detail.asp
http://www.alabamapolicy.org/PDFs/EnvIndicators.pdf
http://www.heartland.org/Article.cfm?artId=18973
http://www.greendieseltechnology.com...p?ID=403&link=
http://www.greendieseltechnology.com...EER%202006.pdf