A couple of threads have discussed GHG emissions of EVs compared to the Prius. This thread is meant to discuss another important pollutant, NOx. Data is from EIA - Electricity Data, Analysis, Surveys for the 2009 year, which I think is the most up to date available. The next report from the EIA comes out in late 2011, I presume for 2010. I calculate average Nox emissions in grams/kwh, although it is certainly true that localities vary from the mean, and averages do not take into account source fuel from marginal EV demand on the grid. So without futher ado: Nox generation in the US in 2009 for electric generation: 2395 * 10^9 grams = 2.395 * 10^12 grams Electric generation in the US in 2009: 3.95 * 10^9 Mwh = 3.95 * 10^12 kwh grams of Nox/kwh = 0.606 An EV travels about 3 miles per kwh, so the Nox emissions per mile is 0.202 grams/mile. Now the Prius: 0.003 grams/mile according to this thread http://priuschat.com/forums/gen-iii-2010-prius-main-forum/61282-2010-prius-emissions-numbers.html Relative emissions of an EV vs a Prius: 202/3 = 67 Fold. That is worth repeating: An EV running off the 'average' US grid today emits 67 times as much Nox as a Prius. That should be kept in mind when rational people discuss EV as a public policy initiative. Personaly, I have decided that a clean energy source will have to be available before I fulfill my desire to buy an EV.
I think your units are wrong? EIA report is in thousand metric tons, so it's just moving the decimal to get to grams.. so it's closer to 1 g/kWh, I think...
And note that the analysis would generally go in the other direction for CO.. only 590 thousand metric tons of CO in 2002 from electricity generation (latest data available). So roughly 1/10th of the emissions, and a Prius has ~10x more CO than NOx. But CO isn't as important of a pollutant.. there are currently no CO nonattainment areas.
Right you are that the tons are metric, or about 10% larger than a US ton. Thanks for pointing out the error, I corrected the numbers.
^^ There is something about these numbers I have not sorted out to my satisfaction though. Look at this graph from the EPA IIRC, electric generation and transport in the US are about equal energy amounts, accounting for 1/4rth of the total each. Since Prius is only a tiny fraction of total transport, this suggests that average transport is also ~ 115X fold dirtier than Prius on a Nox/energy_unit basis. True ?
I can't speak to the 115x figure, but the general point is accurate, on-road is much dirtier on average. That is where some of the push to EV comes from, because on a zoomed-out view it appears that EV would be cleaner than gasoline vehicles. But as you already know it fails because EVs, so far, tend to displace the cleanest/most-efficient vehicles. Some recent modeling I just completed is an example of this. I had two scenarios, 200 cars/light trucks commuting 14 miles each; and 40 heavy-duty trucks with a mix of idling and small movements about a parking lot. The trucks have nearly triple the NOx emissions, despite the fact that they aren't even going anywhere. About 80% of the emissions are from idling. We're talking about 0.003 g/mi for a Prius... it's about 1.4 g/mi for your average car. And then it's 144 g/hr for an idling HDDV. The latest push in this area is providing auxiliary power at truck stops so that they don't have to idle as much. Only about 40 locations nationwide, though (per doe).
One thing that needs to be kept in mind is that the 0.003 g/mi NOx emissions from the Prius are "tailpipe" emissions. EVs like the Leaf technically have no "tailpipe" emissions, however, they have relatively high "upstream" emissions. "Upstream" emissions also need to be taken into account for the Prius. Again according to the GREET model, the Prius would produce "well-to-wheels" NOx emissions of about 0.104 g/mile while the Leaf would produce abour 0.231 g/mi, i.e., over twice as much NOx per unit distance driven, based on the EPA "fuel mileage" estimates of the Prius and Leaf. This is graphically illustrated generically in a presentation by the principle GREET developer, Michael Wang... Source: Wang, "GREET Life-Cycle Analysis of Vehicle/Fuel Systems." Argonne National Laboratory, http://www.iom.edu/~/media/Files/Activity%20Files/Environment/EnvironmentalHealthRT/WangGREETPresentationtoInstituteofMedicine1107REVISED.ashx , slide #23 Note also that PM2.5 emissions are much higher with a generic EV than a generic hybrid (slide #25), although to be fair, EV is lower than hybrid in VOC and CO emissions, according to GREET.
Average car / Prius = 1400/3 = 466 fold! I'm having trouble accepting that number. I thought LEV or Fed tier II bin 5 was about 10X that of SULEV. Where does the other 46X come from ?
wxman, Do you know why GREET's Pump to Wheel is so much higher than tailpipe in the Prius ? There is no combustion or refining in the pump to tank part of the lifecycle.
It's a generic "midsize" vehicle for all vehicle technologies, with multiple assumptions as to relative mileage, etc. They're elaborated upon in the link I provided in my previous post. IIRC, the hybrid is assumed to be emitting AT the T2B2 level for NOx (0.02 g/mile). In the Prius vs. Leaf example, I used the actual certified emissions of the Prius and adjusted the "well-to-pump" emissions based on the EPA mileage relative to the assumed generic mileage by GREET.
It should also be noted that according to a 2008 report by the the National Academies (National Academies, "Hidden Cost of Energy: Unpriced Consequences of Energy Production and Use."), EVs and plug-in hybrids produced higher "nonclimate damages" than other technologies not only because of the significantly higher "upstream" emissions of current electric generation, but also because (according to the report) emissions produced during the manufacturing phase were up to 20% greater with EV and PHEV. EVs may be a good option where appropriate to reduce dependence on foreign energy sources, but I'm not convinced they will help much with conventional emissions.
The study also used 40 MPG gas-electric hybrid that meets Bin2 (0.02 g/mi NOx). Prius is 50 MPG and NOx emission is 0.003 g/mi. Prius is not represented on the graphs.
Yes this is what I am trying to say too. Prius is a near zero pollution vehicle by most metrics and low CO2. Who said CO2 is the only metric? Not me. There is SOx, NOx, Hg, particulates, radioactive waste, etc etc. Personally I would like to stop acid rain - no SOx, NOx. No more Northeast rust belt for me. Left coast wants EV, fine, Right coast just wants to breathe since we get the left overs in the prevailing winds.
Sage- Have you sorted this out yet? Couple points to consider, of course diesel makes a lot of NOx (ie trucks). Also catalytic converters are 3-way reducing NOx, CO, HC and catalytic activity is enhanced by ultra low sulfur gaso regulations. Your data was 2005 so I am thinking sulfur was still trending down.
