I often forget about them because I so seldomly fill a gas powered car. The diesels just have the old school splash guard.Excellent post, Matt!
We used to have those awful gas pump foreskins too. Thankfully they went away some time ago. I forgot about those darn things.
Interesting on the different dollar values placed on the same type of pollutants. I wonder what that's about.According to a recent paper by EPA staff scientists (Wolfe et al., "Monetized health benefits attributable to mobile source emission reductions across the United States in 2025." Science of the Total Environment 650 (2019) 2490–2498), modern gasoline exhaust is about twice as damaging in terms of morbidity and mortality from primary and secondary PM2.5 than modern diesel exhaust:
Damages per Tables 1, 2, 3
On-road Diesel -
PM2.5 - 36,893 tons X $790,000/ton = $29B
NOx - 1,120,172 tons X $9,350/ton = $10.5B
SO2/SO4 - 11,980 tons X $490,000/ton = $5.9B ($45.4B total damages)
On-Road gas -
PM2.5 - 42,088 tons X $1,950,000/ton = $82B
NOx - 556,761 tons X $11,050/ton = $6.2B
SO2/SO4 - 8,238 tons X $210,000/ton = $1.7B ($90B total damages)
With any of those numbers, it sounds like there are many more times VOCs in the air than NOx, for whatever that's worth.One aspect of mobile-source emission regulations for LD on-road vehicles is that exhaust and evaporative VOC emissions are regulated separately, even with Tier 3. This in effect allows LD gasoline vehicles to emit at least 0.05 g/mi more VOC than LD diesel vehicles since evaporative VOC emissions are essentially zero for diesel fuel. That's really an unjustified regulatory benefit given to gasoline vehicles.
There are no reasons I can think of that evaporative VOC emissions shouldn't be included in the exhaust NOx+NMOG limit. I made a comment indicating such in the open comment period for Tier 3, but it was dismissed without response.
I have seen that UC Berkeley article, and the 2.4:1 VOC:NOx ratio is MUCH lower than other atmospheric chemistry studies I've seen, including EPA and what I was taught in grad-level atmospheric chemistry courses, which was 8:1 ratio that divided VOC-limited and NOx-limited regimes. I've seen one recent study that used a 10:1 ratio! Not convinced that Berkeley's ratio is the correct one at this time.
That was the initial reaction I got as well once I understood the weekend effect and heard about the Caldecott tunnel study. There will be a period in some areas where air quality worsens despite the drop in NOx, but in theory should be temporary and once "over the hump" the air quality should improve again.The photochemical reactions among various pollutants in the atmosphere is very complex. Like with Ozone formation, there are two regimes for PM 2.5 formation. The bottom line is that reducing NOx emissions sufficiently will eventually(not always immediately) lead to cleaner air. Seems obvious, but it's true.
What I said previously about there being different optimal VOC:NOx ratios for max ozone production in different studies:Previous research from Thornton's group has shown why winter air pollution is more resistant to emissions regulations than summer smog: because different temperatures provide seasonal conditions that send the chemistry down distinct paths.
All this additional information does, though, is throw into question just how much do the regulators grasp about the situation? Feels like information overload to most, there are some trends to draw from, sure, but it's still not 100% definitive or agreed upon. And being that NOx by itself isn't harmful to breathe in the immediate sense like CO is and the fact that even with all the studies performed, there still isn't 100% agreed upon consensus, how does one expect that journalists are going to be able to cover this topic accurately, especially since they're largely not technical people. They're more information regurgitators and opinion makers than they are properly understanding of the very complex technical subject at hand.It might also not be a fixed ratio depending on other environmental variables. Since the Berkeley study was done in a tunnel, there's no sunlight and it's in a region that doesn't average temperatures near as high as L.A. does, and of course those two items play a big role in the reactions of the two compounds or at least help accelerate it.
And that's exactly what it seems regulations were targetting.Perhaps, but another study suggests that NOx emissions would have to be reduced by 90% from 2008 ambient levels (at constant ambient VOC levels) in order for SoCAB to be in attainment with the O3 NAAQS.
1991 Jetta diesel, still have it.Here I thought you'd never bought a new one!.
I do. I thought I had a photo of it, but I can't find it. That was nice.Remember that one year an NAIAS where MB had that diesel hybrid E-class displayed? Wonder what became of that. Looked to be the OM651 engine coupled to a Bosch hybrid system. Probably pricey, but probably impressive fuel economy on both city and highway driving.
Discussing that in another thread, and it has been tried back in the '80s and early '90s. I think it is best suited for yard lot transfer trucks, as OTR trucks typically cruise at a higher speed and the modern transmissions they use (mostly automated manuals) are pretty efficient at keeping the engine in the sweet spot.Speaking of the electric / diesel powertrain - why couldn't you run the over the road semi the same way as freight trains ? Same plusses / minuses, except there are far more trucks than railroad locomotives.
Only real problem I can see with it is space for both the electric motor and the prime mover generator / fuel for it.
This is one of the operating modes of my ELR... the resulting fuel economy isn't fantastic. Upper 30s / low 40s.Speaking of the electric / diesel powertrain - why couldn't you run the over the road semi the same way as freight trains ? Same plusses / minuses, except there are far more trucks than railroad locomotives.
Isn't that the idea behind the VW 1 liter project? Electric engine charged by a small diesel engine.I still think it would be great to have a diesel engine hybrid with a Chevy Volt-like propulsion system, perhaps with even smaller batteries than the Volt. The engine could run at peak efficiency and let the electric motors provide motive power.