New Study on Effects of Decreased NOx Emissions on Ambient Ozone

[wxman]

We have discussed the relationship between NOx, VOC, and ambient ozone for many years at TDIClub ("weekend ozone effect").

There is a new study which appears in the October 2013 issue of Atmospheric Environment which examines the effects of near-zero emissions during a several year study of Tel Aviv, Israel, during the Jewish holiday of Day of Atonement. Apparently, virtually no driving occurs during that day.

The full paper is paywalled, but according to the abstract...

...A dramatic decrease in primary pollutants emissions (83–98% in NO) causes an 8 ppbv increase in ozone at the urban core. Downwind (27 km), ozone decreases by only 5 ppbv. Nighttime O3 is shown to increase to 20 ppbv at the urban sites and 30 ppbv downwind...

(bolded emphasis added)

Ilan Levy, “A national day with near zero emissions and its effect on primary and secondary pollutants.” Atmospheric Environment, Volume 77, October 2013, Pages 202–212, http://www.sciencedirect.com/science/article/pii/S1352231013003488


Too bad that VOC emission reductions are not mentioned. It is possible that VOC levels may not decrease as much as NOx (NO) on a percentage basis since evaporative emissions will still be produced from gasoline storage tanks in the city, along with VOC emissions from parked petrol cars themselves (diurnal emissions).

I may have to revise my assumption that a fleet of pure EVs in urban areas will result in significant reductions in ambient ozone levels!

 

[Diesl]

I thought it was well known that current emissions standards are counterproductive (read: make smog worse) for urban areas.

 

[wxman]

I thought it was well known that current emissions standards are counterproductive (read: make smog worse) for urban areas.

Yes, since all large urban areas in the U.S. have been shown to be "VOC-limited". This study suggests that even with virtually no anthropogenic NOx emissions, ambient ozone ("smog") still actually gets worse, at least in urban areas.

The weekend effect occurs when large reductions in NOx (>50% reduction; mainly from much less diesel truck traffic on weekends) results in either no improvement in ambient ozone levels or ozone levels get worse. The speculation is that larger reductions in NOx than VOCs in VOC-limited areas is the cause of this. It has also been speculated (e.g., by EPA) that huge reductions in NOx emissions (>90%) would result in "NOx-limited" conditions and further reductions in NOx would result in decreases in ozone levels.

This study is the first of which I'm aware that casts some doubt that even huge reductions in NOx emissions will result in lower ozone levels.

 

[wxman]

Here is EPA's explanation of NOx emission reductions large enough to transition VOC-limited areas to NOx-limited...

...due to the ozone disbenefit chemistry described above, modeling only the final rule-related NOx reductions in an area that is VOC-limited can give an inaccurate representation of future air quality. In an area such as this, marginal NOx reductions modeled independently will likely lead to ozone disbenefits. However, there is a level of NOx reduction, even in VOC-limited areas, where enough NOx will have been controlled to result in NOx-limited conditions and as a result ambient ozone concentrations will decrease....

...This modeling indicates that with substantial NOx and VOC reductions (~90% and ~45% respectively), the entire south coast basin will be in attainment for the 8-hour ozone NAAQS by 2024....

EPA, "Regulatory Impact Analysis: Control of Emissions of Air Pollution from Locomotive Engines and Marine Compression Ignition Engines Less than 30 Liters Per Cylinder." May 2008, pages 2-38 - 2-39

 

[romad]

My head is spinning. "disbenefits"? Sounds like they had to release the report so they could read it!

 

[Diesl]

Here is EPA's explanation of NOx emission reductions large enough to transition VOC-limited areas to NOx-limited...


EPA, "Regulatory Impact Analysis: Control of Emissions of Air Pollution from Locomotive Engines and Marine Compression Ignition Engines Less than 30 Liters Per Cylinder." May 2008, pages 2-38 - 2-39

This website tries to explain it with this picture:

If you are at point A on the red High Ozone (H) line, then reducing NOx = going vertically down first moves you into the area to the right of the red line where ozone actually is higher, but if you keep reducing NOx = going further and further down, eventually you will cross the red line again, and move to lower ozone concentrations.
But it is true that firing up a single diesel without NOx converter at point A will reduce ozone, by going from the red curve up in the direction of the green M middle ozone level curve.

Interesting that in North Carolina it's the trees that are the culprits for the VOC emissions... damn' trees ruining it for all of us! If you are at high NOx (like point A) then the fastest way to reduce ozone is to cut down all your trees (moving left). I have the feeling this is not the conclusion the EPA wants us to come away with.

 

[wxman]

Thank you for that graphic.

Here is another with basically the same depiction...

Source: Eric Fujita, et al, "Weekend/Weekday Ozone Study in the South Coast Air Basin." http://www1.eere.energy.gov/vehiclesandfuels/pdfs/deer_2002/session5/2002_deer_fujita.pdf


Ambient conditions to the left and above the "ozone ridge line" are "VOC-limited" while ambient conditions to the right and below the ridge line are "NOx-limited". This graphic also implies that large NOx reductions will transition "VOC-limited" conditions into "NOx-limited" conditions.

The interesting aspect of the subject study is that huge reductions in NO (up to 98%) apparently are still not transitioning the local chemistry into "NOx-limited" conditions as indicated by increases in ozone on those days with huge NO reductions.

 

[johnkennedy]

Nice information, thanks for sharing.

 

[mr_y82]

Thanks!

I know I am late to the party, but "what he said." ^

most/all? of these I pulled from other places on this site, but it's been a while... so just in case someone stumbles upon this and wants more...

http://webpages.charter.net/lmarz/Diesel.pdf (good read)

http://www.sciencedaily.com/releases/2012/03/120302193928.htm (2012 study mentioned)

http://webpages.charter.net/lmarz/emissions2014.html (based on pre-dieselgate #s.. )

(I definetely found these 3 on the site... Advantages of diesel...)
http://webpages.charter.net/lmarz/performance.html
http://webpages.charter.net/lmarz/efficiency.html
http://webpages.charter.net/lmarz/emissions.html