Hi again Johan.
sorry about mis spelling your name before,
just some info on NOx emissions on Gas v.s. Diesel

U.S. Department of Energy-supported studies have strongly suggested that the strict control of NOx emissions may have the unintended consequence of making ambient ground-level ozone worse. The California Air Resources Board (CARB) has put increasingly strict emission limits on NOx emissions in an attempt to reduce ground-level ozone (ozone is an inhalation health concern), for which Southern California is notorious. However, many previous studies have shown that ozone levels are actually higher on weekends (WE) than on weekday (WD) (WD/WE effect) when diesel truck traffic decreases relatively much more than automobile traffic (which mostly are powered by gasoline engines). The DOE studies have confirmed that NOx is reduced significantly more than VOC (HC) and as a result ozone levels increase. It has been discovered that most large urban areas in the U.S. have similar conditions in which ambient ozone levels rise with decreasing ambient NOx levels and that NOx controls in Southern California (and other urban U.S. locations) are generally counterproductive for reducing ambient ozone, they actually increase ambient ozone levels. Were it not for large concurrent HC emission reductions on weekends, weekend ozone would be even higher than it is, and the weekend/weekday ozone difference would be even larger. DOE concludes that gasoline exhaust and gasoline vapor account for ~80 percent of ambient NMHC (VOCs) in on-road samples and at regional air monitoring locations suggesting that gasoline emissions are responsible for the majority of ozone found in the SoCAB. Whether these recent findings change CARB's (or even EPA's) ozone control strategy remain to be seen.

In addition, other recent studies are suggesting that carbon monoxide (CO) emissions (most of which are from gasoline engine vehicles) are becoming more and more responsible for generating ground-level ozone. The National Research Council's (NRC's) report confirmed the importance of carbon monoxide in the formation of urban ozone, concluding that more than 20 percent of vehicle-related ozone pollution comes from carbon monoxide. The Council also notes that carbon monoxide emissions will play an even larger role in ozone formation as volatile organic compound emissions from vehicles continue to decrease. Another source concludes that CO emissions may be responsible for as much as 35% of the ground-level ozone.

CARB (and to a slightly lesser extent EPA) focuses on reducing NOx. But atmospheric scientist Gary Whitten of ICF Consulting notes that if the tradeoff of reducing NOx is to increase hydrocarbon and carbon monoxide emissions, the environment would be poorly served. The reason, according to Whitten, is that a reduction in hydrocarbon and carbon monoxide emissions has a much greater beneficial impact on ozone formation than an equivalent reduction in NOx. Whitten concludes, "The effectiveness of THC for reducing ozone in these simulations must be as much as 8 times better than NOx reductions on an equal percentage of the mobile emissions basis." Since diesel engines tend to have significantly lower emissions of CO and HC (VOCs), while generally higher emissions of NOx, one could conclude based on these recent studies that an increasing market share of diesel-powered cars and light trucks will have a positive impact on ground level ozone rather that the negative impact which has always been assumed.

So for me i dont buy into the NOx emmisions problem with diesel.

The current move to partiulate filters is great, and hope to see them on both gas and diesel engines. But, what of all the carsengenic emmisions from gasoline.. alkenes, carbonyls, and semivolatiles /PAHs ???

(sorry for the long posts but you asked)