London Low Emission Zone - Feasiblility Study

egr valve
nox is caused by heat, the egr valve gets rid of some of the heat by sending some of the exhaust gas back through the motor

the passing limit is 1500 my cars reading was 2700. I was wondering what could i do to lower it i changed the manifold, cat converter, graduated or did the cars timing, the first reading was 3200 the second reading was 3500 after changing the cat converter, i also took it to the mechanic and [...]

Yes, the EGR is the most likely cause. Other causes are a bad catalytic converter, of a high operating temperature caused by a faulty thermostat, low coolant, or a cooling fan not working.

Unfortunately, I learned this during a vehicle inspection whereas it failed the emissions portion of the test.
HC and CO were low… no check engine light… cat is new (old had NO catalyst element inside)… new secondary ignition… new distributor assy (pick-up coil broke apart and the windings ended wrapped around the shaft)… new timing belt.
At [...]

HIGH SPEED LOW SPEED
STD. [...]

My 92 Olds Cutlass Ciera 3.1 L V6 fails NOx emission. Other emission test criteria are OK. Got new catalytic converter and muffler on. They did not help. Any suggestion about part repairs or replacement to reduce NOx level? Thank you!
Thanks to Archer Christifori for taking time to respond to my question.
Here is some additional [...]

NOx is a generic term for mono-nitrogen oxides,
and are produced with the combustion of fuel.
Nitrogen enriched gasoline is a recent product
of Shell that makes claims of all sorts of things.
In reality, this ‘nitrogen enriched gasoline’ is
nothing more than a gasoline additive. It is
just another of the additives that are allowed
by the EPA. Additives are required [...]

tell me what this could be caused from? My check engine light came on too.
The reason you go to these places is so they can tell you how well it runs and what is wrong if you have a problem. Many times it can be as simple as a bad gas cap to a bad [...]

on the co’s it barly failed. and the car dose not have a egr valve what else could it be?
You most likely have two different issues to deal with.
CO is partially burned fuel, and is a sign of too much fuel for the air in the engine.
The causes can be —
1) Lazy or defective [...]

In atmospheric chemistry ppm refers to ‘parts per million by volume’ so in essence 1 ppm = 10^-6 cu.metre
So V = 10^-6 cu.metres
Now use the ideal gas law (PV=nRT) to determine the number of moles (n) and multiply that by the average molecular weight of NoX to determine the mass.
This will give [...]