What is CO2 g/km emissions equivalent of Euro 4 petrol standard?

Question

I am trying to find what Euro 4 standard is with regards to CO2 g/km. All I can find is that it is:

CO: 1.0g/km
THC: 0.10g/km
NOx: 0.08g/km

This makes no sense to me when trying to compare this to e.g. a CO2 g/km on sites like Autotrader where filter values are:

100 g/km CO2
110 g/km CO2
120 g/km CO2
130 g/km CO2
140 g/km CO2
150 g/km CO2
165 g/km CO2
175 g/km CO2
185 g/km CO2
225 g/km CO2
255 g/km CO2

Answer 1

The Euro 4 (and similar standards) are not about CO2 emissions. They are about other pollutants in the exhaust, as in your table. They apply to all cars, whatever the engine size and fuel consumption.

Note that CO (carbon monoxide) is not the same as CO2 (carbon dioxide). For a "perfect" engine the CO emissions would be zero, but the CO2 emissions depend how much fuel is being used.

The CO2 emissions are related to fuel consumption (miles per gallon or liters per 100km), and the numbers apply to particular makes and models of car.

The CO2 filter levels on sites like Autotrader are because in some countries (e.g. the UK) annual car tax rates are linked to the declared CO2 emissions.

Answer 2

There is a fundamental misunderstanding in the question. Perfect combustion of hydrocarbons (HC, H = hydrogen, C = carbon) produces the oxide of hydrogen and oxides of carbon.

The oxide of hydrogen is water, H₂O.

The main oxide of carbon is carbon dioxide, CO₂, although there is carbon monoxide too, CO. Only imperfect combustion produces CO. Perfect combustion produces only H₂O and CO₂.

Imperfect combustion produces various pollutants as well as H₂O and CO₂:

• One is the carbon monoxide, CO, which I already mentioned. It is fatal even in very small amounts in the air.
• Another pollutant class is oxides of nitrogen, often called NO_x because there are quite many of them with varying x. They are a constituent of smog.
• A third pollutant class is unburned hydrocarbons, called HC (although it's a mystery why they are not called HC_x akin to NO_x because there usually won't be as much H atoms as there will be C atoms). They are too a constituent of smog. Sometimes, methane is separately mentioned and then the non-methane parts are called NMHC and the total amount of methane and non-methane parts may be called THC.
• A fourth pollutant class is particulate matter, called PM. They are typically hydrocarbons, but in particulate form. If they get to your lungs, they can cause respiratory diseases. PM is the main reason unfiltered diesel exhaust is dangerous when inhaled for long periods of time.

Now, these pollutants are some seriously bad stuff, and they should be minimized at all costs. However, both of the non-pollutants, H₂O and CO₂ are greenhouse gases: they increase the temperature of our planet due to radiative forcing. Of these, H₂O has a balance between liquid and gas states, and adding more H₂O just adds more of the liquid while keeping the gas in balance, so fortunately more H₂O does not equate to a warmer planet. Also, there is so much H₂O in the oceans that adding a bit of more won't hurt.

However, CO₂ is a gas with no liquids in the usual temperatures on planet Earth. Thus, adding more CO₂ adds to the amount of gas in the atmosphere directly. The main harm is radiative forcing which creates a warmer planet.

A particular amount of gasoline produces a particular amount of CO₂: 1 litre of gasoline equates to 2.35 kg of CO₂.

There are plants to limit CO₂ which would equivalently limit fuel consumption. However, Euro 4 is so old standard that it does not apply to CO₂ at all. I believe the CO₂ limit standards in the future will be completely separate from Euro N standards where N is the version number. So even Euro 10 if we see such a standard ever won't probably limit CO₂.

Limiting CO₂ is a fundamentally different thing than limiting the harmful pollutants. Traveling a kilometer requires a certain amount of energy, and if the energy source is gasoline, at a certain efficiency a certain amount of gasoline needs to be burned. Limiting CO₂ can only be achieved by better energy efficiency or a more aerodynamic/lighterweight car.

Making the picture more complex is that if the gasoline is created from biological sources, they have captured the carbon from the atmosphere. Thus, even if 1 litre of biofuel creates 2.35 kg of CO₂, it won't add any net CO₂ to the atmosphere because the biological sources have captured the CO₂ already. Thus, limiting CO₂ will be hard: how can the limits take into account biofuel usage? I think they'll just have to assume some percentage of biofuel used (such as 10%). We don't have enough biological sources of gasoline to replace all gasoline usage on this planet.