Understanding Euro Emission Standards

At Dowleys, we always aim to give our customers as much information as possible, to help make an informed choice when buying a vehicle.

You may therefore have seen some details in the names of our vehicles which refer to "Euro 6" and "S/S". For example, "SEAT Ibiza 1.0 TSI XCELLENCE Lux Euro 6 (s/s) 5dr" or "Suzuki Vitara 1.4 Boosterjet MHEV SZ-T Auto Euro 6 (s/s) 5dr".

At first glance these details may seem like mere jargon but in fact they refer to important features of the vehicle, covering emissions and economy.

Read on for more information on why understanding these terms can help motorists make a smart choice of vehicle.

Euro emission categories (Euro 1–6/7)

The Euro emission categories are a series of European Union standards that set limits on the amount of harmful pollutants vehicles can emit. Although Britain has left the EU, these standards are still recognised in the UK, and have important functions which we will explain below. They mainly control:

  • Nitrogen oxides (NOx)

  • Carbon monoxide (CO)

  • Particulate matter (PM)

  • Hydrocarbons (HC)

Since first establishment in 1992, each new "Euro" stage has set progressively stricter limits, so a Euro 6 car produces lower emissions than a Euro 4 car, for example.

  • Euro 1 (1992) – the first step, introduced catalytic converters.

  • Euro 2 (1996) – tighter CO and HC limits.

  • Euro 3 (2000) – separate NOx limits for the first time.

  • Euro 4 (2005) – further reductions in NOx and PM.

  • Euro 5 (2009/2011) – diesel particulate filters became common.

  • Euro 6 (2014 onward) – big NOx reductions for diesels.

  • Euro 7 (expected 2025/26) – will apply stricter rules, including brakes and tyres emissions.

Why do Euro emission categories matter?

These standards are important because they are factors in costs associated with motoring..

  • Vehicle tax
    While one might have assumed that compliance with Euro emission categories should postitively affect a vehicle's liability for tax (e.g. the higher a vehicle's compliance, the lower the cost of of vehicle tax might be), UK vehicle tax rates were actually based on C02 emissions, which are not covered by Euro emission standards. From 2025, new changes to vehicle tax futher complicate the picture, depending on when the vehicle was first registered.


    Rates for cars first registered on or after 1 April 2017 are determined by one of three vehicle tax bands - zero, standard or premium. A sliding scale of tax increasing with C02 emissions is applied on new cars, and in subsequent years tax will apply at a set standard rate (even for EVs) or at an additional Premium rate for vehicles worth over £40,000, over the first 5 years the standard rate is applied.

    For cars registered between 1 March 2001 to 31 March 2017, the rates are split into different CO2 bands – the lower the tailpipe emissions, the lower the vehicle tax. Again, higher Euro category vehicles may well have an advantage on reducing tax rates, assuming this means generally lower emissions, but it is not a factor on tax calculations as the other pollutants are not considered, only C02 emissions.

  • ULEZ/LEZ compliance
    This is a topic where Euro standards really do lead to direct reduction in costs. Drivers whose vehicles enter Ultra-Low Emission Zones (ULEZ) in London must ensure their vehicles meet specific Euro standards for emissions (e.g. Euro 4 for petrol cars, Euro 6 for diesel cars), to avoid paying a daily charge (£12.50 at the time of writing, August 2025). A LEZ charge applies to commercial vehicles. Other UK cities including Birmingham, Bristol, Bath, Bradford, and Sheffield have Clean Air Zones (CAZs) with similar, but different, regulations. In Scotland, Low Emission Zones (LEZs) are in force in Aberdeen, Dundee, Edinburgh, and Glasgow.
     
  • Resale values
    With stricter emission standards, older cars which do not meet standards are becoming less desirable to buyers, both due to the potential for direct costs such a ULEZ charges, and general concern about the environment. Their resale value therfore decreases. By contrast, newer vehicles which meet the higher standards may attract a premium, as the vehicle is eligible for LEZs and CAZs, meaning lower costs, future-proofing (if the vehicle meets expected future standards), a perception of generally higher standards in terms of reputation, and a perception of cleaner, more environmentally friendly motoring.

What does S/S mean?

When you see something like “Euro 6 S/S”, the S/S stands for Stop/Start system.

  • This is a fuel-saving and emissions-reducing feature.

  • When the vehicle is stationary (e.g., at traffic lights), the engine automatically shuts off.

  • It restarts instantly when the driver presses the clutch or accelerator.

It doesn’t change the emission category, but it’s often listed in specs because it helps cars meet fuel economy and CO₂ targets.

In short:

  • Euro category = emissions standard.

  • S/S = Stop/Start system fitted.

European emission standards for passenger cars (Category M), g/km

Tier

Date (type approval)

Date (first registration)

CO

THC

NMHC

NH3

NOx

HC+NOx

PM

PN [#/km]

Brake PM10

Diesel

Euro 1

July 1992

January 1993

2.72 (3.16)

0.97 (1.13)

0.14 (0.18)

Euro 2

January 1996

January 1997

1.0

0.7

0.08

Euro 3

January 2000

January 2001

0.66

0.500

0.56

0.05

Euro 4

January 2005

January 2006

0.50

0.250

0.30

0.025

Euro 5a

September 2009

January 2011

0.50

0.180

0.230

0.005

Euro 5b

September 2011

January 2013

0.50

0.180

0.230

0.0045

6×1011

Euro 6b

September 2014

September 2015

0.50

0.080

0.170

0.0045

6×1011

Euro 6c

September 2018

0.50

0.080

0.170

0.0045

6×1011

Euro 6d-Temp

September 2017

September 2019

0.50

0.080

0.170

0.0045

6×1011

Euro 6d

January 2020

January 2021

0.50

0.080

0.170

0.0045

6×1011

 

Euro 6e

September 2023

September 2024

0.50

0.080

0.170

0.0045

6×1011

Euro 7

   

0.50

0.080

0.170

0.0045

6×1011

0.007

Petrol

Euro 1

July 1992

January 1993

2.72 (3.16)

0.97 (1.13)

Euro 2

January 1996

January 1997

2.2

0.5

Euro 3

January 2000

January 2001

2.3

0.20

0.150

Euro 4

January 2005

January 2006

1.0

0.10

0.080

Euro 5a

September 2009

January 2011

1.0

0.10

0.068

0.060

0.005

Euro 5b

September 2011

January 2013

1.0

0.10

0.068

0.060

0.0045

Euro 6b

September 2014

September 2015

1.0

0.10

0.068

0.060

0.0045

6×1011

Euro 6c

September 2018

1.0

0.10

0.068

0.060

0.0045

6×1011

Euro 6d-Temp

September 2017

September 2019

1.0

0.10

0.068

0.060

0.0045

6×1011

Euro 6d

January 2020

January 2021

1.0

0.10

0.068

0.060

0.0045

6×1011

Euro 6e

September 2023

September 2024

1.0

0.10

0.068

0.060

0.0045

6×1011

Table source: Wikipedia

Notes

  • ULEZ (London & expanding cities):

    • Petrol: Euro 4 and above compliant

    • Diesel: Euro 6 only compliant

  • VED (road tax): Based largely on CO₂ emissions, but Euro standard also matters for older bands.

  • S/S (Stop/Start): Often added from Euro 5 onwards to help cars meet CO₂ targets.