Over a dozen car models - including some popular mainstays - will not meet the Euro 6 emission standard which kicks in on Friday (Sept 1).

These include popular executive sedans like the Honda Accord, Toyota Camry and Nissan Teana, and budget sedans like the Nissan Almera and Toyota Vios.

Chevrolet's entire range here, along with Suzuki's Swift hatchback and S-Cross crossover, Hyundai's sporty Veloster and Honda's budget seven-seater Mobilio, also do not meet the emission standard.

Existing car models on the road will not be affected by the new rule.

The respective authorised agents plan to bring back Euro 6-compliant versions of some of the cars in due course.

But a few are likely to exit the market for good, including the Nissan Teana, Honda Accord and Honda Mobilio.

While a number of cars will exit the Singapore market come Friday, their absence may not impact that many consumers.

Mr Ron Lim, general manager of Nissan agent Tan Chong Motor, said that consumers have been veering away from sedans towards sport utility vehicles (SUVs) in recent years. Hence the impact of the two Nissan sedans' exit, for example, would not be significant.

Curbing pollution

The aim of Euro 6, the highest emission standard legislated by the European Union, is to reduce levels of harmful exhaust emissions, both in petrol and diesel vehicles. It stipulates lower levels of pollutants than those listed in Euro 4, which has been adopted here. It also adds two more pollutant readings - particulate matter and particulate count - to make a total of seven. Singapore is adopting Euro 6 for petrol vehicles from Sept 1, and for diesel vehicles, from Jan 1 next year.

And despite earlier fears, most - if not all - parallel import models will meet the standard, which was first announced in December 2014.

This is because the National Environment Agency (NEA) deems cars which have port-fuel injection engines and which meet JPN2009 regulation - an emission standard introduced in Japan eight years ago - to be Euro 6-compliant.

Port fuel injection - where fuel is injected just before the engine's combustion chamber - is used widely by Japanese manufacturers.

As proof, the NEA accepts export certificates or third-party certification for parallel-imported vehicles. Authorised agents, however, are required to submit documentation from the vehicle manufacturers "to establish compliance with emission standards and identification of the fuel injection system".

As a number of authorised agents' cars are sourced from Asian plants, their cars are not made to comply with JPN2009. This is because most Asian markets do not require such a high emission standard.

Asked how an eight-year-old Japanese emission standard can be equivalent to the latest European standard, Singapore University of Technology and Design assistant professor in engineering systems and design Lynette Cheah said: "The Japanese motor vehicle emissions standards have been tightened incrementally over time.

"Their 2016 limits are comparable to Euro 6 standards. The standard quoted by NEA refers to limits originally published by Japan's Ministry of Land, Infrastructure and Transport in 2002, but has since been amended and made more stringent a number of times."

While the Sept 1 regulation will see some models exit the market and others become unavailable temporarily, industry experts expect a much bigger shake-up when another emissions scheme comes into effect in January.

The Vehicular Emissions Scheme grants tax rebates or imposes surcharges on cars according to readings of five pollutants: carbon dioxide, carbon monoxide, nitrogen oxides, hydrocarbons and particulate matter.

Under the scheme, a number of small turbocharged engines - popular among European and increasingly, Japanese makes - will attract a surcharge of as much as $20,000, versus a rebate of at least $5,000 now.

Mr Lim from Tan Chong Motor said: "How this will change the whole landscape can only be seen from next year onwards."

Correction Note: An earlier version of the story said the two additional pollutant readings to be added to the scheme are hydrocarbons and particulate count. This is incorrect. They should be particulate matter and particulate count. We are sorry for the error.