Motor vehicle emissions are a major anthropogenic source of air
   pollution. In this study, a comparison of amounts of major emission pollutants
   that they regulated in UK was done for three types of automobile includes
   standard petrol, petrol with TWC and diesel. Also a comparison of amount
   of carbon dioxide emission that it is important in green house effect was
   shown in those three types of automobile.

          For this purpose 300 automobiles were chosen after primary investigation
   and pollutants emissions were tested in different condition of engine and
   environmental temperature.

         The result of this study showed pollutant emission includes THC, NOx and
   CO from petrol car was higher than that from diesel engine when engine was
   hot (P<0.001 , P< 0.0228 and p<0.0336 respectively) but amount of those
   emission pollutant in car with TWC was close to amounts from diesel engine .
   The amount of particles from diesel engine was attentionable in comparison
   with  one’s from petrol and petrol with TWC car. Also the results showed that
   CO and THC emission from two types of TWC petrol and diesel car were
   higher when environmental temperature was low. Although amount of CO₂
   in middle speed was lower from diesel engine. In  many cases most light
   hydrocarbons from petrol vehicles with TWC were higher than diesel engine
   that a clear difference was noticeable for amount of toluene emission
   (P<0.004).

          It is not possible to make a direct comparison of environmental
   friendlines of TWC petrol and diesel vehicle. From the present study’s results,
   it is recommendable that petrol car manufactures have to install TWC
   system on all petrol vehicle and government should provide new standard
   and strong legislations for all new and old petrol and diesel vehicles. ‏