@Faheem12
I am not that bad that you want to get rid of me :-). Modern petrol cars are environmentally friendly because these are equipped with elctronic catalyzers. These devices are three stage filters and they filter NO, CO and sulpher elements from the exhaust. Newer emission control policies which are unluckily not enforced in Pakistan prefer petrol engines. Modern cities like capitals and trade centre metropolitans have stricit emission policies. For example in Beijing, where I live every single car undergo a test every two yrs. They measure the exhaust gases and gives you a green, blue , yellow or red sticker. Any car with yellow will not enter city centre and if given red will go to scrap yard. I have hrdly seen any diesel engine clearing this test with green sticker. A corolla without a catalyzer will get a blue. However, BMW, Merc, Lexus, accord, Audi, and other high end brands are all petrol. All buses are on either CNG or LPG. 5000 buses in Beijing are on CNG / LPG. No bus is on Diesel. Deisel trucks if they have to enter city they enter at 2300 and must quit before 0700.
My 1000 cc Geely, EFi without catalyzer is with a blue sticker though it has only 10k on meter.
A properly tuned petrol engine is much better than a properly tuned Diesel engine as far emission control is concerned.