The answer will depend on what the question or application is that you are envisaging. What exactly do you want to calculate/estimate? Where, over which area and time period?

Vehicular Emissions for 6 months in Visakhapatnam Urban, A.P., INDIA

I think it would be wise to first find out the numbers and types of vehicles on the road in your area. Important distinctions to make are fuel/technology and builiding year. Both of those are very important in selecting the correct emission factors. The Indian Bharat standards mirror the European emission legislation (Euro types). For other vehicles that are ubiquitous in Indian urban areas (e.g. two stroke twowheelers and CNG powered threewheelers look for other authors who estimated emission factors (e.g. Ragini Kumari for Delhi).

Otherwise the question is still a bit vague;

Which pollutants to you want to estimate (PM, NOx, CO, ....)?

Do you want to estimate the total over 6 months or the (hourly) emission over a period of 6 months?

Thank you Mr. Luc Panis, that's quite useful info!

All the major vehicular pollutants.......hourly emissions (better modelling aspect)..........

When estimating the total emissions, you will also need to find data on the (average) mileages of the vehicles. If you want hourly emissions, you will need to find data on the hourly mileages by vehicle type either by estimating them from annual or daily averages or by deriving them from a traffic model.

Maybe you could take a look at this thesis first and then decide on the methodology to follow. If you request a full text I may be able to upload the full text. I'm not sure how to do it right now.

Thesis ESTIMATION OF AUTOMOBILE EMISSIONS IN DELHI IN RELATION TO V...

That's very useful info! Thank you so much Mr. Luc Panis!

Here is the full text. I did not succeed in uploading it to RG.

Thanks for the help Mr. Luc Panis!