Emissions are typically defined as kg/s. For most applications, the emission is used in order to evaluate the immission (concentration) at some distance from the source. And for that purpose, the initial concentration (in ppm) is less relevant than the total mass flow or volume flow.

For example, take traffic pollution. The emission is given in m3/h. With the specific density, this translates into kg/s. The initial dilution is driven by the air flow around the vehicle. Therefore, it is irrelevant how much air is going through the engine and what is the initial concentration (in ppm) of the exhaust fumes..

see this paper

Ingo Riess thanks for your valuable explanation, I want to ask if the expression in kg/s unit has to have the same trend with ppm unit or I can't compare between them?

If you want to connect emissions given in [kg/s] and in [ppm], you need the initial concentration, i.e. the airflow that is related to the emission process.

For traffic vehicles, this may either be the airflow through the engine (little helpful for most processes) or an assumption of the initial dilution (e.g. atmospheric wind velocity through an area related to the dimension of the vehicle).

The underlying equation can be found here, as you'll see, the emission Q is given in [g/s]:

https://en.wikipedia.org/wiki/Atmospheric_dispersion_modeling#Gaussian_air_pollutant_dispersion_equation

how did you arrive at kg/s value, is it an experimental value or theoretical findings???

if experimental, what instrument did you use to measure this..???

Mebin Samuel I arrived at kg/s value from Simulation

Ingo Riess that's great, thank you so much

The French Tunnel Ventilation Standard from CETU (les dossiers pilotes du CETU, Ventilation) states on page 34:

CO: 10E-3 ppm 1.14 10E-6 g/m3

NO: 10E-3 ppm 1.23 10E-6 g/m3

NO2: 10E-3 ppm 1.88 10E-6 g/m3

Valid at ambient air temperature 25° C at normal atmosphere

Regards