A good answer and example illustrated in the link

https://www.nexsens.com/knowledge-base/technical-notes/faq/how-do-you-convert-from-molarity-m-to-parts-per-million-ppm-and-mgl.htm

Malik, Thanks for your comment. But this example shows how we can convert if we know the liters. In my case, I don't know the liters of the total solution. Instead, I know the molecular mass of NO and exhaust mass flow rate. how I can replace the exhaust mass flow rate which is m/sec to liters.

Number of mole=1g of NO/ (the molar mass of NO=30 g/Mol) =1/30 mol

Use the equality from the ideal gas of 1mol=22.4L of gas, assuming T= 273.15 K and pressure equal to 1.00 atm

1 g of NO=1/30 mol* 22.4L/mol=22.4/30 L= 0.746L

ppm is mol or volume fraction. Usually NO2 is measured, means M_NO2 = 46kg/mol, Exhaust gas is at about M_exhaust 29kg/mol (depends on composition). The mass flow rate [kg/h or kg/s] of the exhaust gas and NO2 should be known:

ppm = 10^6 * m_NO2[kg/h] / m_exhaust[kg/h] * M_exhaust[kg/Mol]/M_NO2[kg/mol]

Sorry g/mol