Just a thought…..
Acoustic Engineers who sometimes aren’t Chartered Engineers (sorry for the bias) assess car park ventilation systems on the basis of noise levels against the occupational health standards applicable to workplaces, and that can be subjective depending upon the workplace classification selected.
It’s often better to adopt a performance-based assessment against air quality standards, where natural air-flow is taken into account and possibly optimised to reduce forced ventilation frequencies, and to thereby reduce the noise and energy impacts of that.
I’d suggest you ‘google’ Air Quality Monitoring and get some quotes. I’m sure you’ll find more interest for a lower cost and possibly a better outcome all ’round.