Combustion engines affecting air quality on hospital sites

We are specifically looking at idling of all types of combustion vehicles on the hospital site. Especially around the ED (drop off and ambulance bays)
1. Has anyone done practical studies on hospital sites to demonstrate the deterioration of air quality with and without idling combustion engine vehicles?
2. Does anyone have signage they have used on their sites?
3. If I was going to do a local project to establish the change in air quality with a local AQ monitor. What monitors do people recommend and what should we consider when testing - times of day, temperatures, season, etc?