We had conducted the Petri dish method to assess the fungal flora in our Zoonoses Laboratory.We used Sabouraud dextrose agar and Pal sunflower seed medium.The culture plates were exposed inside the laboratory for 5 to 10 minutes and then incubated for the growth of airborne fungi.
We have described this technique in the book entitled" Veterinary and Medical Mycology" authored by Mahendra Pal and published by the Indian Council of Agricultural Research New Delhi in 2007.
The most basic method would be to put agar plates with rich media (BHI, Blood Agar) on the shelves and leave them open for 24 hours, then incubate in 37 Celsius degrees and analyse, what kind of bacteria grow there.
More complicated would be to take "samples" of air using a sterile syringe and pass through the 0,22 micrometer filter. All bacteria should be attached to the filter and then you can grow bacteria from the paper disc inside the filter in broth or agar plates. You can also try to isolate DNA from such a sample and use PCR to determine for example 16sRNA sequence to identify the species.
Generally the food industry uses PCA Agar Plates for Aerobic Colony Count and DRBC Agar Plates for Yeast and Mould counts.
Normally exposed for 30 mins to 1 hour.
Pharmaceutical laboratories or areas with controlled filtered air may use longer exposure times and different media
There are air samplers that you can buy to use but again it depends on the industry or environment you are wanting to test the air in and for what goal you are hoping to achieve