TABLE 2.

Sampling methods of air samplers used for SARS‐CoV‐2

Sampling method		Collection mechanism a	Collection media	Flow rate range	Captured particle range (d50, μm)	Advantages	Disadvantages
Passive air sampling	Sedimentation	A petri dish is opened and exposed to the air for specified periods of time to determine what microbiological particles may be present in the environment, as they may settle out of the ambient air and on the media surface of the petri dish	Filter	NA	Depending on the filter porosity	Not aggressive. Lower cost	Qualitative analysis. Collection duration is longer
Active air sampling	Impactor	Particles in the incoming airstream accelerate through small nozzles (in the form of holes or slits), and those with high inertia impact on the surface of collection media	Agar, slide or filter	~1–125 L/min	<1 (single‐stage) or 0.01–10 (multi‐stage)	Collect viruses in different particle sizes. More efficient for larger particles	Wall loss. Virus deactivation upon collection. Low‐efficiency for small virus particles
	Cyclone	Centrifugal forces deviate particles from the airflow to impact on the collection wall	Dry vial	~10–400 L/min	>0.5	Collect viruses in different particle sizes. More efficient for larger particles	Wall loss. Virus deactivation upon collection. Low‐efficiency for small virus particles.
	Filter	Particles are collected on the filter media through interception, inertial impaction, and diffusion	Filter or membrane media	~1–1000 L/min (filter dependent)	Dependent on filter porosity (<1)	Efficient for particles from 20 nm to 10 μm or even larger. Easy to use	Inactivation of viruses due to dehydration or extraction from filters
	Impinger	Abrupt change in the airstream direction inside the bottle impacts particles into the liquid collection medium	Liquid	~10–500 L/min	>1	Maintain viability of viruses. No need to extract viruses from a surface or filter	Wall loss or inlet loss. Low efficiency for small virus particles
	Water‐based condensation	A laminar‐flow condensation growth tube (CGT) encapsulates airborne particles into liquid droplets and gently deposits the droplets on a liquid surface	Liquid	~10–1000 L/min	<0.5	Maintain viability of viruses. Efficient for particles from 8 nm to 10 μm or even larger	Bulky and complex to operate

Abbreviation: NA, not applicable.

^a Adapted from Pan et al. ⁶