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Collecting viral aerosols in a size-segregated fashion is a valuable technique for pursuing several different research questions.
First, there is a desire to understand if the virus is present in airborne particles in a variety of settings. Quantitative biological assays such as polymerase chain reaction (PCR) analysis can be conducted on samples of collected aerosols. This type of analysis can be done when all sizes of particles are present in one sample, but doing size-segregated sampling helps you to dig deeper. For example, knowing the sizes of particles that house the virus may help organizations select or design more effective control measures, such as filtration or PPE design.
To move beyond the question of whether the virus is present, the next question is, is the virus viable. One of the uncertainties surrounding the transmission of COVID-19 is how well the virus maintains its infectivity as droplets dry into smaller particles. Time is a factor here, but aerosol size may itself be a factor. To investigate the effect of aerosol size on the viability (infectivity) of airborne viruses, aerosol samples must be collected in a size-segregated fashion. Biological analyses can then be done on these size-segregated samples to investigate the question of viability.
Cascade impactors are a valuable tool for sampling aerosols in a size-segregated fashion. The TSI 100 MOUDI impactor is a cascade inertial impactor that can segregate the sampled particles in 11 size fractions between 0.18 and 10 mm. This impactor has sharp collection efficiency curves that allow users to assess the virus content and viability of the collected samples as a function of aerodynamic diameter. By using impaction plates filled with Agar media or gelatin filters to collect the samples, appropriate analyses can be conducted on the collected samples to determine infectivity.