Systematic experimental comparison of particle filtration efficiency test methods for commercial respirators and face masks

Respirators, medical masks, and barrier face coverings all filter airborne particles using similar physical principles. However, they are tested for certification using a variety of standardized test methods, creating challenges for the comparison of differently certified products. We have performed systematic experiments to quantify and understand the differences between standardized test methods for N95 respirators (NIOSH TEB-APR-STP-0059 under US 42 CFR 84), medical face masks (ASTM F2299/F2100), and COVID-19-related barrier face coverings (ASTM F3502-21). Our experiments demonstrate the role of face velocity, particle properties (mean size, size variability, electric charge, density, and shape), measurement techniques, and environmental preconditioning. The measured filtration efficiency was most sensitive to changes in face velocity and particle charge. Relative to the NIOSH method, users of the ASTM F2299/F2100 method have commonly used non-neutralized (highly charged) aerosols as well as smaller face velocities, each of which may result in approximately 10% higher measured filtration efficiencies. In the NIOSH method, environmental conditioning at elevated humidity increased filtration efficiency in some commercial samples while decreasing it in others, indicating that measurement should be performed both with and without conditioning. More generally, our results provide an experimental basis for the comparison of respirators certified under various international methods, including FFP2, KN95, P2, Korea 1st Class, and DS2.Comment: 34 pages, 8 figures, 3 table

High-Resolution Infrared Spectroscopy of van der Waals Clusters of Nitrous Oxide, Carbon Dioxide and OCS-R Complexes

Weakly-bound van der Waals complexes containing OCS and various hydrocarbons, and clusters of N2O, and CO2 are studied by means of their rotationally-resolved infrared spectra. Clusters are generated in a pulsed supersonic jet expansion with two slit-shaped nozzles and probed with a tuneable diode laser. Study of OCS-R complexes (R indicates certain hydrocarbons with chain or ring structures) commenced with the study of OCS-acetylene complex in the region of nu1 stretching fundamental of OCS (~2060 cm-1). Two bands are observed and assigned to near-parallel and T-shaped isomers of OCS-acetylene. In addition to the normal species, the deuterated isotopic form is also studied. Simple looking bands characteristic of a T-shaped structure are observed for complexes formed between OCS and ethylene, allene, propyne, dimethylacetylene, benzene, and cyclo-octatetraene. All the bands are observed to be red-shifted from the OCS monomer nu1 frequency. Infrared bands in the CO2 nu3 region (~2350 cm-1) are assigned to carbon dioxide clusters, (CO2)N, with N=6, 7, 9, 10, 11, 12, and 13. Assignments are aided by cluster calculations using two reliable CO2 intermolecular potential functions. These are the largest molecular clusters studied by infrared spectroscopy with rotational resolution. Two highly symmetric isomers with S6 and S4 symmetries are observed for (CO2)6. (CO2)13 is also symmetric with S6 symmetry, but all the remaining clusters are asymmetric tops. The bands have increasing blue-shifts with increasing cluster size, similar to predictions of resonant dipole-dipole model but considerably larger in magnitude. N2O tetramer is studied in the region of N2O nu1 fundamental (~2220 cm-1). The previously observed oblate isomer of (N2O)4 is studied with considerably higher resolution. Isotopic substitution has confirmed a structure with D2d symmetry for this isomer. In addition to the oblate isomer, a new prolate isomer of (N2O)4 with S4 symmetry is observed