Table 1.
GSD sensitivity analysis results for different definitions of mass efficiency
| GSD 1.25 |
GSD 1.86 |
GSD 2.20 |
GSD 3.00 |
|
|---|---|---|---|---|
| Generated aerosol | ||||
| CMD [nm] | 75 | 75 | 75 | 75 |
| MMD [nm] | 87 | 238 | 484 | 2803 |
| GSD | 1.25 | 1.86 | 2.20 | 3.00 |
| Cumulative mass concentration [mg m−3] | 20 | 20 | 20 | 20 |
| FFP2 mask | ||||
| MPPS of filter [nm] | 65 | |||
| Efficiency at MPPS | 94.5% | |||
| Overall mass efficiency | 96.4% | 98.5% | 99.0% | 99.7% |
| Mass efficiency for particles <0.3 µm | 96.4% | 98.2% | 98.4% | 98.5% |
| ePM1 85% filter | ||||
| MPPS of filter [nm] | 134 | |||
| Efficiency at MPPS | 60.0% | |||
| Overall mass efficiency | 67.1% | 70.0% | 81.6% | 96.7% |
| Mass efficiency for particles <0.3 µm | 67.1% | 64.6% | 65.1% | 65.6% |
| ePM1 55% filter | ||||
| MPPS of filter [nm] | 110 | |||
| Efficiency at MPPS | 11.0% | |||
| Overall mass efficiency | 12.0% | 19.9% | 37.0% | 77.6% |
| Mass efficiency for particles <0.3 µm | 12.0% | 14.4% | 15.3% | 15.9% |
GSD, MMD, and CMD are linked by the equation MMD = CMD exp(3 ln2 GSD) for a lognormal distribution5. Increasing MMD or the dispersion of the test aerosols tends to overestimate the OME, driven by a higher concentration of larger particles that are easily captured. However, this phenomenon is less evident for filter media with high efficiency, like FFP2 masks. For instance, when the efficiency is close to 100% at MPPS, shifting the particle size distribution towards larger will not increase the efficiency appreciably. The underlying conceptual mistake remains hidden since the lowest efficiency is already nearly 100%. The same does not occur when testing filters with lower efficiency (ePM1 85% or ePM1 55%).