Figure 2.

Filter penetration in the morning (AM) and in the afternoon (PM) for four N95 FFR models (A, B, C, and D) against ambient Laboratory 2 aerosol. The CMD was smaller in the morning than in the afternoon on Days 1–4 and showed a reverse trend on Day 5. Top panels show the average penetration values on Days 1 and 2 at 30 l min⁻¹ (top left) and on Days 3 and 4 at 85 l min⁻¹ (top right). Bottom panels show the penetration values at 30 and 85 l min⁻¹ on Day 5.