1/ It is not only large droplets that deposit on surfaces. Small particles can deposit on surfaces far from an infector. My simulations using Emissions to Inhaled Deposition (EID) model for a typical classroom. Case A = 1/ ASHRAE 62.1 2019 (not untypical in many classrooms). 
2/ For case A nearly 20% of particles deposit on surfaces + 2% in collective respiratory system of 25 students. For Case D (ASHRAE 62.1 2019 + good HEPA-based portable air cleaner), 7% deposit on surfaces + 1% in colelctive respiratory systems.
3/ Bar plot shows # of particles (0.5 to 4 microns) that deposit in resp system of a single nose-breathing student using ICRP model in EID. Roughly 20% in alveolar region. The remaining (orange) almost entirely in head region. Only a small fraction in tracheobronchial.
Typo --- should have been 1/2 of ASHRAE 62.1 2019
