Coarse mode respiratory aerosols can carry viral loads over long distances and have very different dynamics than submicron particles, but experimental studies under realistic conditions remain limited. To study the differential impacts on exposure under different mixing conditions, we co-released 7–10 µm particles and carbon dioxide (CO2)—which served as an indicator of gas and submicron particle dynamics—in a 158 m3 room at LBNL’s FLEXLAB facility with an overhead heating, ventilation, and air conditioning (HVAC) system. The room was arranged as a distanced meeting then a classroom with eight heated manikins and a researcher. Spatial variability was measured using 16 particle counters and 22–26 CO2 sensors throughout the space. Conditions included: HVAC off or supply air at 1000-1060 m3 h-1 at neutral, cooling, or heating temperatures; with and without 20% outdoor air; and added HVAC filtration, portable air cleaners (PACs), or a physical barrier between the speaker and occupants. We found that good mixing via neutral or cooling supply air or use of PACs under heating lowered coarse particle exposure at some locations, but increased exposure for one-quarter to two-thirds of manikins compared to poor mixing under heating. A physical barrier reduced direct transfer of coarse particles during heating, but less during cooling. High spatial variability shows that a single measurement cannot represent occupant exposure. Instantaneous air mixing assumptions overstate the effectiveness of ventilation, HVAC filtration, and upper-room germicidal ultraviolet disinfection for coarse particles, as relatively few particles reach the return grille or upper room under most conditions.
BT - Building and Environment DA - 04/2026 DO - 10.1016/j.buildenv.2026.114333 N2 -Coarse mode respiratory aerosols can carry viral loads over long distances and have very different dynamics than submicron particles, but experimental studies under realistic conditions remain limited. To study the differential impacts on exposure under different mixing conditions, we co-released 7–10 µm particles and carbon dioxide (CO2)—which served as an indicator of gas and submicron particle dynamics—in a 158 m3 room at LBNL’s FLEXLAB facility with an overhead heating, ventilation, and air conditioning (HVAC) system. The room was arranged as a distanced meeting then a classroom with eight heated manikins and a researcher. Spatial variability was measured using 16 particle counters and 22–26 CO2 sensors throughout the space. Conditions included: HVAC off or supply air at 1000-1060 m3 h-1 at neutral, cooling, or heating temperatures; with and without 20% outdoor air; and added HVAC filtration, portable air cleaners (PACs), or a physical barrier between the speaker and occupants. We found that good mixing via neutral or cooling supply air or use of PACs under heating lowered coarse particle exposure at some locations, but increased exposure for one-quarter to two-thirds of manikins compared to poor mixing under heating. A physical barrier reduced direct transfer of coarse particles during heating, but less during cooling. High spatial variability shows that a single measurement cannot represent occupant exposure. Instantaneous air mixing assumptions overstate the effectiveness of ventilation, HVAC filtration, and upper-room germicidal ultraviolet disinfection for coarse particles, as relatively few particles reach the return grille or upper room under most conditions.
PY - 2026 T2 - Building and Environment TI - Influence of overhead HVAC and aerosol control strategies on coarse mode particle dispersion and exposure in a full-scale room experiment UR - https://doi.org/10.1016/j.buildenv.2026.114333 VL - 293 ER -