Diurnal trends of indoor and outdoor fluorescent biological aerosol particles in a tropical urban area

We evaluated diurnal trends of size-resolved indoor and outdoor fluorescent biological airborne particles (FBAPs) and their contributions to particulate matter (PM) within 0.5-20 mu m. After a ten-week continuous sampling via two identical widchand integrated bioacrosol sensors, we found that both indoor and outdoor diurnal trends of PM were driven by its bioacrosol component. Outdoors, the median [interquartile range] FBAP mass concentration peaked at 8.2 [5.8-9.9] mu g/m(3) around sunrise and showed a downtrend from 6:00 to 18:00 during the daytime and an uptrend during the night. The nighttime FBAP level was 1.8 [1.4-2.2] times higher than that during the daytime, and FBAPs accounted for 45 0 /0 and 56 0 /0 of PM during daytime and nighttime, respectively. Indoors, the rise in concentrations of FBAPs smaller than 1 mu m coincided with the starting operation of the heating, ventilation, and air conditioning (HVAC) system at 6:00, and the concentration peaked at 8:00 and dropped to the daily average by noontime. This indicated that the starting operation of the HVAC system dislodged the overnight settled and accumulated fine bioaerosols into the indoor environment. For particles larger than 1 mu m, the variation of mass concentration was driven by occupancy. Based on regression modeling, the contributions of indoor PM, non-FBAP, and FBAP sources to indoor mass concentrations were estimated to be 93 %, 67%, and 97 % during the occupied period.

Automated summary

This study evaluated the diurnal trends of indoor and outdoor fluorescent biological airborne particles (FBAPs) and their contributions to particulate matter (PM). It was found that both indoor and outdoor PM trends were driven by the bioaerosol component. Outdoor FBAP mass concentration peaked around sunrise and decreased during the daytime and increased at night. Indoor FBAP concentration increased after the HVAC system started and peaked at 8:00 and then decreased. Based on regression modeling, indoor PM, non-FBAP, and FBAP sources contributed 93%, 67%, and 97% to indoor mass concentrations, respectively.