The COVID-19 pandemic has brought to fore the importance of understanding generation, transport, and fate of particles from human emissions. Aerosol emissions from human activities such as breathing and talking are of major concerns from an airborne disease transmission perspective, but our knowledge about these particles is largely limited to laboratory studies. In the absence of diverse field studies, there is significant uncertainty in emission rates of these particles, and hence the infection threat they pose. With the widespread usage of masks, an additional layer of uncertainty in emission rates has been introduced. To fill the need for field-based emission rates, we conduct an experimental study monitoring airborne particles in a classroom under varying activities and occupancy levels. We measure size distribution of particles using Ultra-High Sensitivity Aerosol Spectrometer (70 nm – 0.5 μm) and Aerodynamic Particle Sizer (0.5 μm – 20 μm). Additionally, a network of low-cost optical sensors was deployed throughout the room to understand the spatio-temporal distribution of particles. The experimental data under different occupancy loads is analyzed in conjunction with theoretical models to extract air exchange rate, particle loss rate, and emission rates under the scenarios of breathing, breathing and talking, and walking with mask usage. We additionally obtain size distributions of particles under these activity conditions. The results suggest that human aerosol emissions in a real-world setting are lower than that estimated from laboratory studies, with an emission rate from masked speaking of 1 particle per person per hour. The extraction of emission rates under field conditions provides critical data for disease transmission models with masking regulation in place. Follow-up
data obtained after the pandemic measures are withdrawn, will provide a full measure of effectiveness of masks under real-world usage.