This article describes the development of a mathematical model for evaluation of particle concentration for indoor air conditions. The results of modeling could be used to predict particle concentration in an ambient air at different distances from the source, taking into account space geometry and ventilation/air conditioning created air streams. Two case studies were then undertaken to determine the particle concentration at hypothetical shopping center for the situations when: (1) the ambient air movement is created by a local ventilation system, and (2) besides the local ventilation, the outdoor air enters the space influencing particle distribution situation due to mixing with ventilation created air streams. The results of modeling were used to evaluate the minimal source concentration of virus containing aerosols measurable by our recently developed personal bioaerosol sampler moving along various routes during certain time intervals.