The acoustic theory to measure the volume fraction of suspended particul ate matter in the air

Suspended particles are a general term for solid and the liquid particulate matter suspended in the atmosphere. Total suspended particles in air quality evaluation are an important general pollution index. This paper aims to find a simple acoustic method to measure the volume of the total suspended particles. In order to measure the volume fraction of suspended particulate matter in the air, we studied the effect of the volume fraction and the density of the suspended particulate matter on the speed of the sound wave in the air. We considered the suspended particulate matter to the vibration model of the air, and get the equivalent sound velocity by solving the equation of the mass conservation and the energy conservation of the air element when they are vibrating. We found that, the sound speed of the mixture will be affected by the density and the volume fraction of the suspended particulate matter, it will decrease with increasing the particle density when ones keep the volume fraction constant, and so does the volume fraction when ones keep the particle density constant. So we think that, in a certain range of error, the volume fraction of the suspended particulate matter can be determined by measuring the sound velocity in the mixture of the solid particles and air.