Hall Magnetic sensors for particles detection have been explored over the past decades. It has been mentioned that the detection has the potential in the applications of biomedicine and environmental monitor. In biomedicine, numerical researches of Hall sensor have been achieved for detecting bio-markers magnetic nanoparticles (MNPs). On the contrary, Hall sensor for environmental monitor is seldom investigated. This paper carries out a pioneering investigation on Hall sensors for air quality detection. A modelling base on finite element method (FEM) software COMSOL is established to quantify the ability of Hall sensors in the measurement of micrometer-sized magnetite particles distributed in the air. Meanwhile, as the development of environmental magnetism in recent years, the modelling has the potential to provide the first protype of portable sensors for the detection of microsized magnetite particles in the air in the future.