Biological agents in aerosol form create a risk via two exposition routes:
Either through minuscule breathable particulates in the air (direct transmission by inhalation)
Or by the deposition of heavy droplets of larger size on surfaces, equipment and personnel which, put back up in suspension mechanically (with wind or sweeping…) can generate still-infectious biological particulates (direct transmission)
Heavy droplet deposition can also contaminate hands and be further transmitted to the mouth and eyes.