In general, an aerosol is any particle afloat in the air (or atmosphere), that is not in the gaseous state as the air molecules such as oxygen or nitrogen are. They are dust particles in the solid or liquid state, small enough not to fall down immediately. The origin and composition of these particles may vary widely. For example: as soon as the dust samples on the image on the lefthand side get airborne, they are considered to be aerosols or particulate matteras it is often called. But also floating pollen or spores of plants and fungi, smoke and industrial soot or even sea salt and water droplets can be considered to be aerosols.
Some aerosols are completely natural, and form no cause for alarm. Other particles emitted by mankind (anthropogenic aerosols) are an important pollutant with a large impact on our lifes. Even natural aerosols can have such an impact, such as pollen have on allergic people. At the same time, there are anthropogenic aerosols that are completely harmless. I turns out to be quite difficult to measure all the aerosol properties that we are interested in. With iSPEX we propose a new measurement method.