1) Aerosol: small droplet or particle suspended in the atmosphere, typically containing sulfur Aerosols are emitted naturally (e.g., in volcanic eruptions) and as the result of human activities (e.g., by burning fossil fuels). There is no connection between particulate aerosols and pressurized products also called aerosols (see below).

2) Aerosol: a product that relies on a pressurized gas to propel substances out of a container Consumer aerosol products in the US have not used ozone-depleting substances (ODS) since the late 1970s because of voluntary switching followed by federal regulation. The Clean Air Act and EPA regulations further restricted the use of ODS for non-consumer products. All consumer products, and most other aerosol products, now use propellants that do not deplete the ozone layer, such as hydrocarbons and compressed gases.

nbsp;Particles of liquid or solid dispersed as a suspension in gas. 
 NASA Earth Observatory

Suspended particles in the atmosphere which range in size from about 10^-3 µm to 20 µm. Volcanoes, car exhaust, industrial plants, forest fires, and even ocean evaporation fill the Earth's atmosphere with not only gaseous pollutants, but also very small particles. These particles, which include dust, ash, spores, bacteria, viruses, ammonia, organic material, sea salt crystals, and sulfur and nitrogen compounds, clump together with gases and water in the atmosphere to form aerosols. 
Education Glossary of Atmospheric Sciences Data Center