1. Airborne particulates produced as a combustion product. These affect air quality, and their emission and ambient concentration is often regulated. For example, coal ash can consist of oxides of silicon, aluminum, iron, calcium, magnesium, sodium, potassium, sulfur, and titanium. 2. Airborne particulates produced by a volcano. These are often fine particles of rock with very sharp edges, which cause great abrasion and wear when ingested in the air intake of an engine, and can quickly lead to engine failure.