Wildfire smoke contains combustion by-products, which are gases and small particles generated when materials burn. These combustion by-products include ash, soot and char particles.
Ash: Ash is pyrolized material obtained from advanced combustion of char particle that is left when a substance is burned. Ash includes trees and vegetation but can also include building material or any other burned object. Because the carbon matrix of char particle is almost completely combusted, ash is mainly inorganic with a high amount of calcium, potassium, magnesium, aluminum, silicon, phosphorus or sulfur. The ash particles are very brittle and may or may not contain some of the original material’s cell structure. Ash has high pH (9 to 11).
Char: Char is often associated with remnants of burnt wood or damaged building materials. Char particles are produced when a substance or material does not completely burn and is a incomplete combustion by-product. It is darker than ash and can range up to several millimeters in size. Char particulate may not de-agglomerate or disperse by ordinary techniques, may contain material which is not black, and may contain some of the original material’s cell structure, minerals, and ash.
Soot: Soot is frequently referred to as carbon black because of the color, but soot is not carbon black. Carbon black (also known as acetylene black, channel black, furnace black, lamp black and thermal black) is a material produced by the incomplete combustion coal and coal tar, vegetable matter, and petroleum products. Carbon black is a distinct material that is commercially produced under highly controlled conditions and is used extensively as an ingredient to strengthen rubber in tires, but can also act as a pigment, UV stabilizer, and conductive or insulating agent in a variety of rubber, plastic, ink and coating applications.
Soot, on the other hand, is sub-micron black powder generally produced by-product of combustion or pyrolysis of vegetation. Soot is aciniform (cluster of grape-like structure) and consists of varying amounts of carbon and inorganic solids in conjunction with adsorbed and occluded organic tars and resins. Soot contains acids, chemicals, metals, soils, and dust. These particles leave a black stain and foul smell. During a fire, soot spreads to the whole house, and attaching to surfaces.
Structural fires have a different particle distribution, typically with higher ratios of soot particles and other melted plastics, paint and metals.
At Pasteur Laboratory, we use polarized light microscope (PLM) with reflected light source to identify wildfire residues. We recommend using clear tape (not frosted) to collect the samples rather than wipe or micro-vacuuming. When using tapelift, the integrity of the particles remain intact. We provide the same day, 2-day and 5-day turnaround.