Specific surface area of combustion emitted particles: Impact of primary particle diameter and organic content

Specific surface areas of particles produced at small-scale diffusion flame burners and also in pilot and large-scale fires involving complex fuels are reported and compared. Specific surface area S-BET is determined by BET (Brunauer-Emmett-Teller) analysis and also according to previously developed approach S-TEM relying on the primary sphere based on TEM (Tansmission Electron Microscopy) images analysis. True density is also determined and the respective influences of primary particle diameter (D-PP) and organic carbon to total carbon ratio (OC/TC) are discussed. The present study is the first to propose a careful comparison between TEM and BET specific surface areas of 20 different samples of carbonaceous particles emitted under realistic fire conditions and to bring validity range for such TEM based approach. For samples containing low and moderate OC content (less than 20%), a good agreement between S-TEM and S-BET is reported (within +/- 20% for a confidence interval of 95%), confirming the significant influence of primary particle diameter and the relevance of a purely geometrical description of the surface specific area of soot particles. For larger OC/TC, such approach fails to predict the particles specific surface area within a reasonable confidence interval.