## 3 Scientific Background
### \"Condensables\" as a Contributor of Carbonaceous PM
Extremely low-volatile organic compounds (ELVOCs), which are essentially non-volatile under relevant conditions;* EC or BC--contains some atoms of hydrogen but is mainly composed of carbon. This species is usually not defined as an organic species. Categories (i) and (ii) can be always considered in the gas phase regardless of the dilution ratio and temperature. The definition of a volatile organic compound (VOC) varies from country to country. A general scientific definition of a VOC is an organic compound that evaporates or vaporizes under ambient conditions. These gases are emitted from various materials. From a legal point of view, the definition of VOCs can be different; for example, in the National Emission Ceiling directive: _volatile organic compounds' and 'VOC' mean all organic compounds arising from human activities, other than methane, which are capable of producing photochemical oxidants by reactions with nitrogen oxides in the presence of sunlight_. Categories (iii) and (iv) partition between the gas and particle phases depending on the temperature and dilution ratios. The notion of IVOCs is questionable and is addressed further in this review. These compounds, which have saturation concentrations between \(10^{3}\) and \(10^{6}\)\(\upmu\)g m\({}^{-3}\), are termed intermediatevolatility organic compounds (IVOCs) by [PERSON] et al. [136]. The IVOCs category could overlap with the legal definition of VOCs since the degree to which IVOCs have been included with VOC sampling techniques historically is not clear. Recently, [144, 145, 146] has analysed and determined emission factors for IVOCs for different type of domestic fuels including wood. Categories (v) and (vi) can be considered as belonging exclusively to the particle phase. This phase is composed of heavy hydrocarbons and organic species. Species in categories (ii) to (iv) can react in the atmosphere and produce aerosol particles. The products of these reactions fall in categories (iv) to (v) by increasing their molar mass mainly due to the addition of oxygen atoms. A split in volatility classes has been proposed [113, 147] based on saturation concentrations (Table 4). Therefore, organic condensables are species belonging to primary ELVOCs to SVOCs or secondary OA (SOA) categories. We often speak about semi-volatile organic compounds (SVOCs) to name the organic species that would exist in both the gas phase and the particulate phase. In atmospheric chemistry, there can be different definitions of SVOCs. One study proposed to measure SVOCs based on mass collected on a \"bare-Q\" Quartz filter including the primary particle and some fraction of the semi-volatile organic vapour [148]. This definition was taken up by further works [137, 138, 149, 150] to study the gas/particle partitioning of primary OAs. Compounds with an effective saturation concentration C* below \(10^{-3}\)-\(10^{-4}\)\(\upmu\)g m\({}^{-3}\) are generally captured with such a method. [PERSON] et al. [151] define SVOCs as presenting in particulate form at a low dilution of emissions corresponding to the conditions under which PM\({}_{2.5}\) emissions are measured in the US emission inventory. This definition has the disadvantage that the definition of SVOCs depends on the emission source, but the authors come to consider that compounds with a volatility less than or equal to \(10^{3}\)\(\upmu\)g m\({}^{-3}\) are SVOCs. Several other C*-based definitions of SVOCs exist in the literature, e.g., C* \(<320\)\(\upmu\)g m\({}^{-3}\)[113]. [PERSON] et al. [151] also introduced the concept of organic compounds with intermediate volatility (IVOCs) (detailed in Section 3.6). Indeed, the authors noticed that there was a \"gap\" between the VOCs identified by gas chromatography-mass spectrometry (GC-MS)--the speciation data for VOC emissions being largely based on this methodology)--with