Review and comparative analysis of the particulate matter generated in conventional cigarettes and heated tobacco products - mainstream and environmental emissions

•Environmental air quality implies evaluating particulate matter from tobacco.•Ultrafine particles isolated both for cigarettes and HNBPs.•Around 50 mg of TPM /stick are collected in the mainstream.•Indoor PM, μg/m3: 100-500 cig, 1.4-15.5 HNBP, 1.3-14.7 background.•Cigarette smoking implies 3-6 times more particles than the use of HNBPs.•Higher volatility of the particulate matter in the aerosol from HNBPs. This study aims to revise and compare published data devoted to the identification, characterization, and quantification of suspended particulate matter (PM) in the smoke from combustible cigarettes or the aerosol from heat-not-burn products (HNBP), analyzing mainstream and indoor scenarios. It has been motivated by the difficulty of a proper comparison from the published data, mostly due to the very different experimental conditions used in each published study, often even not clearly indicated. Despite the difficulty in a straightforward comparison, important differences in the particulate matter present in the smoke from combustible cigarettes and the aerosols from HNBPs have been confirmed. In general, the concentration of particulate matter in the aerosol emitted by HNBPs is much lower than in the cigarette smoke. However, in the mainstream, ultrafine particulate matter has been isolated both for combustible cigarettes and HNBPs, and the Total Particulate Matter (TPM) collected is in the same range, around 50 mg/stick, slightly higher for HNBPs. The indoor concentration of PM usually ranges from 100-500 μg/m3 for combustible cigarettes, 1-2 orders of magnitude higher than the present in background air (1.3-14.7 μg/m3), whereas for HNBPs it ranges from 1.4-15.5 μg/m3, which is similar to the background. Indoors, the number of particles generated from cigarette smoking is much larger than those from the use of HNBPs in a factor of 3-6. Nevertheless, the mean particle sizes and particulate composition are among the main differences between cigarette smoke and HNBP aerosols. The mean particle sizes are larger in the smoke from combustible cigarettes and contain black carbon particles (soot), whereas the particulate matter from HNBPs presents a smaller size, is predominantly liquid-based, and is much more volatile. [Display omitted]