<p>Comprehensive experiments were undertaken utilizing a low-output stationary diesel engine at six engine-operating loads to investigate profiles of size-segregated particulate fractions, namely organic carbon (OC) and elemental carbon (EC) (OC1, OC2, OC3, OC4, optical pyrolysis (OP), EC1, EC2, EC2, and EC3). Assessments of OC and EC emissions and the associated human health impacts arising through deposition in lungs were conducted to elucidate cause-effect relationships. The percentage contribution of OC to total carbon (TC) mass was higher than that of EC at lower engine-operating load, whereas this contribution was lower than that of EC at higher engine-operating load. From the mass closure, it was observed that the highest mass contribution to TC was acquired by EC1 sub-fraction followed by EC2 sub-fraction. The mass contribution of three sub-fractions of EC (EC1, EC2 and EC3) increased with a rise in engine-operating load. The sub-fractions OC and EC were observed to be more populated in the submicron range. The estimated values of total respiratory deposition dose (RDD) of OC and EC increased with rise in engine-operating load for fine, submicron and ultrafine particles. The ultrafine carbonaceous particles could penetrate more into deepest parts of the respiratory tract compared to submicron, fine and PM₁₀ particles. Various sets of observations through RDD in human lungs from this study underscore the critical significance of addressing particulate carbon emissions from the stationary diesel engines used for power generation with a human health perspective.</p>