The aim of this study was to characterize the carbonaceous aerosol emissions from three types of boilers: pulverized combustion technology boilers (PCBs), circulating fluidized beds (CFBs), and grate boilers (TGBs). These boilers have been used in the industrial district for heating, power, or production, and they have a maximum thermal output range of 7300 MW. The actual particle mass and number concentration and particle size distribution (PSD) were obtained from electrical low-pressure impactor (ELPI) measurements, and a preheated sampling system was used to manage water condensation in the stack gases. The carbonaceous composition of the particles was determined by a thermal-optical analysis. Significant differences were observed in the six boilers with regard to the contribution of carbonaceous fractions to the particle mass and number emissions. The TGBs had much higher carbon aerosol emissions with much higher levels of organic carbon (OC) and elemental carbon (EC), whereas they had higher emissions of total carbon particles, with emission rates that were approximately 15.7 and 10.2 times higher than that of the PCBs and CFBs, respectively. The OC/EC ratio was influenced by the boiler load and fuel type. In all of the boilers, the size distribution of OC and EC displayed a trimodal or bimodal distribution; however, the peaks of different particle sizes were affected by the pollution control device. The percentage of the OC1 + OC2 fraction in the OC was correlated with the temperature of the stack gases, although obvious variations were not observed with the PSD. However, the EC ratio showed variations and size differences, especially in the PM0.1. The char/soot ratio in the PM0.1 was 1.23.9 times that in the PM1, implying that the emission and combustion mechanisms of soot were different from those of char.