Although NOx emission is highly related to the nitrogen content, nitrogen species and redox characteristics of the atmosphere, it increases with increasing combustion temperature. Namely, the unstable volatile-N can be released to emit NOx at a low temperature (700 C), whereas char-N can be released as NOx at a high temperature (900 C) because of the increasing burnout ratio. The insignificant bimodal distribution for the alga En and the unimodal distribution for Ch imply that the volatile-NOx is dominant over the char-NOx and can be partially reduced by the volatile reductants emitted themselves. Particularly, Ch is a type of unicellular algae species that does not contain a large amount of lignin and fibrin, resulting in both easy burnout behavior and almost no char-NOx emission. Sa has considerable volatile- and char-NOx, leading to a bimodal distribution. However, it presents low two-peak concentrations compared with En and Ch because of the low nitrogen content.