Many researches reveal human respiratory flow and background ventilation are two important aspects leading to respiratory disease spread. However, current studies on human respiration flows and the resulted exhaled pollutant dispersion are limited, because different head postures, breathing rate and room ventilation can exert profound impact that is not understood very clearly. To evaluate the role of head postures and exhalation rate on transmission of exhaled pollutants, this study adopts a breathing thermal manikin and a computational fluid dynamics (CFD) program to study the exhaled pollutant dispersion from a sitting adult in a room with displacement ventilation. Four different head postures are considered: sitting upright viewing front, sitting upright viewing upward, sitting upright but head turned viewing the lateral and head pillowed on a table. Using carbon dioxide (CO2) as a tracer gas, the impact region of exhaled pollutants under different postures is identified. This study finds out the exhaled pollutant exerts the largest scope when an adult pillows head on the table. If a person makes a deep exhalation and the discharge velocity at nostrils reaches 6.9 m/s, the impacted distance can be as large as 2.0 m.