WARNING: This page is about a different car, the 2016 Infiniti Q50. However, it is still accessible from the selected car via links, so may be relevant.
The atmospheric pressure sensor is placed at ECM bracket. It detects atmospheric pressure and sends the voltage signal to the ECM.
Courtesy of NISSAN NORTH AMERICA, INC.
The sensor uses a silicon diaphragm which is sensitive to the change in pressure. As the pressure increases, the voltage rises.