Averaged line profiles of the (1−0) transitions of HCO⁺, HCN, HNC, N₂H⁺, and the (2−1) transition of SiO toward the eastern lobe, the center, and the western lobe of the DR21 Main outflow (see Fig. 1). For HCN and N2H⁺, the velocities corresponding to hyperfine structure components are marked with black ticks. Red dashed lines show the source velocity, −3 km s⁻¹, green dashed lines mark the location of the absorption feature at 9 km s⁻¹, and the gray horizontal lines show the baselines.