The 5200-¿ N I (4S-2D) emission monitored by the visible airglow experiments on Atmosphere Explorer C and D combined with simultaneous measurements of atmospheric composition yields the following results. The metastable 2D term of atomic nitrogen must be produced in the F region at near the maximum rate allowed by currently accepted chemistry. The rate coefficient deduced for the loss of N(2D) by reaction with O2 is in good agreement with the laboratory result. The quenching rate of N(2D) by electron lies in the range 3.6--6.5¿10-10(Te/300)1/2 cm3 s-1 if the laboratory rate for N2+ recombination is applicable to the thermosphere. The value may be somewhat larger than this if nonthermal effects are important. The quenching rate by atomic oxygen is near 4¿10-13 cm3 s-1, much smaller than the laboratory value.