One of the main night-time oxidants in the atmosphere is the nitrate radical NO3. In the atmosphere NO3 is generated by the reaction (I) between NO2 and ozone O3: NO2 + O3 = NO3 + O2. In its turn, NO3 reacts with different hydrocarbons including the title n-alkanes. The reactions between NO3 and hydrocarbons essentially influence air quality and climate. However, in many cases there is an incomplete understanding of the mechanisms of the reactions between NO3 and volatile organic chemicals. Here we present our results connected with theoretical calculation of the reaction rate constants k describing the interaction of NO3 with C3 –C10 n-alkanes at 298K and 0.1Mpa. In order to do it we have used the following Equation (1), which was received in our work [1]: -lgk = A + B/(Eoxd - Ei) (1) with the newly defined constants A, B, and Eoxd, which equal to 17.5404, 50.9904, and 807.38 kJ/mol respectively. Eq. (1) shows that the specific occupied molecular orbitals SMOs of the studied n-alkanes with the energies Ei play the predominant role in their reactions with NO3. These SMOs include 1s-AO of all the hydrogen atoms of these n-alkanes with one common sign (+ or -) (see [1]). The following Table 1 demonstrates the calculation of the constants k of the given n-alkanes be means of Eq. (1). Table 1. The usage of Eq.(1) for the calculation of k n- Alkane: Ei (kJ/mol) -lgkcalc. -lgkex* Propane 873.56 16.77 16.77* Butane 863.34 16.54 16.63 Pentane 845.16 16.06 16.19 Hexane 841.27 15.96 16.04 Heptane 837.02 15.82 15.82 Octane 835.47 15.72 15.73 Nonane 833.73 15.64 15.61 *The experimental data were taken from [2]. Fig. 1. Formation of three-center C-H-O bonding MO between n-pentane and NO3• radical.