An order-of-magnitude calculation of the characteristic time required for the homogeneous heteromolecular nucleation of new stratospheric particles involving the H2SO4-HNO3H20 ternary system is presented. This characteristic time is compared with the characteristic time required for the homogeneous heteromolecular nucleation of sulfuric acid particles involving the H2SO4-H2O binary system and with the characteristic time for the sulfuric acid vapor condensing on the pre-existing particles. From the comparison of these characteristic times, we show that this formation of new particles involving H2SO4-HNO3-H2O may be the most favorable mechanism for the formation of ''sulfuric acid particles'' in the stratosphere.