H₂SO₄‐HNO₃‐H₂O ternary aerosol formation mechanism in the stratosphere

An order‐of‐magnitude calculation of the characteristic time required for the homogeneous heteromolecular nucleation of new stratospheric particles involving the H 2 SO 4 ‐HNO 3 ‐H 2 O 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 H 2 SO 4 ‐H 2 O binary system and with the characteristic time for the sulfuric acid vapor condensing on the preexisting particles. From the comparison of these characteristic times, we show that this formation of new particles involving H 2 SO 4 ‐HNO 3 ‐H 2 O may be the most favorable mechanism for the formation of “sulfuric acid particles” in the stratosphere.