A pathway for production of H₂SO₄ in clouds is by dissolution of SO₂ in cloud droplets followed by reaction of SO₃²⁻ with O₃ (aq):
SO²⁻₃(g) + O₃(aq) → SO²⁻₄ + O₂(aq) (1)
with rate constant k₁ = 1.0 x 10⁹ M⁻¹s⁻¹. relevant equilibria are:
SO₂ (g)⇔ SO₂ . H₂O (2)
SO₂ . H₂O ⇔ HSO⁻₃ + H⁺ (3)
HSO⁻₃ ⇔ SO²⁻₃ + H⁺ (4)
O₃(g) ⇔ O₃(aq) (5)
with equilibrium constants K₁ = 1.2 M atm⁻¹, K₃ = 1.3×10⁻² M, K₄ = 6.3×10⁻⁸ M, K₅ = 1.1×10⁻² M atm⁻¹.

Explain how reaction (5) increases the acidity of the droplet even though Ht does not appear as an explicit product of the reaction.