Nucleation rate of particles in the lower atmosphere: Estimated time needed to reach pseudo-steady state and sensitivity to H₂SO₄ gas concentration

Using a kinetic model, we estimate the time-needed (t_O) to establish a pseudo-steady state nucleation when sulfuric acid concentration ([H₂SO₄]) suddenly increases to a certain fixed level. We find that t_O is roughly inversely proportional to [H₂SO₄]. The assumption of instantaneously achieved pseudo-steady state concentration of critical clusters, on which the classical nucleation theories are based, is no longer valid when t_O is longer than the time period that [H₂SO₄] can be treated as constant. Under the lower marine atmospheric conditions considered in this study, the nucleation rate predicted by ion-mediated nucleation theory is very sensitive to [H₂SO₄] when [H₂SO₄] is low (<∼7 x 10⁶/cm³) but such a sensitivity reduces significantly as [H₂SO₄] increases, which is quite different from that predicted with classical binary and ternary homogeneous nucleation theories.