Calibrating Interdependent Photochemistry, Nucleation, and Aerosol Microphysics in Chamber Experiments

Abstract. Laboratory experiments addressing complex phenomena such as atmospheric new-particle formation and growth typically involve numerous instruments measuring a range of key coupled variables. In addition to independent calibration, the combined dataset provides not just constraints on the parameters of interest but also on the critical instrument calibrations. Here we find good agreement between production and loss rates of sulfuric acid (H₂SO₄) in an experiment performed at the CERN CLOUD chamber involving oxidation of sulfur dioxide (SO₂) in the presence of ammonia (NH₃) at 58 % relative humidity, driving new-particle formation and growth of particles by H₂SO₄ + NH₃ nucleation initiated by O₃ photolysis via several light sources. This closure requires consistency across numerous parameters, including: the particle number and size distribution; their condensation sink for H₂SO₄; the particle growth rates; the concentration of H₂SO₄; and the nucleation coefficients for both neutral and ion-induced pathways. Our study shows that accurate agreement can be achieved between production and loss of condensable vapors in laboratory chambers under atmospheric conditions, with accuracy ultimately tied to particle number measurement (i.e. a condensation particle counter). This, in turn implies parameters such as the H₂SO₄ concentration and particle size distributions can be determined to a comparable precision.