An automated analyzer to measure surface-atmosphere exchange fluxes of water soluble inorganic aerosol compounds and reactive trace gases

Here, we present a new automated instrument for semicontinuous gradient measurements of water-soluble reactive trace gas species (NH₃, HNO₃, HONO, HCl, and SO₂) and their related aerosol compounds (NH₄⁺, NO₃^-, Cl ^-, SO₄^2-). Gas and aerosol samples are collected simultaneously at two heights using rotating wet-annular denuders and steam-jet aerosol collectors, respectively. Online (real-time) analysis using ion chromatography (IC) for anions and flow injection analysis (FIA) for NH ₄⁺ and NH₃ provide a half-hourly averaged gas and aerosol gradients within each hour. Through the use of syringe pumps, IC preconcentration columns, and high-quality purified water, the system achieves detection limits (3σ-definition) under field conditions of typically: 136/207, 135/114, 29/ 22, 119/92, and 189/159 ng m^-3for NH ₃/NH₄⁺, HNO₃/NO₃ ^-, HONO/ NO₂^-, HCl/Cl^- and SO ₂/SO₄^2-, respectively. The instrument demonstrates very good linearity and accuracy for liquid and selected gas phase calibrations over typical ambient concentration ranges. As shown by examples from field experiments, the instrument provides sufficient precision (3-9%), even at low ambient concentrations, to resolve vertical gradients and calculate surface - atmosphere exchange fluxes under typical meteorological conditions of the atmospheric surface layer using the aerodynamic gradient technique.