Airborne measurement of inorganic ionic components of fine aerosol particles using the particle-into-liquid sampler coupled to ion chromatography technique during ACE-Asia and TRACE-P

[1] Eight inorganic ions in fine aerosol particles (D_p < 1.3 μm) were measured on board the NCAR C130 and NASA P-3B aircraft during the 2001 Aerosol Characterization Experiment (ACE)-Asia and the Transport and Chemical Evolution over the Pacific (TRACE-P) experiments, respectively. Concentrations of NH₄⁺, SO₄²⁻, NO₃⁻, Ca²⁺, K⁺, Mg²⁺, Na⁺, and Cl⁻ were determined using a particle-into-liquid sampler coupled to ion chromatography (PILS-IC) technique at a 4-min resolution and a limit of detection <0.05 μg m⁻³. The maximum total ion concentrations observed on the C130 and the P-3B were 27 μg m⁻³ and 84 μg m⁻³, respectively. During ACE-Asia, NH₄⁺ and SO₄²⁻ dominated, with the dust-derived Ca²⁺ contributing nearly equally as SO₄²⁻ in mixing ratios. The sea-salt-derived Na⁺ and Cl⁻ were comparable to biomass-burning tracer K⁺, showing >1 ppbv only in the top 1% sample population. During TRACE-P, NH₄⁺ dominated, followed by SO₄²⁻, Cl⁻, Na⁺, NO₃⁻, Ca²⁺, and K⁺, in decreasing order of importance. In addition to a sea-salt origin, Cl⁻ showed a source in urban emissions possibly related to biofuel combustion. Both sea salt and dust contributed to Mg²⁺. In both experiments, NH₄⁺, SO₄²⁻, NO₃⁻, and CO were strongly correlated, indicating that combustion was the dominant source of these species and that NH₃ and other alkaline materials were in sufficient supply to neutralize H₂SO₄. The [NH₄⁺] to ([NO₃⁻] + 2[SO₄²⁻]) ratio was ∼0.70 in the two campaigns, with deviations found only in volcano plumes, whereby SO₄²⁻ was found to correlate with SO₂. Charge balance of the ions showed both positive and negative deviations whose magnitudes, ∼30%, provide estimates of the lower limits of unmeasured ions. Elevated NO₃⁻ and Ca²⁺ coexist mainly under polluted conditions, suggesting the importance of sequestering HNO₃ by mineral dust.