Abstract
2 min readEight 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 NH 4 + , SO 4 2− , NO 3 − , Ca 2+ , K + , Mg 2+ , 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, NH 4 + and SO 4 2− dominated, with the dust‐derived Ca 2+ contributing nearly equally as SO 4 2− 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, NH 4 + dominated, followed by SO 4 2− , Cl − , Na + , NO 3 − , Ca 2+ , 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 Mg 2+ . In both experiments, NH 4 + , SO 4 2− , NO 3 − , and CO were strongly correlated, indicating that combustion was the dominant source of these species and that NH 3 and other alkaline materials were in sufficient supply to neutralize H 2 SO 4 . The [NH 4 + ] to ([NO 3 − ] + 2[SO 4 2− ]) ratio was ∼0.70 in the two campaigns, with deviations found only in volcano plumes, whereby SO 4 2− was found to correlate with SO 2 . Charge balance of the ions showed both positive and negative deviations whose magnitudes, ∼30%, provide estimates of the lower limits of unmeasured ions. Elevated NO 3 − and Ca 2+ coexist mainly under polluted conditions, suggesting the importance of sequestering HNO 3 by mineral dust.
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