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

Eight inorganic ions in fine aerosol particles (D-p < 1.3 mm) 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 mu g m(-3). The maximum total ion concentrations observed on the C130 and the P-3B were 27 mu g m(-3) and 84 mu g 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 similar to0.70 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, similar to30%, 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.