Eight inorganic ions in fine aerosol particles (Dp 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 4+> to (3-> + 242->) 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.