Upper left corner: model flux ratios between Paβ and Paγ (y-axis) versus n_H (x-axis), compared with the observed flux ratio and error bars (horizontal lines). All other panels: model flux ratios of studied atomic lines relative to Paγ (y-axis) versus elemental abundance relative to H in solar units (x-axis) for all elements in this study. The diagonal dashed lines indicate the systematic error in the models due to the charge exchange rate coefficients, as is discussed in Appendix B. Observational flux ratios are indicated (horizontal lines) with error bars for the four elements with > 3σ detections (C, O, S, and Ca), while the 3σ upper limits are indicated for the other elements.