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abstract
Recent HST and ground-based observations have led to better and new constraints on the properties of Broad Absorption Line (BAL) gas in QSOs in terms of its covering factors, ionization structure, and chemical composition. I present and discuss some of these findings. One of the most important results is that the gas giving rise to BALs has non-uniform ionization and, for often-adopted assumptions about the form of any photoionizing source, likely has very enhanced metal-to-hydrogen abundances relative to solar composition. In particular, the nitrogen abundance relative to other observable metals is enhanced $\approx$ 3 -- 10 times solar values. If normal stellar nucleosynthesis plays a role in producing the metals, this result may be indicative of a relatively flat initial mass function with the nitrogen overabundance produced by secondary processing in massive stars.
