I'm overhauling a project I've been working half-arsed on for a long time, and I want to make it alien. I'm considering ammonia-based respiration (nitrification) in a reasonably ammonia-rich atmosphere. I know little about biochemistry though. I'm quite confused and perhaps I'm horribly oversimplifying everything. Prepare for a barrage of questions (sorry).

I'm pretty much basing everything on what's written here.

1. Ammonia is not very dense. Would it all just escape higher up into the atmosphere, except where dissolved in rivers, lakes and seas? Will a slightly higher gravity help at all by pulling the atmosphere in or will there just be more collected material in the atmosphere?

2. I'm looking at using SH2 (hydrogen sulphide) as a reducing agent. Therefore, there should be sulphur ions produced assuming the hydrogen is taken by the oxygen. I'm assuming this sulphur would then react with oxygen to produce SO2. This releases quite a lot of energy, reacting explosively in air, according to wikipedia. Would this still be dangerous if diluted? Could it cause harm? Is there even a way the energy release could be harnessed?

3. Would I be right to assume the reaction can be reversed with some external energy input, photosynthesis style? Would the strong bonds in SO2 pose an issue here? Would photosynthesis reverse both steps in one go?

4. Strangely, ammonia is an inhibitor of nitrification, apparently, as is nitric acid which may be produced. Would this affect the viability of its widespread use? The world I'm 'building' is a little warmer than Earth by 30^o C or so, which means metabolisms will be a bit higher. Will this help to much of an extent?

5. What happens to the nitrate and hydrogen ion produced? Is the hydrogen 'used up' in ATP production (or equivalent - I'll cross that bridge when I get to it some other time)? Or is nitric acid formed? Would it remain dissolved until excreted/removed without causing problems or would there be acidity-based repercussions?

6. If I have all of this wrong, what would be a suitable electron donor?