Possible ear infection.

My dog has had this black mass area on his ear for some time now. He is a pug so has a history of ear infections 

Hello - I am not sure that I can make out one specific black mass here - it is a limitation of photography.  The folds of some pugs' ears are quite densely packed and it is difficult to tell tumour from polyp from severe allergy, from yeast infection, from underlying hypothyroidism, from ibflammation at this angle.  Tests may be needed.  Your vet would want to examine this ear in context in real life, to see how the patient is overall and how the apparent folds attach lower down the canal.  However, you do say something that reflects badly on veterinary / dog-breeding society:  the suggestion that this is a pug, so he therefore has ear infections.  Surely, if a feature has been bred into a dog such that ear infections (that's a misnoma - not always 'infections' in the true medical sense - often 'inflammations') are regarded as normal, this raises massive animal wealfare concerns and should prompt calls to change the way in which those animals are bred.  To breed an animal, assuming that they will inherit certain medical problems, is a huge concern that we as a nation, have not done as much to avoid as we should have.  Whether or not problems of breeding relate to your own pugs' case, is impossible for me to know from here and also beside the point, but I hope that your vet can help you to find and treat the specific problem.   Often with pugs, ear problems become chronic - as in, they recurr on an ongoing basis, so if this turns out to be a typical 'pug ear,' there's a solid chance that follow-up treatment may be needed.

Indeed, it is best to think of ears as part of the skin - which just happens to be out of reach down a hole.  Skin and ear problems are often lifelong and need to be 'managed' rather than 'treated.'  However, I am generalising again and your vet will discuss this specific case in more detail, as it may be different.

Wishing your boy a more comfortable ear very soon.