Depending on what you are considering as air quality, and if you also consider water/ground quality risks too? Landfills produce a large amount of methane which not good on greenhouse gases, as well as providing a large amount of leachate risk. This is compared to the much lower land use and Waste to Energy production capacity which incinerator provide, while also having some emissions, particulate, and ash disposal issues.

So if you are a big city or Island without enough land and enough budget to build a facilite to mitigate the negatives (San Francisco, Hawaii, Washington DC, New York, Boston, etc), then incineration begins to make sense if you can mitigate the negatives to a high enough degree. Islands can indeed have to do it as there is just no viable alternative. It can be incredibly well used to as the Shetlands have a WTE which also uses waste energy to heat homes and buildings replacing home furnaces and being more efficient.