The Environmental Kuznets Curve (EKC) states that societies reverse air pollution once an income threshold is reached, which many scholars seem to read as a universal law. Proponents of the EKC have not explored empirically the conditions and mechanisms underpinning such an expected income-pollution relationship. With a comparative analytical study of the evolution of air pollution in the middle-income countries of Chile and Peru, this paper shows that the way economic development affects environmental quality is conditioned by interplaying ecological, cognitive, and political conditions. The evidence supports the view that income-environment relationships, in general, and air quality turning points, in particular, are influenced by highly idiosyncratic human-ecology context. Thus, income-pollution functional forms should be expected to vary, and to mutate, across time and space.