Fit of a range of η models to the HARPS transmission spectra of HD 189733b. The data and models are binned by 20× (panel a)), 5× (panel b)) and 2× (panels c) and d)). Models correspond to those described in Table 5. Some additional models (2100 K, 2600 K, 3100 K, the hottest in panels a) and b) and the continuum level (in red), which correspond to the altitudes of a haze layer deck, are also shown for comparison. Our analysis shows that the atmosphere of HD 189733b is not isothermal.