Most of the organic molecules and dust in the ISM are produced in the final phases of stellar evolution of low- and intermediate-mass stars, from the Asymptotic Giant Branch (AGB) to planetary nebulae (PNe). These stars are sources of such carbonaceous species as polycyclic aromatic hydrocarbons (PAHs), which are ubiquitous in the Universe, and fullerenes (e.g. C60), the largest molecules found in Space. Studies of PNe in irregular galaxies in the Local Group (mostly focused on the LMC and SMC) have revealed a diverse spectral zoo with rich carbon-dominated chemistry. Tracing the dust evolution with metallicity of these irregular galaxies is, however, not optimal because of their complex star-forming histories. With its metallicity gradient, the Milky Way is an ideal laboratory to investigate these effects. In particular, the metal-poor outer regions of the Milky Way are largely unexplored.

I will present a spectroscopic study of the dust composition in 23 PNe in the Galactic anti-centre using data from the Spitzer Space Telescope. It is found that about 75% of the sample shows carbon-rich dust emission, which supports the notion that low metallicity favours carbon-rich dust production by AGB stars. Three of these sources contain C60, one of which is a new detection, and four contain silicon carbide, a feature that is rare in the Milky Way but more common in the Magellanic Clouds. This shows that there are many similarities between the dust emission observed in this sample with that in the metal-poor LMC and SMC.