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Spectral observations of Neptune made in 2019 with the MUSE instrument at theVery Large Telescope in Chile have been analysed to determine the spatialvariation of aerosol scattering properties and methane abundance in Neptune'satmosphere. The darkening of the South Polar Wave (SPW) at $\sim$ 60$^\circ$S,and dark spots such as the Voyager 2 Great Dark Spot is concluded to be due toa spectrally-dependent darkening ($\lambda < 650$nm) of particles in a deepaerosol layer at $\sim$ 5 bar and presumed to be composed of a mixture ofphotochemically-generated haze and H$_2$S ice. We also note a regularlatitudinal variation of reflectivity at wavelengths of very low methaneabsorption longer than $\sim$ 650 nm, with bright zones latitudinally separatedby $\sim$ 25$^\circ$. This feature, similar to the spectral characteristics ofa discrete deep bright spot DBS-2019 found in our data, is found to beconsistent with a brightening of the particles in the same $\sim$5-bar aerosollayer at $\lambda > 650 $ nm. We find the properties of an overlyingmethane/haze aerosol layer at $\sim$ 2 bar are, to first-order, invariant withlatitude, while variations in the opacity of an upper tropospheric haze layerreproduce the observed reflectivity at methane-absorbing wavelengths, withhigher abundances found at the equator and also in a narrow `zone' at$80^\circ$S. Finally, we find the mean abundance of methane below itscondensation level to be 6--7% at the equator reducing to $\sim$3% south of$\sim$25$^\circ$S, although the absolute abundances are model dependent.

Latitudinal variations in methane abundance, aerosol opacity and aerosol scattering efficiency in Neptune's atmosphere determined from VLT/MUSE