An urban solar flux island: Measurements from London

Solar irradiance measurements from a new high density urban network in London are presented. Annual averages demonstrate that central London receives 30 ± 10 W m−2 less solar irradiance than outer London at midday, equivalent to 9 ± 3% less than the London average. Particulate matter and AERONET measurements combined with radiative transfer modelling suggest that the direct aerosol radiative effect could explain 33–40% of the inner London deficit and a further 27–50% could be explained by increased cloud optical depth due to the aerosol indirect effect. These results have implications for solar power generation and urban energy balance models.A new technique using ‘Langley flux gradients’ to infer aerosol column concentrations over clear periods of 3 h has been developed and applied to three case studies. Comparisons with particulate matter measurements across London have been performed and demonstrate that the solar irradiance measurement network is able to detect aerosol distribution across London and transport of a pollution plume out of London.

► New measurements of solar irradiance from a high density urban network in London.
► Central London receives 9 ± 3% less irradiance than the rest of London.
► Inner London deficit plausibly explained by the aerosol direct and indirect effects.
► New technique to infer relative aerosol column concentrations has been developed.
► Solar irradiance network is able to detect aerosol distribution across London.