Short‐wave radiation balance in an urban aerosol layer

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Abstract
Airborne and ground‐based measurements of incoming and outgoing fluxes of solar radiation were conducted over Hamilton during cloudless periods in July 1973. The urban atmospheric constituents were sufficient to attenuate an extra 10 percent of incoming solar radiation compared to rural and suburban sites. The attenuation of the incoming solar radiation was proportionately matched by changes in the reflected solar radiation such that albedo above the city was constant with height at a value of 0.12. The urban albedo showed a substantial zenith angle dependence. There was a range in absorptionlbackscatter coefficients for different measurement periods but the bulk of the values fell close to the critical ratio (a/b)c which divides the effect of an aerosol between cooling and heating of the Earth‐Atmosphere system. This also predicts an aerosol albedo the same as that at the surface which agrees with the measurements. On a given day a/b decreased with increasing solar zenith angles owing to the relative increase in the backscatter coefficient with greater path length through the aerosol.