The London pollution island under Lamb weather types

Abstract

This study considers the daily values of gridded concentrations for NO2, O3, PM10 and PM2.5 in London and its surroundings over 2007–2011. A two-step procedure was used for concentration smoothing to observe the urban pollution island. In the first step, the elliptic fit was compared with fits from the Gaussian and Epanechnikov kernels. The results obtained for the Gaussian kernel were used to apply an elliptic fit and a Gaussian directional fit. Lamb weather types were also determined. As a result, the elliptic fit calculated extended concentrations against those calculated with the kernels, and the Gaussian kernel provided a smoother shape. NO2 and O3 presented the opposite distribution, and the urban pollution island was defined with contrasted concentration values between the city centre and the surrounding areas. The second smoothing simplified the urban shape and determined the background concentrations. The most frequent type was the anticyclonic, although the most contrasting result was obtained for the anticyclonic type with SE flow, since O3 values were low compared to the high NO2 values, thereby revealing pollution transport from the continent under this infrequent type. Finally, the urban pollution island shape is maintained for NO2 and O3 under the most frequent weather types.