Across all London postcodes, we observed overall moderate correlations between modelled noise and air pollution
that were stable over time (Spearman's rho range: |0.34–0.55|). Correlations, however, varied considerably
depending on the spatial unit: largest ranges were seen in neighbourhoods and 1 km grid squares (both
Spearman's rho range: |0.01–0.87|) and was less for Boroughs (Spearman's rho range: |0.21–0.78|). There was
little difference in correlations between exposure tertiles, distance from road or deprivation tertiles.
Associations between noise and air pollution at the relevant geographical unit of analysis need to be carefully
considered in any epidemiological analysis, in particular in complex urban areas. Low correlations near roads,
however, suggest that independent effects of road noise and traffic-related air pollution can be reliably determined
within London