Despite the differences in model parameterisation and distance-decay functions, however, measurement studies have also shown that the correlation between noise and air pollutants are moderate overall, which supports the findings of our study. Kheirbek et al. (2014) found moderate correlations for NO2 (Pearson's r = 0.6–0.7) and PM2.5 (r = 0.45–0.51) and selected noise metrics across 56 sampling sites in New York City. Foraster et al. (2011) also found moderate correlations (Pearson's r = 0.62) between measured NO2 concentrations and modelled noise levels (A-weighted long-term average sound level for 24 h) across 83 sites in the Spanish city of Gerona. These are of similar magnitude to correlations found between NO2 and 5-min A-weighted equivalent continuous sound pressure levels (Leq,5 min) measurements in Vancouver (Davies et al., 2009). A study conducted in two US cities (Chicago and Riverside) observed slightly lower correlations between 151 measurements of Leq,5 min and NO2 (r = 0.38 and 0.46, respectively) (Allen et al., 2009).