Based on Pearson correlation analysis significance

However, a higher ratio (11.5) was observed in the case of Site C (India) which could be due to either other sources of Cu in the area, or due to differences in the composition of brakes. For the bulk RD, the Cu/Sb ratio was 4.80 ± 0.40 for Delhi and 6.22 ± 3.16 for Birmingham.
Further discussion on elemental ratios is presented in SI.
3.5. Chemical source profiles of the PM10 RD