A note on unusual Si/Al ratios in PM₁₀ and PM_2.5 road dust at several locations in India

The Si/Al ratios in road dust (PM₁₀ and/or PM_2.5) at several locations in India were examined and found to range between 1.6 and 84.9. The potential factors for this wide range of unusual Si/Al ratios in road dust are not known at this time. In addition to re-assessing data quality, the observations suggest the need to carefully quantify anthropogenic inputs of these elements to road dust. The findings of this study also contradict popular assumptions about minimal enrichment of crustal elements by anthropogenic sources and highlight the need to re-visit dust mass estimation using Si and Al as a surrogate. Further, characterization of Si/Al ratio in road dust at locations in India and the influence of local geology/geochemistry on it are especially important, if this ratio is to be used either for dust estimation or as an input to ambient aerosol mass source apportionment models.