Dasari, S. ; Paris, G. ; Saar, B. ; Pei, Q. ; Cong, Z. ; Widory, D.
Environmental Science & Technology Letters, 2022
`Voir en ligne : https://doi.org/10.1021/acs.estlett.2c00312
Abstract :
Sulfur isotope analysis provides a unique probe for sourcespecific information and certain atmospheric reactions. Globally, atmospheric aerosols in urban locations exhibit significant sulfur mass-independent fractionation (i.e., S-MIF, Δ33S ≠ 0). The origin(s) of these S-MIF anomalies remains unclear, thereby limiting the interpretation and/or application of such signals. Here, we conducted dual-isotope (Δ33S and δ34S) fingerprinting of sulfate aerosols from summertime megacity Delhi in south Asia. A shift toward concomitantly high Δ33S (from 0.2‰ to 0.5‰) and low δ34S (from 5‰ to 1‰) values was observed with the influx of mineral dust. The Fe:Al ratio showed significant correlations with both sulfate loadings (R2 = 0.84) and Δ33S signatures (R2 = 0.77). Contrary to the prevailing paradigm, this observational evidence suggests that mineral-dust-associated sulfate exhibits S-MIF anomalies. Atmospheric processing of mineral dust plausibly leads to the production of these anomalies. Our evaluation suggests that an inherent mechanism(s) remains elusive. Although hindered by end-member uncertainties, we show that S-MIF signals can be source apportioned to quantitatively constrain the fraction of mineraldust-associated sulfate in urban locations. The influx of mineral-dust-associated sulfate can influence urban air pollution affecting air quality and/or human health and as such requires monitoring. Urban Δ33S signals can therefore be used to trace this sulfate fraction, thereby improving our understanding of sulfate aerosol dynamics.