Ahvaz, Iran ranks as the most polluted city of the world in terms of PM10 concentrations that lead to deleterious effects on its inhabitants. This study examines diurnal, weekly, monthly and annual fluctuations of PM10 between 2009 and 2014 in Ahvaz. Health effects of PM10 levels are also assessed using the World Health Organization AirQ software. Over the study period, the mean PM10 level in Ahvaz was 249.5 µg m−3, with maximum and minimum values in July (420.5 µg m−3) and January (154.6 µg m−3), respectively. The cumulative diurnal PM10 profile exhibits a dominant peak between 08:00–11:00 (local time) with the lowest levels in the afternoon hours. While weekend PM10 levels are not significantly reduced as compared to weekdays, an anthropogenic signature is instead observed diurnally on weekdays, which exhibit higher PM10 levels between 07:00–17:00 by an average amount of 14.2 µg m−3 as compared to weekend days. PM10 has shown a steady mean-annual decline between 2009 (315.2 µg m−3) and 2014 (143.5 µg m−3). The AirQ model predicts that mortality was a health outcome for a total of 3777 individuals between 2009 and 2014 (i.e., 630 per year). The results of this study motivate more aggressive strategies in Ahvaz and similarly polluted desert cities to reduce the health effects of the enormous ambient aerosol concentrations.

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In this work, ab initio calculations are performed to study chalcogen–chalcogen interactions in binary furan-YHX and thiophene-YHX (X = F, Cl, Br; Y = S, Se) complexes. Interaction energies of these complexes vary between −13.65 and −23.96 kJ mol−1 at MP2/aug-cc-pVTZ level. For a given X, complexes of SeHX have shorter chalcogen–chalcogen distances than SHX counterparts. The strength of the furan-YHX and thiophene-YHX complexes for a given Y decreases as follows: X = F > Cl > Br. Even though chalcogen–chalcogen interactions are mainly dominated by electrostatic effects, interaction energy decomposition analysis shows that polarization and dispersion effects also make important contributions to the stability of these complexes. In addition, charge-transfer from the O(S) lone pair to the σ*Y–X orbital leads to stabilization of these complexes. To further characterize the nature of chalcogen–chalcogen interactions, molecular electrostatic potential and quantum theory of atoms in molecules analyses are performed. Cooperative effects are observed when hydrogen bond and chalcogen–chalcogen interactions coexist in furan-YHF-HCN and thiophene-YHF-HCN.

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