Enrichment of 13C in diacids and related compounds during photochemical processing of aqueous aerosols: New proxy for organic aerosols aging

To investigate the applicability of compound specific stable carbon isotope ratios (delta C-13) of organics in assessment of their photochemical aging in the atmosphere, batch UV irradiation experiments were conducted on two ambient (anthropogenic and biogenic) aerosol samples in aqueous phase for 0.5-120 h. The irradiated samples were analyzed for delta C-13 of diacids, glyoxylic acid (omega C-2) and glyoxal. delta C-13 of diacids and related compounds became larger with irradiation time (i.e., aging), except for few cases. In general, delta C-13 of C-2-C-4 diacids showed an increasing trend with decreasing chain length. Based on delta C-13 of diacids and related compounds and their relations to their concentrations, we found that C-2 and C-3 are enriched with C-13 during the photochemical decomposition and production from their higher homologues and oxoacids. Photochemical breakdown of higher (>= C-3) to lower diacids is also important in the enrichment of C-13 in C3-C9 diacids whereas their production from primary precursors causes depletion of C-13. In case of omega C-2 and glyoxal, their photochemical production and further oxidation to highly oxygenated compounds both cause the enrichment of C-13. This study reveals that delta C-13 of diacids and related compounds can be used as a proxy to trace the aging of organic aerosols during long-range atmospheric transport

Distribution, mobility, and pollution assessment of Cd, Cu, Ni, Pb, Zn, and Fe in intertidal surface sediments of Sg. Puloh mangrove estuary, Malaysia

Sungai Puloh mangrove estuary supports a large diversity of macrobenthic organisms and provides social benefits to the local community. Recently, it became a major recipient of heavy metals originating from industries in the hinterland as a result of industrialization and urbanization. This study was conducted to evaluate mobility and pollution status of heavy metals (Cd, Cu, Ni, Pb, Zn, and Fe) in intertidal surface sediments of this area. Surface sediment samples were collected based on four different anthropogenic sources. Metals concentrations were analyzed using an atomic absorption spectrophotometer (AAS). Results revealed that the mean concentrations were Zn (1023.68 ± 762.93 μg/g), Pb (78.8 ± 49.61 μg/g), Cu (46.89 ± 43.79 μg/g), Ni (35.54 ± 10.75 μg/g), Cd (0.94 ± 0.29 μg/g), and Fe (7.14 ± 0.94 %). Most of the mean values of analyzed metals were below both the interim sediment quality guidelines (ISQG-low and ISQG-high), except for Pb concentration (above ISQG-low) and Zn concentration (above ISQG-high), thus suggesting that Pb and Zn may pose some environmental concern. Cadmium, Pb, and Zn concentrations were above the threshold effect level (TEL), indicating seldom adverse effect of these metals on macrobenthic organisms. Pollution load index (PLI) indicated deterioration and other indices revealed the intertidal surface sediment is moderately polluted with Cd, Pb, and Zn. Therefore, this mangrove area requires urgent attention to mitigate further contamination. Finally, this study will contribute to data sources for Malaysia in establishing her own ISQG since it is a baseline study with detailed contamination assessment indices for surface sediment of intertidal mangrove area