High arsenic (As) groundwater is frequently found in inland basins, yet the contributions of different processes to aqueous As distributions remain unresolved. In the Hetao Basin, a typical inland basin, groundwater As concentrations generally increased from the alluvial fan through the transition area to the flat plain. A geochemical process‐based reactive transport model was established to evaluate and quantify the processes of As mobilization in the northwestern Hetao Basin. Thirty‐six groundwater samples and eight sediment samples were collected from the alluvial fan to the flat plain to investigate the geochemical characteristics of the groundwater system. Along the approximate flow path, groundwater evolved from oxic‐suboxic conditions to anoxic conditions, with increasing concentrations of As, Fe (II), and NH4+, and decreasing Eh and SO42−/Cl−. Modeling results indicated that the observed concentrations of Fe (II) were caused by reductive dissolution of Fe (III) oxides and subsequent precipitation of mackinawite and siderite. Reductive dissolution of Fe (III) oxides was primarily driven by organic matter degradation (>75%), followed by H2S oxidation (<25%). More As was sequestered by mackinawite precipitation and adsorption than that released via abiotic reduction of Fe (III) oxides by H2S. Reductive dissolution of Fe (III) oxides was the dominant mechanism for liberating As in both the transition area and the flat plain (>70%), and As desorption under elevated pH and competitive adsorption by HCO3− and PO43− made an important contribution to As enrichment (up to 30%). Overall, this study provides an insight into the relative contributions of different geochemical processes to As enrichment in inland basins.

Abstract. Variations of total column CO and O 3 in the atmosphere over the epicenter areas of 35 great earthquakes that occurred throughout the world in recent years were studied based on the hyper-spectrum data from Atmospheric Infrared Sounder (AIRS). It was found that anomalous increases of CO and/or O 3 concentrations occurred over the epicenter areas of 12 earthquakes among the 35 studied ones. However, increases in both CO and O 3 concentrations were found for 6 earthquakes. The O 3 anomalies appeared in the month when the earthquake occurred and lasted for a few months, whereas CO anomalies occurred irregularly. The duration of CO and O 3 anomalies related to the earthquakes ranged from 1 to 6 months. The anomalies of CO concentration related to the earthquake can be mainly attributed to gas emission from the lithosphere and photochemical reaction, while the anomalous increases in O 3 concentration can be mainly due to the transport of O 3 -enriched air and photochemical reaction. However, more work needs to be done in order to understand the mechanism of the CO and O 3 anomalies further.