Characteristic Solutes in Geothermal Water from the Rehai Hydrothermal System,Southwestern China

Rehai, a high-temperature hydrothermal system located in the southern part of the Tengchong volcanic geothermal area of Yunnan Province, is characterized by intensive hydrothermal activities. The hot springs at Rehai that have been sampled so far are Na-HCO3-Cl or Na-HCO3 springs except for the one at Diretiyanqu （experience geothermal area） which is an acid sulfate spring. As typical characteristic solution constituents in high-temperature hydrothermal systems with magma as heat source, CI, B and As in the Rehai geothermal waters originate mainly from the addition of magmatic fluid. However, both the mixing of magmatic fluid and the dissolution of reservoir hostrocks contribute to the enrichment of fluoride in the Rehai geothermal waters, although their fluoride concentrations are primarily controlled by the solubility of fluorite as indicated by a clear negative relation between solution fluoride and calcium concentrations. The much higher concentration of SO4^2- in the Diretiyanqu Spring as compared to the other springs outcropping at Rehai implies a quite different geochemical genesis for this spring. The H2S-rich vapor, separated from the deep geothermal fluid during boiling process （i.e., adiabatic cooling）, can ascend to shallow aquifers where it is mixed with cold groundwaters and oxidized. Acid sulfate-rich hot springs are generally formed in this manner although only one spring of this type has been samnled during the field investigation of this studv.

Research progress on secondary formation,photosensitive reaction mechanism and human health effects of chromophoric brown carbon

Brown carbon(BrC)has attracted widespread attention because of its strong absorption of solar radiation in the ultraviolet-visible wavelength range,which causes adverse impacts on human health.Originally,BrC was a physically defined class of substances.However,current research has gradually shifted towards the identification of its chemical groups,because its light-absorbing capability,chemical properties and health effects mainly depend on the chemical composition of its chromophores.Therefore,this review mainly focuses on the chemical understanding of BrC based on chromophores,and the secondary formation mechanism of chromophores,photosensitized reactions,and human health effects of BrC were detailly summarized.Firstly,BrC chromophores are divided into five categories:nitrogen-heterocycles,nitrogen-chain,aromatic species,oligomers and sulfur-containing organic compounds.Different chromophore precursor species exhibit variations,and their formation mechanisms are also distinct.Secondly,BrC can trigger the production of secondary organic aerosol(SOA)precursors or cause SOA growth because BrC is an important component of light-absorbing particles formed during incomplete combustion of biomass and fossil fuels,potentially exerting adverse effects on human health.Finally,developing sufficiently separated methods for BrC and refining algorithms and machine learning can lead to a more effective understanding of the chemical composition of chromophores,thus enabling better evaluation of the atmospheric effects and health impacts of BrC.In all,this review provides new insights into the categories of BrC chromophores and new advance in secondary formation mechanisms,photosensitized reactions,and human health effects on the basis of chemical structures.