RESUMO
The generation of HONO and NO2 by the photolysis of nitrates in the presence of humic acids (HA) was measured under various conditions. The photolysis experiments of HA, KNO3 and KNO3/HA under simulated sunlight was carried out by a flow tube reactor at ambient temperature and pressure. HONO and NO2 were major products by the photolysis of KNO3. By contrast, the photolysis of HA and KNO3/HA mainly generated HONO. HA significantly enhanced the formation of HONO during the photolysis process of KNO3. With increasing the KNO3 mass, the HONO formation rate (RHONO) on KNO3/HA increased while the photolysis rate normalized by the KNO3 mass exhibited an opposite trend. RHONO on KNO3/HA linearly increased with irradiation intensity (88-262â¯W/m2) and relative humidity (7-70%), whereas it linearly decreased with the pH (pHâ¯=â¯2-12). In addition, the reaction paths of the HONO formation by the photolysis of nitrates in the presence of HA were proposed according to experimental results. Finally, atmospheric implications of the enhanced HONO formation by the photolysis of nitrates in the presence of HA were discussed.
Assuntos
Substâncias Húmicas , Dióxido de Nitrogênio/síntese química , Ácido Nitroso/síntese química , Fotólise , Poluentes Atmosféricos/química , Concentração de Íons de Hidrogênio , Nitratos/química , Compostos de Potássio/química , Luz SolarRESUMO
Calculations were performed to determine the structures, energetics, and spectroscopy of the atmospherically relevant complexes (HNO(3)).(NO(2)), (HNO(3)).(N(2)O(4)), (NO(3)(-)).(NO(2)), and (NO(3)(-)).(N(2)O(4)). The binding energies indicate that three of the four complexes are quite stable, with the most stable (NO(3)(-)).(N(2)O(4)) possessing binding energy of almost -14 kcal mol(-1). Vibrational frequencies were calculated for use in detecting the complexes by infrared and Raman spectroscopy. An ATR-FTIR experiment showed features at 1632 and 1602 cm(-1) that are attributed to NO(2) complexed to NO(3)(-) and HNO(3), respectively. The electronic states of (HNO(3)).(N(2)O(4)) and (NO(3)(-)).(N(2)O(4)) were investigated using an excited state method and it was determined that both complexes possess one low-lying excited state that is accessible through absorption of visible radiation. Evidence for the existence of (NO(3)(-)).(N(2)O(4)) was obtained from UV/vis absorption spectra of N(2)O(4) in concentrated HNO(3), which show a band at 320 nm that is blue shifted by 20 nm relative to what is observed for N(2)O(4) dissolved in organic solvents. Finally, hydrogen transfer reactions within the (HNO(3)).(NO(2)) and (HNO(3)).(N(2)O(4)) complexes leading to the formation of HONO, were investigated. In both systems the calculated potential profiles rule out a thermal mechanism, but indicate the reaction could take place following the absorption of visible radiation. We propose that these complexes are potentially important in the thermal and photochemical production of HONO observed in previous laboratory and field studies.
Assuntos
Nitratos/química , Ácido Nítrico/química , Nitritos/química , Dióxido de Nitrogênio/química , Óxidos de Nitrogênio/química , Ácido Nitroso/síntese química , Poluentes Atmosféricos/química , Atmosfera , Simulação por Computador , Modelos Químicos , Ácido Nitroso/química , Espectrofotometria Infravermelho/métodos , Espectrofotometria Ultravioleta/métodos , Análise Espectral Raman/métodos , Propriedades de SuperfícieRESUMO
A simple and speedy procedure is described for the preparation and application of nitrous acid in mutagenic experiments. The conventional incubation mixture of sodium nitrite solution with acetate buffer is replaced by an aqueous solution of nitrous acid prepared by running a solution of sodium nitrite through a column of ion exchange. The procedure eliminates also the interference of other substances. Experimental appraisal of the technique was done during the mutagenic improval of the fungus Claviceps purpurea.