Formation of HONO from the NH3-promoted hydrolysis of NO2dimers in the atmosphere
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Significance As the primary source of “detergent” OH radicals, nitrous acid (HONO) plays an essential role in the chemistry of the atmosphere. Despite extensive studies, the source of HONO is still elusive. Although recent studies have shown the importance of reactive nitrogen compounds during aerosol formation, mechanistic insight into how these compounds react is still missing. Herein, based on Born–Oppenheimer molecular-dynamics simulations and free-energy sampling, we identified a formation mechanism for HONO via the NH 3 -promoted hydrolysis of NO 2 dimer (ONONO 2 ) on water clusters/droplets. The near-spontaneous formation of HONO at the water–air interface sheds light on the catalytic role of water droplets in atmospheric chemistry. This finding provides not only a missing HONO source but also insight into HONO chemistry.Keywords:
Nitrous acid
Atmospheric chemistry
Previous observations that the nitrous acid-catalysed nitration of p-nitrophenol in aqueous nitric acid becomes zeroth-order with respect to nitrous acid as the concentration of nitrous acid is increased have been confirmed. However, under these conditions, the reaction is shown to remain first-order with respect to p-nitrophenol. This observation, and studies of the u.v. spectra of related solutions, rule out the previously suggested interpretation involving the formation of a high concentration of p-nitrophenyl nitrite in solution. Observations on the kinetic form of the reaction and on the variation of the reaction rate with the concentration of nitric acid in media of constant H0 are shown to be consistent with a reaction in which the p-nitrophenoxide ion is oxidised to the p-nitrophenoxyl radical which then reacts with nitrogen dioxide.
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Nitrogen dioxide
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Nitrous acid
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Atmospheric chemistry
Nitrogen oxides
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Introduction The corrosive attack of nitric acid on copper is mainly due to the nitrous acid formed by the reaction between copper and nitric acid. The reaction is conditioned by: the concentration of the acid; temperature; the presence of nitrous acid; and the solubility of the reaction products in the acid. It has been suggested that as soon as a trace of NO2 has been formed by the reaction, NO3− + 2H+ + e → NO2 + H2O, it is quickly reduced to NO2− by the reaction NO2 + e → NO2−. Then NO2− combines with hydrogen ions to give nitrous acid. Nitrous acid can readily react with nitric acid to regenerate twice the original quantity of NO2 by the reaction, HNO2 + HNO3 → 2NO2 + H2O. In each cycle the quantity of NO2 and HNO2 is doubled.
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Gaseous nitrous acid (HONO) is a critical source of hydroxyl radicals (OH) in the troposphere. While both direct and secondary sources contribute to atmospheric HONO, direct emissions have traditionally been considered minor contributors. In this study, we developed δ 15 N and δ 18 O isotopic fingerprints to identify six direct HONO emission sources and conducted a 1-y case study on the isotopic composition of atmospheric HONO at rural and urban sites. Interestingly, we identified that livestock farming is a previously overlooked direct source of HONO and determined its HONO to ammonia (NH 3 ) emission ratio. Additionally, our results revealed that spatial and temporal variations in atmospheric HONO isotopic composition can be partially attributed to direct emissions. Through a detailed HONO budget analysis incorporating agricultural sources, we found that direct HONO emissions accounted for 39~45% of HONO production in rural areas across different seasons. The findings were further confirmed by chemistry transport model simulations, highlighting the significance of direct HONO emissions and their impact on air quality in the North China Plain. These findings provide compelling evidence that direct HONO emissions play a more substantial role in contributing to atmospheric HONO than previously believed. Moreover, the δ 15 N and δ 18 O isotopic fingerprints developed in this study may serve as a valuable tool for further research on the atmospheric chemistry of reactive nitrogen gases.
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Nitrous oxide
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The kinetics of the reaction of nitrous acd with n-butylaldehyde and neptunium(Ⅵ)is studied and the results in different reaction systems are obained:(1)in system of nitrous acid withn-butylaldehyde,when t=20℃ and ion strengh I=2.0mol/kg,the rate constant k_1=0.761￣2/(mol￣2·min );(2) in system of nitrous acid withNp(Ⅵ),when and I=1.0mol/kg,theapparent rate constant;(3)in system of nitrous acid and n-butylaldehydewith Np(Ⅵ),when and I=1.0mol/kg,the apparent rate constant .The results show that the nitrous acid has abigger reaction rate with Np(Ⅵ)than with n-butylaldehyde or n-butylaldehyde with Np(Ⅵ).
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The oxidation of U(Ⅳ)by nitrous acid in the present of plutonium was studied.The influence of the concentration of nitrous acid,nitric acid,plutonium on the oxidation of U(Ⅳ)was investigated.The results show that plutonium can catalyze the reaction between U(Ⅳ)and nitrous acid.And the rate equation of the reaction between U(Ⅳ)and nitrous acid catalyzed by plutonium was obtained:-dc(U(Ⅳ))/dt=kc(U(Ⅳ))c1.3(HNO3)c1.3(NO-2),k=(0.69±0.04)L2.6/(mol 2.6·min)when the temperature was 29℃.The mechanism of the oxidation of U(Ⅳ)was discussed.
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Abstract Nitrous acid (HONO) is an important radical precursor that can impact secondary pollutant levels, especially in urban environments. Due to uncertainties in its heterogeneous formation mechanisms, models often under predict HONO concentrations. A number of heterogeneous sources at the ground have been proposed but there is no consensus about which play a significant role in the urban boundary layer. We present a new one‐dimensional chemistry and transport model which performs surface chemistry based on molecular collisions and chemical conversion, allowing us to add detailed HONO formation chemistry at the ground. We conducted model runs for the 2010 CalNex campaign, finding good agreement with observations for key species such as O 3 , NO x , and HO x . With the ground sources implemented, the model captures the diurnal and vertical profile of the HONO observations. Primary HO x production from HONO photolysis is 2–3 times more important than O 3 or HCHO photolysis at mid‐day, below 10 m. The HONO concentration, and its contribution to HO x , decreases quickly with altitude. Heterogeneous chemistry at the ground provided a HONO source of 2.5 × 10 11 molecules cm −2 s −1 during the day and 5 × 10 10 molecules cm −2 s −1 at night. The night time source was dominated by NO 2 hydrolysis. During the day, photolysis of surface HNO 3 /nitrate contributed 45%–60% and photo‐enhanced conversion of NO 2 contributed 20%–45%. Sensitivity studies addressing the uncertainties in both photolytic mechanisms show that, while the relative contribution of either source can vary, HNO 3 /nitrate is required to produce a surface HONO source that is strong enough to explain observations.
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Atmospheric chemistry
Chemical Transport Model
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In this study, a monoethanolamine aerosol growth model was developed to investigate the aerosol growth factor. Interactions among the internal conditions in an absorber were considered in this aerosol model. Additionally, an experiment was conducted to measure aerosol particle size, for collecting in-house validation data. Sucrose was used as the aerosol nuclei instead of sulfuric acid to prevent the corrosion of equipment used in the experiment. Experimental results showed that the outlet aerosol sizes increased to the same size regardless of the sucrose concentrations. The aerosol growth model was validated using the in-house experimental data. The aerosol growth model efficiently predicted the aerosol size. For investigating aerosol growth effects, particle number concentration was determined to be the primary factor affecting aerosol growth and amine emissions. When the particle number concentration increased, the aerosol size decreased, whereas the MEA emission increased.
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The nitrous acid catalysed nitration of 4-nitrophenol to give 2,4-dinitrophenol in aqueous solution has been studied under a variety of conditions. At low concentrations of nitrous acid the rate of reaction is dependent upon the concentration of nitrous acid but the rate becomes independent of nitrous acid at high concentrations of nitrous acid when the latter is in excess of 4-nitrophenol concentration. This saturation phenomenon is attributed to the conversion of 4-nitrophenol to its corresponding nitrite ester which then undergoes an acid-catalysed rearrangement to give the accepted normal nitroso σ-complex. Other kinetic parameters, such as salt effects, acidity dependence, and kinetic isotope effects are very similar under the conditions of 'high' and 'low' concentrations of nitrous acid.
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Nitrosation
Nitrous oxide
Nitrophenol
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