The Effect of Heterogeneous Reactions on Model Performance for Nitrous Acid
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Nitrous acid
Nitric acid
Nitrous oxide
Acid rain
Hydroxyl radical
Atmospheric chemistry
The nitrous oxide is determined by the content of (NOx) in the strong nitric acid, the increase of nitrous oxide by the way of either acid decomposition or temperature modification[1], [2] influence the safe production of military products and environmental pollutions[3]. The required specifications of the acids should meet the requirement of desired industry and safety during the transportations from site to site and storage. If the specifications (nitrous oxide) changed rapidly during transportation, decomposition takes place. It is believed that the Sudanese ambient temperature plays the main role. The strong nitric acid that has been stored for long time and transferred away will thermally and catalytically decompose and specifications will change. This study aims to develop a set of preliminary guide lines and recommendations for stabilizing the nitrous oxide (HNO2) in strong nitric acid. The equilibrium relations between acids systems (Nitrous oxide NOx expressed by "nitrous acid HNO2 concentration" and strong nitric acid HNO3) were reviewed and explained. The effects of Sudan ambient temperatures on acceleration of nitrous oxide (HNO2) in strong nitric acid, determine the optimum cooling temperature to slow the decomposition and to stabilize the nitrous oxide were investigated. This is done through incubation of three samples of strong nitric acid (97.5%) at the temperatures 20°C, 25°C and 30°C. Laboratory analysis was done to observe the nitrous oxide exit rate as function of temperatures, concentration of strong nitric acid within four days, Table I, II, III and Fig. 2, 4, 6 show the obtained experimental data. A noticeable increase of nitrous oxide at respective temperatures (20 0C, 25 0C, 30 0C) at the beginning was observed then the curve levels after three days’ incubation. It is concluded that (200C) is the higher temperature at which the strong nitric acid is either stored or transported. Hence it is the optimum temperature to slow the decomposition and stabilize the nitrous oxide. Recommendations for checking Strong Nitric Acid storage tank, transportation system design and design of a conventional jacket heat exchanger to cool nitric acid from (40 0C to 20 0C) were made.
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The hydroxyl (OH) radical is the most important oxidant in the atmosphere since it controls its self-oxidizing capacity. The main sources of OH radicals are the photolysis of ozone and the photolysis of nitrous acid (HONO). Due to the attenuation of solar radiation in the indoor environment, the possibility of OH formation through photolytic pathways indoors has been ignored up to now. In the indoor air, the ozonolysis of alkenes has been suggested as an alternative route of OH formation. Models and indirect measurements performed up to now according to this hypothesis suggest concentrations of OH radicals on the order of 10 4 –10 5 molecules per cubic centimeter. Here, we present direct measurements of significant amounts of OH radicals of up to 1.8⋅10 6 molecules per cubic centimeter during an experimental campaign carried out in a school classroom in Marseille. This concentration is on the same order of magnitude of outdoor OH levels in the urban scenario. We also show that photolysis of HONO is an important source of OH radicals indoors under certain conditions (i.e., direct solar irradiation inside the room). Additionally, the OH concentrations were found to follow a linear dependence with the product J(HONO)⋅[HONO]. This was also supported by using a simple quasiphotostationary state model on the OH radical budget. These findings force a change in our understanding of indoor air quality because the reactivity linked to OH would involve formation of secondary species through chemical reactions that are potentially more hazardous than the primary pollutants in the indoor air.
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Hydroxyl radical
Oxidizing agent
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Nitrogen dioxide
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The nitrous oxide is determined by the content of (NOx) in the strong nitric acid, the increase of nitrous oxide by the way of either acid decomposition or temperature modification[1], [2] influence the safe production of military products and environmental pollutions[3]. The required specifications of the acids should meet the requirement of desired industry and safety during the transportations from site to site and storage. If the specifications (nitrous oxide) changed rapidly during transportation, decomposition takes place. It is believed that the Sudanese ambient temperature plays the main role. The strong nitric acid that has been stored for long time and transferred away will thermally and catalytically decompose and specifications will change. This study aims to develop a set of preliminary guide lines and recommendations for stabilizing the nitrous oxide (HNO2) in strong nitric acid. The equilibrium relations between acids systems (Nitrous oxide NOx expressed by "nitrous acid HNO2 concentration" and strong nitric acid HNO3) were reviewed and explained. The effects of Sudan ambient temperatures on acceleration of nitrous oxide (HNO2) in strong nitric acid, determine the optimum cooling temperature to slow the decomposition and to stabilize the nitrous oxide were investigated. This is done through incubation of three samples of strong nitric acid (97.5%) at the temperatures 20°C, 25°C and 30°C. Laboratory analysis was done to observe the nitrous oxide exit rate as function of temperatures, concentration of strong nitric acid within four days, Table I, II, III and Fig. 2, 4, 6 show the obtained experimental data. A noticeable increase of nitrous oxide at respective temperatures (20 0C, 25 0C, 30 0C) at the beginning was observed then the curve levels after three days’ incubation. It is concluded that (200C) is the higher temperature at which the strong nitric acid is either stored or transported. Hence it is the optimum temperature to slow the decomposition and stabilize the nitrous oxide. Recommendations for checking Strong Nitric Acid storage tank, transportation system design and design of a conventional jacket heat exchanger to cool nitric acid from (40 0C to 20 0C) were made.
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Nitrous oxide
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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.
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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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Acid rain
Atmospheric chemistry
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The hydroxyl radical plays a critical role in the chemistry of the lower atmosphere. Understanding its production, interconversion, and sinks is central to modeling and predicting the chemistry of the troposphere. The OH measurements made during the 1993 Tropospheric OH Photochemistry Experiment provide a detailed look at these mechanisms since NO x , j (O 3 ), RO 2 , HO 2 , nonmethane hydrocarbons (NMHC), and many other relevant species were measured simultaneously. The relationship of OH to NO x and to primary production is extensively examined. Close agreement with theory is shown in the NO x /OH relation with OH concentrations increasing with increasing NO to a maximum at 1–2 ppbv due to conversion of HO 2 to OH, and then OH decreasing with further increasing NO x due to conversion of NO 2 to HNO 3 . Close correlations of OH concentrations with primary production (water, ozone, j (O 3 )) are also shown both on average and on rapid timescales.
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