Total Nitric Acid Research Articles

Contribution of liquid water content enhancing aqueous phase reaction forming ambient particulate nitrosamines

Contribution of liquid water content (LWC) to the levels of the carcinogenic particulate nitro(so) compounds and the chemistry affecting LWC were investigated based on the observation of seven nitrosamines and two nitramines in rural (Seosan) and urban (Seoul) area in South Korea during October 2019 and a model simulation. The concentrations of both the total nitrosamines and nitramines were higher in Seosan (12.48 ± 16.12 ng/m3 and 0.65 ± 0.71 ng/m3, respectively) than Seoul (7.41 ± 13.59 ng/m3 and 0.24 ± 0.15 ng/m3, respectively). The estimated LWC using a thermodynamic model in Seosan (12.92 ± 9.77 μg/m3) was higher than that in Seoul (6.20 ± 5.35 μg/m3) mainly due to higher relative humidity (75 ± 9% (Seosan); 62 ± 10% (Seoul)) and higher concentrations of free ammonia (0.13 ± 0.09 μmol/m3 (Seosan); 0.08 ± 0.01 μmol/m3 (Seoul)) and total nitric acid (0.09 ± 0.07 μmol/m3 (Seosan); 0.04 ± 0.02 μmol/m3 (Seoul)) in Seosan while neither fog nor rain occurred during the sampling period. The relatively high concentrations of the particulate nitrosamines (>30 ng/m3) only observed probably due to the higher LWC (>10 μg/m3) in Seosan. It implies that aqueous phase reactions involving NO2 and/or uptake from the gas phase enhanced by LWC could be promoted in Seosan. Strong correlation between the concentrations of nitrosodi-methylamine (NDMA), an example of nitrosamines, simulated by a kinetic box model including the aqueous phase reactions and the measured concentration of NDMA in Seosan (R = 0.77; 0.37 (Seoul)) indicates that the aqueous phase reactions dominantly enhanced the NDMA concentrations in Seosan. On the other hand, it is estimated that the formation of nitrosamines by aqueous phase reaction was not significant due to the relatively lower LWC in Seoul compared to that in Seosan. Furthermore, it is presumed that nitramines are mostly emitted from the primary emission sources. This study implies that the concentration of the particulate nitrosamines can be promoted by aqueous phase reaction enhanced by LWC.

Comprehensive stoichiometric studies on the reaction of silicon in HF/HNO3 and HF/HNO3/H2SiF6 mixtures.

The stoichiometry of the wet chemical etching of silicon in concentrated binary and ternary mixtures of HF, HNO3 and H2SiF6 was comprehensively investigated. A complete quantification of both dissolved and gaseous reaction products was carried out for a variety of different acid mixtures. It could be shown that the total nitric acid consumption is directly determined by the concentration of undissociated HNO3 in the mixture and can be attributed to the consumption in subsequent reactions with increasing concentration. Furthermore, a critical minimum concentration of undissociated HNO3 of q(HNO3, undiss) ≥ 0.35 mol kg-1 could be determined, which is required to start the reaction at 20 °C with agitation, irrespective of the composition of the mixture (binary/tertiary). The simultaneous determination of the nitrogen oxides in the gas phase supports the theory that NO is the only direct reduction product of HNO3 in the reaction with Si. Furthermore, the amount of formed hydrogen is determined by both the HF and the HNO3 concentration in the mixture. For binary mixtures, the H2 formation can be quantitatively described as a function of the concentration of HNO3, HF and H2O. The most important finding from comparative investigations between binary and ternary mixtures is that the overall reaction is largely determined by the formation of the reactive intermediate HNO2 as a result of complex reaction pathways. Both the formation and the accumulation of this intermediate are determined by the water content of the etching mixture. The consumption of HNO3 and also the formation of the reaction products NOx and H2 can therefore be functionally described on the basis of the H2O content in the etching mixture, regardless of a binary or ternary mixture.

Partitioning of NH3-NH4+ in the Southeastern U.S.

The formation of inorganic fine particulate matter (i.e., iPM2.5) is controlled by the thermodynamic equilibrium partitioning of NH3-NH4+. To develop effective control strategies of PM2.5, we aim to understand the impacts of changes in different precursor gases on iPM2.5 concentrations and partitioning of NH3-NH4+. To understand partitioning of NH3-NH4+ in the southeastern U.S., responses of iPM2.5 to precursor gases in four seasons were investigated using field measurements of iPM2.5, precursor gases, and meteorological conditions. The ISORROPIA II model was used to examine the effects of changes in total ammonia (gas + aerosol), total sulfuric acid (aerosol), and total nitric acid (gas + aerosol) on iPM2.5 concentrations and partitioning of NH3-NH4+. The results indicate that reduction in total H2SO4 is more effective than reduction in total HNO3 and total NH3 to reduce iPM2.5 especially under NH3-rich condition. The reduction in total H2SO4 may change partitioning of NH3-NH4+ towards gas-phase and may also lead to an increase in NO3− under NH3-rich conditions, which does not necessarily lead to full neutralization of acidic gases (pH < 7). Thus, future reduction in iPM2.5 may necessitate the coordinated reduction in both H2SO4 and HNO3 in the southeastern U.S. It is also found that the response of iPM2.5 to the change in total H2SO4 is more sensitive in summer than winter due to the dominance of SO42− salts in iPM2.5 and the high temperature in summer. The NH3 emissions from Animal Feeding Operations (AFOs) at an agricultural rural site (YRK) had great impacts on partitioning of NH3-NH4+. The Multiple Linear Regression (MLR) model revealed a strong positive correlation between cation-NH4+ and anions-SO42− and NO3−. This research provides an insight into iPM2.5 formation mechanism for the advancement of PM2.5 control and regulation in the southeastern U.S.

Aerosol acidity and liquid water content regulate the dry deposition of inorganic reactive nitrogen

Abstract. Ecosystem productivity is strongly modulated by the atmospheric deposition of inorganic reactive nitrogen (the sum of ammonium and nitrate). The individual contributions of ammonium and nitrate vary considerably over space and time, giving rise to complex patterns of nitrogen deposition. In the absence of rain, much of this complexity is driven by the large difference between the dry deposition velocity of nitrogen-containing molecules in the gas or condensed phase. Here we quantify how aerosol liquid water and acidity, through their impact on gas–particle partitioning, modulate the deposition velocity of total NH3 and total HNO3 individually while simultaneously affecting the dry deposition of inorganic reactive nitrogen. Four regimes of deposition velocity emerge: (i) HNO3 – fast, NH3 – slow, (ii) HNO3 – slow, NH3 – fast, (iii) HNO3 – fast, NH3 – fast, and (iv) HNO3 – slow, NH3 – slow. Conditions that favor partitioning of species to the aerosol phase strongly reduce the local deposition of reactive nitrogen species and promote their accumulation in the boundary layer and potential for long-range transport. Application of this framework to select locations around the world reveals fundamentally important insights: the dry deposition of total ammonia displays little sensitivity to pH and liquid water variations, except under conditions of extreme acidity and/or low aerosol liquid water content. The dry deposition of total nitric acid, on the other hand, is quite variable, with maximum deposition velocities (close to gas deposition rates) found in the eastern United States and minimum velocities in northern Europe and China. In the latter case, the low deposition velocity leads to up to 10-fold increases in PM2.5 nitrate aerosol, thus contributing to the high PM2.5 levels observed during haze episodes. In this light, aerosol pH and associated liquid water content can be considered to be control parameters that drive dry deposition flux and can accelerate the accumulation of aerosol contributing to intense haze events throughout the globe.

Responses of Secondary Inorganic PM2.5 to Precursor Gases in an Ammonia Abundant Area In North Carolina

ABSTRACT Secondary inorganic fine particulate matter (iPM2.5) constitutes a significant amount of the atmospheric PM2.5. The formation of secondary iPM2.5 is characterized by thermodynamic equilibrium gas-particle partitioning of gaseous ammonia (NH3) and aerosol ammonium (NH4+). To develop effective strategies for controlling atmospheric PM2.5, it is essential to understand the responses of secondary iPM2.5 to different precursor gases. In southeastern North Carolina, the amount of NH3 is in excess to fully neutralize acidic gases (i.e., NH3-rich conditions). NH3-rich conditions are mainly attributed to the significant NH3 emissions in the region, especially from the large amounts of animal feeding operation (AFO). To gain a better understanding of the impact of NH3 on the formation of secondary iPM2.5 in this area, the responses of iPM2.5 to precursor gases under different ambient conditions were investigated based upon three-year monitoring data of the chemical components in iPM2.5, gaseous pollutants, and meteorological conditions. The gas ratio (GR) was used to assess the degree of neutralization via NH3, and ISORROPIA II model simulation was used to examine the responses of iPM2.5 to changes in the total NH3, the total sulfuric acid (H2SO4), and the total nitric acid (HNO3). It was discovered that under different ambient temperature and humidity conditions, the responses of iPM2.5 to precursor gases vary. In general, iPM2.5 responds nonlinearly to the total NH3 but linearly to the total H2SO4 and the total HNO3. In NH3-rich regions, iPM2.5 is not sensitive to changes in the total NH3, but it is very sensitive to changes in the total H2SO4 and/or the total HNO3. Reducing the total H2SO4, as opposed to the total HNO3 or the total NH3, leads to a significant reduction in iPM2.5 and is thus a more effective strategy for decreasing the concentration of iPM2.5. This research provides insight into controlling and regulating PM2.5 in NH3-rich regions.

Ground-based spectroscopic measurements of the total nitric acid content in the atmosphere

The results of the first ground-based spectroscopic measurements in Russia of the total content (TC) of nitric acid in the atmosphere near St. Petersburg over the period April 2009–October 2011 are presented. These measurements show a substantial seasonal trend of the HNO3 TC with maximal values in the winter period and early in the spring and minimal values in the summer time. The seasonal trends and variations in the daily mean values of HNO3 TC near St. Petersburg in the winter and spring periods agree well with observations at the Kiruna station of the international NDACC network.

Effects of Aerosol Hygroscopicity on Fine Particle Mass Concentration and Light Extinction Coefficient at Seoul and Gosan in Korea

The sensitivity of aerosol light extinction coefficient to the aerosol chemical composition change is estimated by (1) calculating the aerosol water content and chemical concentrations by a gas/particle equilibrium model and (2) calculating the aerosol light extinction coefficient by a Mie theory based optical model. The major chemical species are total (gas and particle phase) sulfuric acid, total nitric acid, and total ammonia which are based on the measurement data at Seoul and Gosan. At Seoul, since there were enough ammonia to neutralize both total sulfuric acid and total nitric acid, the dry ionic concentration is most sensitive to the variation of the total nitric acid level, while the total mass concentration (ionic concentration plus water content) and thus, the aerosol light extinction coefficient are primarily determined by the total sulfuric acid. At Gosan, since the concentration of ambient sulfuric acid was the highest among the inorganic species, sulfate salts determined aerosol hygroscopicity. Thus, both ionic and total mass concentration, and resultant aerosol light extinction coefficient are primarily determined by the sulfuric acid level.

서울과 고산의 PM2.5수분함량 계절 특성

Water content of <TEX>$PM_{2.5}$</TEX> (particles in the atmosphere with a diameter of less than or equal to a nominal <TEX>$2.5{\mu}m$</TEX>) was estimated by using a gas/aerosol equilibrium model, SCAPE2, for the particles collected at Seoul and Gosan, Korea. From measured and analyzed characteristics of the particles, the largest difference between Seoul and Gosan is the proportions of total ammonia (t-<TEX>$NH_3$</TEX>=gas phase <TEX>$NH_3$</TEX>+particle phase <TEX>${NH_4}^+$</TEX>), total nitric acid (t-<TEX>$HNO_3$</TEX>=gas phase <TEX>$HNO_3$</TEX>+particle phase <TEX>${NO_3}^-$</TEX>) and sulfuric acid (<TEX>$H_2SO_4$</TEX>). Even though both sites have sufficient t-<TEX>$NH_3$</TEX> to neutralize acidic species such as <TEX>$H_2SO_4$</TEX>, t-<TEX>$HNO_3$</TEX>, and t-HCl (total chloric acid=gas phase HCl+particle phase <TEX>$Cl^-$</TEX>), equivalent fraction of t-<TEX>$NH_3$</TEX> and t-<TEX>$HNO_3$</TEX> are higher at Seoul and <TEX>$H_2SO_4$</TEX> is higher at Gosan. Based on the modeling result, it is identified that the <TEX>$PM_{2.5}$</TEX> at Seoul is more hygroscopic than Gosan if the meteorological conditions are the same. To reduce water content of <TEX>$PM_{2.5}$</TEX>, and thus, mass concentration, control measures for ammonia and nitrate reduction are needed for Seoul, and inter-governmental cooperation is required for Gosan.

Study of nitric acid leachout characteristics from weak base anion exchanger to maintain a specified pH regime during Gd(NO3)3 removal from moderator system of 540 MWe PHWRs

AbstractNitric acid leachout characteristics from weak base anion exchanger (WBA) have been experimentally evaluated as a function of total nitric acid loading at a given flow velocity. An empirical first order model is used to explain the column outlet behaviour. Based on the experimental evaluation, a column configuration of a strong acid cation exchanger (SAC) topped mixed bed of SAC and WBA followed by a 5% nitric acid loaded WBA as the bottom layer of the column has been used to remove Gd(NO3)3 from water while maintaining the column outlet pH in the range of 5.0–5.5.

Airborne measurements of the nitric acid partitioning in persistent contrails

Abstract. This study reports the first systematic measurements of nitric acid (HNO3) uptake in contrail ice particles at typical aircraft cruise altitudes. During the CIRRUS-III campaign cirrus clouds and almost 40 persistent contrails were probed with in situ instruments over Germany and Northern Europe in November 2006. Besides reactive nitrogen, water vapor, cloud ice water content, ice particle size distributions, and condensation nuclei were measured during 6 flights. Contrails with ages up to 12 h were detected at altitudes 10–11.5 km and temperatures 211–220 K. These contrails had a larger ice phase fraction of total nitric acid (HNO3ice/HNO3tot = 6%) than the ambient cirrus layers (3%). On average, the contrails contained twice as much HNO3ice as the cirrus clouds, 14 pmol/mol and 6 pmol/mol, respectively. Young contrails with ages below 1 h had a mean HNO3ice of 21 pmol/mol. The contrails had higher nitric acid to water molar ratios in ice and slightly higher ice water contents than the cirrus clouds under similar meteorological conditions. The differences in ice phase fractions and molar ratios between developing contrails and cirrus are likely caused by high plume concentrations of HNO3 prior to contrail formation. The location of the measurements in the upper region of frontal cirrus layers might account for slight differences in the ice water content between contrails and adjacent cirrus clouds. The observed dependence of molar ratios as a function of the mean ice particle diameter suggests that ice-bound HNO3 concentrations are controlled by uptake of exhaust HNO3 in the freezing plume aerosols in young contrails and subsequent trapping of ambient HNO3 in growing ice particles in older (age &gt; 1 h) contrails.

Estimation of the seasonal variation of particulate nitrate and sensitivity to the emission changes in the greater Seoul area

Seasonal variation of fine particulate nitrate and sensitivity of fine particle mass concentration to the emission changes of VOCs and NO x were estimated in the greater Seoul area. SBOX, a photochemical box model was used to obtain the total nitric acid (HNO 3 T) concentration, and SCAPE2, a gas/particle equilibrium model was used to determine the partitioning of nitric acid/nitrate and particulate water content. Most HNO 3 T existed as nitrate except in summer (∼60%) since there was enough ammonia to form particulate ammonium nitrate. In summer, high temperature was favorable to gaseous nitric acid. Also, because of average relative humidity (RH) higher than the deliquescence points of most salts, water content in summer was higher than those in other seasons by a factor of two. For all seasons, fine particle mass concentration (the sum of ion concentrations and water content) increased until considerable amount of NO x emissions was reduced. This phenomenon is a typical example of the so-called ‘NO x disbenefits’ that has been discussed in relation to the abatement of ozone pollution.

Simulation of the thermodynamics and removal processes in the sulfate‐ammonia‐nitric acid system during winter: Implications for PM2.5 control strategies

In the eastern United States, inorganic species account for approximately half of the PM2.5 mass, with sulfate salts comprising the largest fraction. Current strategies for reducing PM2.5 mass concentrations target reducing SO2 to reduce sulfate, but in such a case more ammonium nitrate may form when nitric acid is present. Large‐scale chemical transport models suffer from uncertainties associated with emission inventories. To examine how the inorganic PM2.5 concentration responds to changes in emissions, we introduce an observation‐based box model, the thermodynamic model with removal (TMR), to estimate responses of PM2.5 to precursor concentrations. TMR assumes that particles are in equilibrium with the gas phase, but the removal rate of total (PM2.5 + gas) nitric acid from the system depends on the gas/aerosol partitioning of this species. The model is used to investigate sulfate, total ammonia, and total nitric acid control strategies for western Pennsylvania during the winter using measurements obtained in the Pittsburgh Air Quality Study. Predictions from TMR are compared with observations and predictions of a chemical equilibrium model (GFEMN), where the perturbation of sulfate or total ammonia does not affect the total nitric acid availability. Results show that TMR predicts more aerosol nitrate to form than GFEMN in scenarios where the total ammonia to sulfate ratio is increased, but model results are similar under ammonia‐limited conditions. When sulfate is reduced by 50% during the winter, GFEMN predicts that inorganic PM2.5 mass concentrations will be reduced by 23%, while TMR predicts that there will only be an 8% reduction. For a 50% reduction in ammonia availability, inorganic PM2.5 was reduced by 29%, while for a 50% reduction in total nitric acid a 17% reduction in inorganic PM2.5 was predicted. The analysis suggests the importance of the phase state of the aerosol for the effectiveness of the emission control strategies.

Heavy Metal Pollution by Atmospheric Transport in Natural Soils from the Northern Part of Eastern Carpathians

The present paper is a study of the heavy metal contamination ofnatural soils due to atmospheric transport in the northern partof Eastern Carpathians. The study area is located north of BaiaMare, the main Romanian centre for processing complex sulphideores. Ten undisturbed soil profiles of andosols and andic soilswere investigated. The distribution of heavy metals (Pb, Cu, Zn,Mn, Ni, Co, Cr and Cd) was studied along the soil profile and atspecific distances from the pollution sources. In addition tothe total nitric acid soluble fraction of the metals, amounts oflead, copper, zinc and manganese extractable with 0.05 Mhydrochloric acid were determined to evaluate the fraction ofeach metal potentially available to plants. Surface soils in theIgnis Mountains (10 km from Baia Mare) were more polluted withlead (200–800 ppm), with the concentration decreasing withdistance from the processing plants. Lower lead concentrationswere observed in the deeper soil horizons. The fraction of leadextractable in 0.05 M hydrochloric acid was generally higher athigh total concentrations of lead. From its geographical andsoil profile distributions it is also evident that cadmium wasalso supplied in appreciable amounts to the topsoil from thesame polution sources, whereas the trend was weaker for zincand chromium and not evident for copper, manganese, nickel, orcobalt. The fraction extractable with 0.05 M hydrochloric acidgenerally followed the order Pb > Cu > Zn > Mn.