Higher HNO Research Articles

Reusable HNO Sensors Derived from Cu Cyclam: A DFT Study on the Mechanistic Origin of High Reactivity and Favorable Conformation Changes and Potential Improvements.

Nitroxyl (HNO) exhibits unique favorable properties in regulating biological and pharmacological activities. However, currently, there is only one Cu-based HNO sensor that can be recycled for reusable detection, which is a Cu cyclam derivative with a mixed thia/aza ligand. To elucidate the missing mechanistic origin of its high HNO reactivity and subsequent favorable conformation change toward a stable CuI product that is critical to be oxidized back by the physiological O2 level for HNO detection again, a density functional theory (DFT) computational study was performed. It not only reproduced experimental structural and reaction properties but also, more importantly, revealed an unknown role of the coordination atom in high reactivity. Its conformation change mechanism was found to not follow the previously proposed one but involve a novel favorable rotation pathway. Several newly designed complexes incorporating beneficial effects of coordination atoms and substituents to further enhance HNO reactivity while maintaining or even improving favorable conformation changes for reusable HNO detection were computationally validated. These novel results will facilitate the future development of reusable HNO sensors for true spatiotemporal resolution and repeated detection.

A Surface Micromachining: HNA Etchant for Stiction-free Release of Micro/Nanomechanical Structures

We report a simple and efficient silicon wet etchant HNA (Hydrofluoric acid, Nitric acid, Acetic acid) for the stiction free release of silicon nitride/metal micro/nanomechanical structures. The HNA concentration was varied with the aim of developing a slow etch rate, which could be utilized to suspend the micron and sub-micron cantilever and fixed beam structures. The etch rate was found to decrease with decrease in HF and increase in HNO 3 concentrations. Smooth surface and high selectivity are obtained in case of high HNO 3 content. The obtained etchant with a slow etch rate of 440 nm/minute was successfully utilized for the release of silicon nitride cantilevers and fixed beam structures of 500 nm, 2 µm and 5 µm widths with varying lengths. The resonance frequency of suspended cantilevers characterized by Laser Doppler Vibrometer is in close agreement with the COMSOL simulated resonating frequencies proving that the etching process has been precise without changes to cantilever dimensions. In addition, the generated etchant was successfully used in releasing chrome/gold nanobeams as well without any damage to the metal layers.

Oxidative degradation of bis(2,4,4‐trimethylpentyl)dithiophosphinic acid in nitric acid studied by electrospray ionization mass spectrometry

The selective separation of the minor actinides (Am, Cm) from the lanthanides is a topic of ongoing nuclear fuel cycle research, and dithiophosphinic acids are candidate ligands in these processes. Ligand instability has been noted under radiolytic and harsh acid conditions but explicit degradation pathways for ligands such as bis(2,4,4-trimethylpentyl)-dithiophosphinic acid (CyxH), the major compound in the commercial product Cyanex 301, have been elusive. Organic solutions of CyxH were contacted with aqueous solutions of HNO(3), and their degradation was studied by analyzing samples from these experiments by direct infusion electrospray ionization mass spectrometry. Ions were identified using accurate mass measurement and collision-induced dissociation. The positive ion spectra contained cationized CyxH cluster ions, and oxidatively coupled species (designated Cyx(2)) cationized by either H or Na. The Cyx(2)-derived ions increased with acid contact time. The negative ion spectra consisted almost entirely of the CyxH conjugate base. The negative ion spectra of the HNO(3)-contacted samples also contained conjugate bases corresponding to the dioxo and perthio derivatives of CyxH. CyxH is oxidized by acid contact to form the coupled species Cyx(2), and the dioxo species arise from subsequent oxidation of Cyx(2). Oxidative coupling increases with contact time, and with higher HNO(3) concentrations. The direct infusion measurements provided a simple approach for assessing degradation pathways and kinetics.

Modelling of HNO3-mediated laser-induced condensation: A parametric study

Based on both static (extended Köhler) and dynamic modelling, we investigate the influence of temperature, humidity, HNO(3) initial concentration, as well as of the particle concentration, on the efficiency of HNO(3)-mediated laser-induced condensation. This mechanism is most efficient for low temperatures, high HNO(3) concentration, and relative humidities. It is, however, still active up to 30 °C, down to 70% relative humidity, and below the ppm level of HNO(3). Furthermore, lower particle concentration minimizing the depletion of both HNO(3) and water vapor is more favourable to particle growth.

Supported Pt-particles on multi-walled carbon nanotubes with controlled surface chemistry

Multi-walled carbon nanotubes (MWCNTs) were functionalized by HNO 3 hydrothermal oxidation at 200 °C. The degree of surface functionalization was described by an exponential function in terms of HNO 3 concentration. Very small Pt particles, with mean particle size of 1.7 ± 0.3 nm, could be supported on the surface of pristine MWCNTs and also on MWCNTs treated with HNO 3 concentrations up to 0.20 mol L − 1 , while a broader range of particle sizes, and larger Pt particles (3.4 ± 1.3 nm) were obtained on the MWCNTs treated with a higher HNO 3 concentration (0.30 mol L − 1 ). Therefore, the amounts of surface groups and Pt particle sizes can be selected by tuning the HNO 3 concentration used in the hydrothermal treatment.

Characterization of condensed phase nitric acid particles formed in the gas phase

The formation of nitric acid hydrates has been observed in a chamber during the dark reaction of NO 2 with O 3 in the presence of air. The size of condensed phase nitric acid was measured to be 40–100 nm and 20–65 nm at relative humidity (RH) ≤ 5% and RH = 67% under our experimental conditions, respectively. The nitric acid particles were collected on the glass fiber membrane and their chemical compositions were analyzed by infrared spectrum. The main components of nitric acid hydrates in particles are NHO 3·3H 2O and NO 3 −· xH 2O ( x≤ 4) at low RH, whereas at high RH HNO 3·H 2O, HNO 3·2H 2O, HNO 3·3H 2O and NO 3 −· XH 2O ( x≤ 4) all exist in the condensed phase. At high RH HNO 3· xH 2O ( x≤ 3) collected on the glass fiber membrane is greatly increased, while NO 3 −· xH 2O ( x≤ 4) decreased, compared with low RH. To the best of our knowledge, this is the first time to report that condensed phase nitric acid can be generated in the gas phase at room temperature.

Extraction and stripping of actinide elements with changes in supply flow rate and nitric acid concentration using centrifugal contactors in single cycle solvent extraction system

Counter current experiments in a single cycle solvent extraction system were carried out with centrifugal contactors to study flow rate reductions in extraction solvent and stripping solution with a dissolver solution of irradiated mixed oxide (MOX) fuel. Uranium and Pu leaked to the raffinate with a 15% decrease in the extraction solvent flow rate, which brought about an accumulation of U and Pu in the co-decontamination section. The discharge of other actinide elements and fission products (FPs) in the raffinate was constant when the extraction solvent reduced by 15%. On the other hand, a 15% decrease in the stripping solution flow rate did not affect the stripping of U and Pu so greatly. The polymerization of Pu was not observed in the counter current experiments, and the time taken to change 2% of Pu(IV) to Pu polymers in the stripping section was evaluated. Simulation results based on these experiments showed that a high HNO 3 concentration in the feed solution was advantageous for Np extraction, because Np oxidation progressed in the extraction section.

Particulate matter and gaseous pollutants during a tropical storm and air pollution episode in Southern Taiwan

Gaseous pollutants and PM 2.5 aerosol particles were investigated during a tropical storm and an air pollution episode in southern Taiwan. Field sampling and chemical analysis of particulate matter and gaseous pollutants were conducted in Daliao and Tzouying in the Kaohsiung area, using a denuder-filter pack system during the period of 22 October to 3 November 2004. Sulfate, nitrate and ammonium were the major ionic species in the PM 2.5, accounting for 46 and 39% of the PM 2.5 for Daliao and Tzouying, respectively. Higher PM 2.5, Cl −, NO 3 − and NH 4 +, HNO 2 and NH 3 concentrations were found at night in both stations, whereas higher HNO 3 was found during the day. In general, higher PM 2.5, HCl, NH 3, SO 2, Cl −, NO 3 −, SO 4 2− and NH 4 + concentrations were found in Daliao. The synoptic weather during the experiment was first influenced by Typhoon NOCK-TEN, which resulted in the pollutant concentrations decreasing by about two-thirds. After the tropical thunderstorm system passed, the ambient air quality returned to the previous condition in 12 to 24 h. When there was a strong subsidence accompanied by a high-pressure system, a more stable environment with lower wind speed and mixing height resulted in higher PM 2.5, as well as HNO 2, NH 3, SO 4 2−, Cl −, NO 3 −, NH 4 + and K + concentrations during the episode days. The rainfall is mainly a scavenger of air pollutants in this study, and the stable atmospheric system and the high emission loading are the major reasons for high air pollutant concentrations.

Characteristics of atmospheric nitrogen and sulfur containing compounds in an inland suburban-forested site in northern Kyushu, western Japan

To evaluate the effects of the regional pollutant emission and long-range transport from East Asia of nitrogen and sulfur pollutants on air quality at an inland suburban-forested site in northern Kyushu, western Japan, nitrogen and sulfur pollutants were characterized from May 2006 to April 2007 using an annular denuder system. The annual mean concentration of HNO 3 (2.16 μg m − 3 ) at the study site was comparable to concentrations reported in urban areas. The HNO 3 concentration had a diurnal variation, being higher in daytime and lower at night. The diurnal variation of wind direction suggests air pollutants emitted from the regional urban area were transported to the study site during the daytime and caused a higher HNO 3 concentration. The HNO 3 concentration was significantly higher in summer and spring than in winter. The annual mean concentrations of SO 2 and nss-SO 4 2− (6.52 and 7.70 μg m − 3 , respectively) were higher than concentrations determined in other urban areas and forested areas near urban areas in Japan and other countries. The SO 2 concentration was significantly higher in winter and spring than in summer. Backward trajectory analysis indicates the long-range transport from East Asia partly contributed to the higher concentrations of SO 2 in winter and spring. In contrast, there were no statistical differences in the nss-SO 4 2− concentrations among seasons, which could be explained by increased oxidation of SO 2 to SO 4 2− in summer. The value of sulfur conversion ratio ( F s) being higher throughout the year at the study site (52.6%) than values determined in urban sites and there being no diurnal variation of F s indicates the long-range transport of nss-SO 4 2− not only from East Asia but also from other areas including Japan. The equivalent ratio of NH 4 + and nss-SO 4 2− at the study site (0.96 ± 0.22) indicates that acidic sulfate is neutralized by NH 3, existing mainly as (NH 4) 2SO 4 in fine particles. On the other hand, NH 4NO 3 had scarcely formed at the study site, unlike the case for urban areas. Ca 2+ and Na + are suggested to be the counter ions of NO 3 − in coarse particles, which is similar to the situation for the sites where the concentration of NH 3 is insufficient for NH 4NO 3 to form.

Speciation and Structural Study of U(IV) and -(VI) in Perchloric and Nitric Acid Solutions

In order to elucidate the uranium solution chemistry at the high HNO(3) concentrations typically employed for the reprocessing of spent nuclear fuels, speciation and complex structures of U(IV) and U(VI) are studied in aqueous HNO(3) solutions, as well as in HClO(4) solutions, by means of UV-visible-near-infrared and X-ray absorption spectroscopies and density functional theory calculations. In 1.0 M HClO(4), U(IV) exists as a spherical cation of U(4+), which is surrounded by 9-10 water molecules in the primary coordination sphere, while it forms a colloidal hydrous oxide, U(IV)O(2) x nH(2)O, at a lower acidic concentration of 0.1 M HClO(4). U(VI) exists as a transdioxo uranyl cation, UO(2)(2+), and forms a 5-fold pure hydrate complex of [U(VI)O(2)(H(2)O)(5)](2+) in 1.0 M HClO(4). With increasing HNO(3) concentration, the water molecules of the U(IV) and U(VI) hydrate complexes are successively replaced by planar bidentate coordinating nitrate ions (NO(3)(-)), forming dominant species of [U(IV)(H(2)O)(x)(NO(3))(5)](-) in 9.0 M HNO(3) and [U(VI)O(2)(NO(3))(3)](-) in 14.5 M HNO(3), respectively. The present multitechnique approach also suggests the formation of two intermediate U(VI) species, a 5-fold mononitrato complex ([U(VI)O(2)(H(2)O)(3)(eta(2)-NO(3))](+)) and a 6-fold dinitrato complex ([U(VI)O(2)(H(2)O)(2)(eta(2)-NO(3))(2)](0)), involving an increase in the total coordination number on the uranyl(VI) equatorial plane from 5 to 6 with increasing HNO(3) concentration. The presence of unidentate coordinate nitrato complexes or tetranitrato U(VI) complexes is less probable in the present HNO(3) system.

A sustainable environmentally friendly NO x removal process using Ag(II)/Ag(I)-mediated electrochemical oxidation

This paper presents the results of investigations related to the development of a mediated electrochemical oxidation (MEO) process-based wet scrubbing method for NO and NO 2 abatement from a simulated NO-air flue gas mixture. The Ag(II) redox mediator in nitric acid medium generated in an electrochemical cell was circulated continuously through a packed-bed column by a closed loop, and the NO x gas was oxidatively removed by absorption/oxidation. The outlet gas from scrubber-I was subsequently admitted into scrubber-II for further continuous washings by 3 mol L −1 HNO 3. Numerous experimental runs were carried out in order to observe the performance of the wet scrubber-electrochemical cell integrated system as a function of the operating conditions: the initial NO concentration in the feed (100–400 mg L −1), gas flow rate (0.061–0.243 m s −1), liquid flow rate (0.012–0.049 m s −1), concentration of silver ion mediator (0.01–0.1 mol L −1), nitric acid concentration (3–6 mol L −1), and the temperature (15–45 °C). Low initial NO feed, low gas flow rates, high liquid flow rates, high HNO 3 acid concentration, Ag(I) concentration as low as 0.05 mol L −1 and low temperatures were most suitable for high removal performance. Total removal (100%) of NO and 80% removal of NO x were achieved in the oxidation with electrogenerated Ag(II) in a single stage gas scrubbing in scrubber-I. But, interestingly, a second stage gas scrubbing by a simple HNO 3 (3 mol L −1) wash in scrubber-II led to a better removal of NO x with overall efficiency reaching 90% as well. This is an alternative green treatment process for zero emission of waste gases. Some NO x removal studies were also performed using Ce(IV)/Ce(III) redox mediator system, and the effect of nitric acid concentration and temperature examined, for a comparison with Ag(II)/Ag(I).

Solubility of heavy metals added to MSW

This paper aims to investigate the six heavy metal levels (Cd, Cr, Cu, Pb, Ni and Zn) in municipal solid waste (MSW) at different pHs. It intends to provide the baseline information of metals solubility in MSW co-disposed or co-digested with MSW incinerator ashes in landfill or anaerobic bioreactors or heavy metals contaminated in anaerobic digesters. One milliliter (equal to 1 mg) of each metal was added to the 100 ml MSW and the batch reactor test was carried out. The results showed that higher HNO 3 and NaOH were consumed at extreme pH of 1 and 13 compared to those from pH 2 to 11 due to the comparably higher buffer capacity. Pb was found to have the least soluble level, highest metal adsorption (%) and highest partitioning K d (l g −1) between pH 3 and 12. In contrast, Ni showed the highest soluble level, lowest metal adsorption (%) and lowest K d (l g −1) between pH 4 and 12. Except Ni and Cr, other four metals seemed to show the amphibious properties as comparative higher solubility was found in the acidic and basic conditions.

Selective uptake properties of metal ions by hybrid microcapsules enclosed with TBP

The granulation of TBP extractant is effective for the enhancement of uptake efficiency. The granulation was accomplished by microencapsulating techniques using alginate gel polymers (alginate and alginic acid gel polymers; calcium alginate, barium alginate and nitric alginate (CaALG, BaALG and HALG)). The characterization of hybrid microcapsules was examined by SEM/EPMA, and the uptake properties and the selectivity of various nuclides, Fe(III), Sr(II), Co(II), U(VI) and Pu(IV), were examined by batch methods. A relatively high uptake (%) of Fe(III), Sr(II) and Co(II) above 80% was obtained in the presence of 10 −3 M HNO 3, and the uptake equilibrium was attained within 5 h. The uptake rate of U(VI) and Pu(IV) attained equilibrium within 1 h and 3 h, respectively. At higher HNO 3 concentration ranging from 10 −3 M to 5 M, the uptake (%) of Fe(III), Sr(II) and Co(II) was considerably lowered. In contrast, the uptake (%) of U(VI) and Pu(IV) about 60% was obtained even in the presence of 5 M HNO 3. The uptake of U(VI) for MCs (TBP–CaALG) was governed by the extraction with TBP micro droplets and ion-exchange reaction in the CaALG matrices. Energy dispersive spectra (EDS) showed that U(VI) ions were incorporated into both phases of TBP and CaALG in microcapsules.

The effect of HNO 3 gas on the lichen Ramalina menziesii

Nitric acid (HNO 3) and ozone (O 3), secondary products of photochemical reactions of nitrogen oxides (NO x ) and volatile organic compounds, are important pollutants in arid regions with large outputs from petrol combustion. In the Los Angeles (LA) air basin, nitrogen dry deposition rates in forests downwind of the urban areas can reach 35–40 kg ha −1 year −1, roughly equivalent to the amount of N used to fertilize agricultural fields. The marked decline in the lichen population of the LA air basin has previously been attributed to local O 3 concentration gradients, which overlaid the patterns of species extirpation. Recent research in the air basin has shown that nitrate (NO 3 −) deposition gradients run parallel to the O 3 concentration gradient, and that deposition of NO 3 − and HNO 3 can have significant effects on forest health. Our research examines the effects of HNO 3 dry deposition on the lichen Ramalina menziesii Tayl. in an effort to understand the loss of lichen species in southern California, and increase the usefulness of lichens as biomonitors of nitrogen pollutants. We transplanted healthy R. menziesii thalli from a “pristine” location into fumigation chambers and exposed them to HNO 3 under humid and dry conditions, and moderate and high HNO 3 fumigations. R. menziesii thalli treated with HNO 3 in month-long fumigations experienced a significant decline in chlorophyll content and carbon exchange capacity compared to thalli in control chambers. Leachate conductivity, NO 3 − and K + concentrations increased with HNO 3 fumigation levels and time. We conclude that R. menziesii has an unequivocally negative response to HNO 3 gas concentrations common to ambient summer conditions in the LA air basin.

Atmospheric corrosion effects of HNO 3—Influence of concentration and air velocity on laboratory-exposed copper

A recently developed experimental set-up has been used to explore the atmospheric corrosion effects of nitric acid (HNO 3) on copper, in particular the influence of concentration and air velocity. Characterization and quantification of the corrosion products on exposed samples were performed with Fourier transform infrared (FT-IR) microspectrocscopy, ion chromatography, X-ray diffraction (XRD), micro-balance and microscopy. At low air velocity (0.03 cm s −1) HNO 3 deposition and weight gain of copper increased linearly with concentration up to 400 μg m −3 or 156 ppb. The influence of air velocity on corrosion of copper was tested within the range of 0.03–35.4 cm s −1. Although the air velocity in this study was significantly lower than typical outdoor wind values, a high HNO 3 concentration of the air velocity of 35.4 cm s −1 resulted in a relatively high deposition velocity ( V d) of 0.9 cm s −1 on the metal surface and 1.2 cm s −1 on an ideal absorbent, which would imply a limiting deposition velocity on the copper surface ( V d,surf) of 3.6 cm s −1. Results obtained in this study emphasize the importance for future research on the corrosion effects of HNO 3 on materials as very little has so far been done in this field.

Characterization of gaseous nitrogen oxides in the Lower Fraser Valley during Pacific 2001

Abstract From 13 August–1 September 2001, a number of gaseous chemical compounds were measured at three sites in the Lower Fraser Valley, British Columbia: (1) Slocan—in the city of Vancouver; (2) Langley—in a rural, agricultural area about 35 km southeast of Vancouver; and (3) Sumas—about 65 km inland on a forested mountain (300 m asl). Although the Langley and Sumas sites were located away from major emission sources, CO, NO x and NO y mixing ratios indicate that these sites were often impacted by anthropogenic emissions. At Langley and Slocan, NO and CO mixing ratios were highest between 0400–0700 PDT (UT=PDT−8 h) due to the buildup of fresh vehicular emissions under a nocturnal inversion. At the elevated Sumas site, during the growth of the boundary layer, upward mixing of fresh emissions was observed, delayed by 3 h compared to the other two sites. NO x was the largest component of NO y at Langley and Sumas, averaging 75–80%. At Langley, the HNO 3 fraction of NO y during the afternoon ranged from 15% to 28%, compared to 3 at y at all three sites. The sum of all individual nitrogen oxide species, ∑ NO yi accounted for 85% and 93% of NO y on average at Langley and Sumas, respectively. The chemical age was estimated at the three sites using the ratio (HONO+HNO 3 +PAN)/NO y . The daytime (1400–1800 PDT) ratios at Langley (0.19–0.40) were higher than those at either Slocan (0.04–0.12) or Sumas (0.09–0.19), mainly driven by higher HNO 3 contributions to NO y . The higher ratios at Langley suggest that the extent of processing in air masses at the site during the daytime was greater than at Slocan or Sumas. At Sumas, the elevated nighttime ratios (0.05–0.29) were attributed to transport of more aged air masses to the site and the contribution of HNO 3 from N 2 O 5 hydrolysis. O 3 was only weakly correlated with the oxidation products of NO x at Langley ( m = 2.5 ± 9.1 ) and Sumas ( m = 7.3 ± 8.2 ). Meteorological conditions (lower radiation levels, cooler temperatures) were not favourable for photochemical pollutant processing. The dominant NO x fraction of NO y (see Section 3.2.1) clearly shows that most of the oxidized nitrogen remained in the form of NO x with very limited chemical processing and relatively low O 3 levels.

Measurements of PM10 aerosol and gas-phase nitrous acid during fall season in a semi-urban atmosphere

Abstract Simultaneous measurements of PM 10 (particle mass) aerosol and gas-phase nitrous acid (HNO 2 ) were made over a fall season at a semi-urban site, Kwangju, South Korea, to investigate the effects of agricultural waste burning on their concentrations. The PM 10 aerosol and gaseous species samples were collected three times a day for 6- and 12-h durations using a three-stage filter pack during three intensive sampling campaigns, and analyzed for particulate mass, ionic species, and HNO 3 concentrations. Hourly HNO 2 measurements were also made using a dual channel glass-coil sampling technique and ion chromatography analysis. NO 2 (g) was measured using a differential optical absorption spectroscopy (DOAS) to investigate the formation pathway of HNO 2 . PM 10 , K + , and Cl − concentrations during the agricultural wastes burning event were substantially higher than during any other sampling periods, whereas the concentrations of secondary-formed aerosols, i.e., NO 3 − , NH 4 + , and SO 4 2− , were substantially low during the burning event, compared to those in the non-burning periods. Higher HNO 2 concentrations occurred during the night and November sampling periods when PM 10 mass concentrations were generally high, and lower mixing layer and more humid condition were found, rather than during the day, September, and October sampling periods. It was also found that rapid increase in HNO 2 levels from 0.2 to 2.6 ppb in the afternoon on October 20 was due to direct emissions from the agricultural wastes (straw and stubble) burning practice. Increases in the HNO 2 /NO 2 ratio after sunset, and a close relationship between HNO 2 /NO 2 and the PM 10 mass indicate that during the study period NO 2 is the precursor of HNO 2 production at nighttime.

The extraction of mineral acids by the phosphine oxide Cyanex 923

The distribution equilibria of mineral acids: H 2SO 4, H 3PO 4, HCI, HClO 4 and HNO 3 between aqueous solutions and organic solutions of the phosphine oxide Cyanex 923 in toluene or decane are described. Partition studies have shown that the organic diluent only slightly influences the acid extraction. The extraction mechanism can be related to the solvation of the acid and formation of the L · H m +X m−1 (m = 1, 2 or 3) species in the organic phase, where L is the extractant; only in the case of initial high HNO 33 concentrations is the formation of the L · (HNO 3) 2 species apparent in this phase. The effect of temperature on the acid extraction is also evaluated.

Measurement of atmospheric nitric acid by the filter method and comparisons with the tuneable diode laser and other methods

As part of the Nitrogen Species Methods Comparison Study at Claremont, CA, two triple filter packs and two tuneable diode laser systems were used to measure atmospheric HNO 3; the filters also measured total suspended particulate compounds and gaseous NH 3. The filter packs sampled for 1- and 2-h and 4- and 6-h periods and the lasers operated on 5-min averaging periods. Filter samples from the 4- and 6-h periods yielded, on average, about 16% higher HNO 3 than those from the 1- and 2-h periods. Linear least squares regressions of the 1- and 2-h filter HNO 3 concentrations with the average of the two lasers were highly significant, yielding slopes of 1.22 for daytime and 0.76 for night-time periods. Similar regressions of the 4- and 6-h filter HNO 3 with the laser, annular denuder and denuder difference methods yielded slopes in the range 1.14–1.81. For measurement of atmospheric NH 3, the 4- and 6-h filter results were about 16 % lower than those from the Fourier transform infrared method.

Verification of a mathematical model for aerosol nitrate and nitric acid formation and its use for control measure evaluation

A mathematical model for the formation of atmospheric nitric acid and aerosol nitrate has been developed and employed to study the effect of emission controls. Based on a Lagrangian formulation of the atmospheric diffusion equation, the model computes nitric acid concentrations from a description of daytime photochemical reactions and night-time reactions involving NO 3 and N 2O 5. Ammonium nitrate formation is computed at a thermodynamic equilibrium between HNO 3 and NH 3, and heterogeneous reactions between HNO 3 and preexisting aerosol are considered. The accuracy of the air quality model's predictions is verified by comparison to O 3, NO 2, HNO 3, NH 3, aerosol nitrate and PAN measurements made for this purpose in California's South Coast Air Basin during the period of 30–31 August 1982. Examination of emission control alternatives shows that reduction in NO x emissions yields a nearly proportional decrease in total inorganic nitrate levels (HNO 3 + aerosol nitrates). Reduction in NH 3 emissions suppresses aerosol nitrate formation, resulting in higher HNO 3 levels. Control of organic species emissions by the amounts expected in Los Angeles in future years causes a partial shift away from PAN formation toward greater production of HNO 3. Emission control strategies can be formulated that include a combination of controls on NO x organic gases and NH 3 emissions that will achieve a greater reduction in HNO 3, aerosol nitrate and O 3 levels than a strategy predicated on control of only a single precursor species.