Determination of total gaseous lead in the atmosphere by honeycomb denuder/electrothermal atomic absorption spectrometry.

A technique is described for the determination of total gaseous lead in the atmosphere by honeycomb denuder collection, followed by an electrothermal atomic absorption spectrometry (ETAAS) measurement. The collection efficiency of the honeycomb denuder in which a solution containing 2% HNO3/2% glycerine/1% ammonium dihydrogenphosphate was coated for trapping the gaseous lead in the atmosphere was 98.8%. The linear absorbance response was obtained for a concentration range of 0-1.39 microg m(-3) of lead in the atmosphere. A precision of 4.8% RSD (peak-height absorbance, n = 11) for an aqueous solution of 1 ng of lead standard, characteristic masses (CM) of 23 pg and detection limit (3sigma) of 54 pg for an aqueous solution of 0.01 ng lead standard was achieved with 100 microg ammonium dihydrogenphosphate as a chemical modifier. The average recovery of lead in three standard samples prepared by the independent digestion of NIST SRM 1648 (Urban Particulate Matter) using our analytical system was 97.8%. The total content of the gaseous lead in the atmosphere of our laboratories was 0.35-0.38 microg m(-3).     

Determination of total gaseous selenium in atmosphere by honeycomb denuder/differential pulse cathodic stripping voltammetry

A new analytical method has been developed for the determination of total gaseous selenium in the atmosphere by honeycomb denuder collection followed by differential pulse cathodic stripping voltammetry (DPCSV) measurement. Gaseous selenium was collected in a denuder coating solution containing 2% HNO(3) and 2% glycerine. The soluble product, selenious acid, was then extracted by water for DPCSV analysis. The collection efficiency for gaseous selenium was 99.1% at a flow rate of 1 l min(-1) for 3 h. Excellent linearity in DPCSV was maintained up to Se concentration of 40 ng ml(-1). This was equivalent to a working concentration of 220 ng m(-3) of selenium in the atmosphere. A precision of 1.26% RSD (n=5) for 5 ng Se was obtained, and the detection limit (3sigma) and the quantitative determination limit were estimated to be 0.96 and 3.19 ng m(-3). The average recovery of selenium in three standard samples prepared by independent digestion of NIST SRM 1648 (Urban Particulate Matter) using our analytical system was 99.0%. The total content of gaseous selenium in the atmosphere of our laboratories was 3.2-4.4 ng m(-3).     

Heterogeneous photochemistry of trace atmospheric gases with components of mineral dust aerosol

Mineral dust aerosol is known to provide a reactive surface in the troposphere for heterogeneous chemistry to occur. Certain components of mineral dust aerosol, such as semiconductor metal oxides, can act as chromophores that initiate chemical reactions, while adsorbed organic and inorganic species may also be photoactive. However, relatively little is known about the impact of heterogeneous photochemistry of mineral dust aerosol in the atmosphere. In this study, we investigate the heterogeneous photochemistry of trace atmospheric gases including HNO(3) and O(3) with components of mineral dust aerosol using an environmental aerosol chamber that incorporates a solar simulator. For reaction of HNO(3) with aluminum oxide, broadband irradiation initiates photoreactions to form gaseous NO and NO(2). A complex dynamic balance between surface adsorbed nitrate and gaseous nitrogen oxide products including NO and NO(2) is observed. For heterogeneous photoreactions of O(3), iron oxide shows catalytic decompositions toward O(3) while aluminum oxide is deactivated by ozone exposure. Furthermore, the role of relative humidity, and, thus, adsorbed water, on heterogeneous photochemistry has been explored. The atmospheric implications of these results are discussed.     

Uptake of HNO3 on hexane and aviation kerosene soots

The uptake of HNO(3) on aviation kerosene (TC-1) soot was measured as a function of temperature (253-295 K) and the partial pressure of HNO(3), and the uptake of HNO(3) on hexane soot was studied at 295 K and over a limited partial pressure of HNO(3). The HNO(3) uptake was mostly reversible and did not release measurable amounts of gas-phase products such as HONO, NO(3), NO(2) or N(2)O(5). The heat of adsorption of HNO(3) on soot was dependent on the surface coverage. The isosteric heats of adsorption, Delta(0)H(isosteric), were determined as a function of coverage. Delta(0)H(isosteric) values were in the range -16 to -13 kcal mol(-1). The heats of adsorption decrease with increasing coverage. The adsorption data were fit to Freundlich and to Langmuir-Freundlich isotherms. The heterogeneity parameter values were close to 0.5, which suggested that a HNO(3) molecule can occupy two sites on the surface with or without being dissociated and that the soot surface could be nonuniform. Surface FTIR studies on the interaction of soot with HNO(3) did not reveal formation of any minor product such as organic nitrate or nitro compound on the soot surface. Using our measured coverage, we calculate that the partitioning of gas-phase nitric acid to black carbon aerosol is not a significant loss process of HNO(3) in the atmosphere.     

Annular diffusion denuder for simultaneous removal of gaseous organic compounds and air oxidants during sampling of carbonaceous aerosols

A specially designed annular diffusion denuder for simultaneous removal of organic gaseous compounds and atmospheric oxidants in carbonaceous aerosol sampling is presented. Various kinds of denuder coatings were compared with respect to the collection efficiency of both organic gaseous compounds and NO₂ and ozone. The optimum sorbent is a mixture of activated charcoal and sulfite on molecular sieve. To ensure high collection efficiency over long-term field operation, two annular diffusion denuders are combined in series. The first half of the first denuder is filled with Na₂SO₃ on molecular sieve (23 cm long layer) while the second half of the first denuder and the whole second denuder are filled with activated charcoal (the total length of the charcoal section is 67 cm).     

New experimental and theoretical approach to the heterogeneous hydrolysis of NO2: key role of molecular nitric acid and its complexes

Although heterogeneous chemistry on surfaces in the troposphere is known to be important, there are currently only a few techniques available for studying the nature of surface-adsorbed species as well as their chemistry and photochemistry under atmospheric conditions of 1 atm pressure and in the presence of water vapor. We report here a new laboratory approach using a combination of long path Fourier transform infrared spectroscopy (FTIR) and attenuated total reflectance (ATR) FTIR that allows the simultaneous observation and measurement of gases and surface species. Theory is used to identify the surface-adsorbed intermediates and products, and to estimate their relative concentrations. At intermediate relative humidities typical of the tropospheric boundary layer, the nitric acid formed during NO2 heterogeneous hydrolysis is shown to exist both as nitrate ions from the dissociation of nitric acid formed on the surface and as molecular nitric acid. In both cases, the ions and HNO3 are complexed to water molecules. Upon pumping, water is selectively removed, shifting the NO(3-)-HNO3(H2O)y equilibria toward more dehydrated forms of HNO3 and ultimately to nitric acid dimers. Irradiation of the nitric acid-water film using 300-400 nm radiation generates gaseous NO, while irradiation at 254 nm generates both NO and HONO, resulting in conversion of surface-adsorbed nitrogen oxides into photochemically active NO(x). These studies suggest that the assumption that deposition or formation of nitric acid provides a permanent removal mechanism from the atmosphere may not be correct. Furthermore, a potential role of surface-adsorbed nitric acid and other species formed during the heterogeneous hydrolysis of NO2 in the oxidation of organics on surfaces, and in the generation of gas-phase HONO on local to global scales, should be considered.     

A denuder-impinger system with in situ derivatization followed by gas chromatography-mass spectrometry for the determination of gaseous iodine-containing halogen species

Reactive iodine species have been suggested to play an important role in the atmosphere (e.g. tropospheric ozone depletion, coastal new particle formation). However, there still exist major uncertainties about their atmospheric chemistry, mostly due to the lack of analytical approaches for the accurate speciation of certain key compounds. In this study, 1,3,5-trimethoxybenzene (1,3,5-TMB)-coated denuder proved to be suitable for the differentiation between gaseous interhalogens (iodine monochloride (ICl), iodine monobromide (IBr)) and molecular iodine (I2) based on a selective collection/derivatization method. The results of the denuder sampling were compared with the results of impinger sampling in water, methanol and carbon tetrachloride solutions of 1,3,5-TMB. ICl and IBr are converted into 1-iodo-2,4,6-trimethoxybenzene (1-iodo-2,4,6-TMB) and 1-bromo-2,4,6-trimethoxybenzene (1-bromo-2,4,6-TMB), respectively, in the denuder systems. The respective collection efficiency is 99.2% for ICl and 92.6% for IBr, at 500mLmin(-1) gas flow rate. The collection efficiency for I2 is lower than 1% in the same denuder system, but significantly increases to about 90% in the aqueous 1,3,5-TMB loaded impinger. The denuder-impinger coupled system was then used to differentiate and to collect the ICl, IBr and I2 gas mixtures, followed by gas chromatography-ion trap mass spectrometry (GC-MS) determination. The precision of the method is in general better than 9.1%. The parameters affecting denuder operation including sampling flow rate, sampling duration, and relative humidity have been evaluated. The presented method provides an attractive protocol for iodine species analysis for atmospheric chemistry research.     

A new method for the measurement of trace amounts of HONO in the atmosphere using an air-dragged aqua-membrane-type denuder and fluorescence detection

A new method for the measurement of trace amounts of HONO has been developed. Nitrous acid in the ambient air is absorbed in an aqueous solution by an air-dragged aqua-membrane-type denuder. The absorbed nitrite is reacted with 2,3-diaminonaphthalene, and the formed 1-naphthotriazol is measured using a fluorescence method. The calibration curve of HONO shows a straight line from 0 to 4000 ppt, and the detection limit is estimated to be 8.1 ppt calculated as being three times of the base line noise. The time resolution, which is defined as the time required to become a constant value by changing from 0 to ca. 1000 ppt was 2 min. The present method is not affected by NO(2), NO, SO(2), O(3) NH(3) or mixtures of these gases and organic nitrate, organic carboxylic acids, alcohols and aldehydes. The determination results of HONO concentrations in the ambient air by the present method are in good agreement with those by the annular denuder system and the differential optical absorption method.     

Reaction Channels of HCO with NO Study by Time-resolved TR-FTIR Spectroscope

The gaseous reaction of CH+NO2 has been investigated experimentally. CH radical was generated by multiple photon photolysis of CHBr3 at 248 nm. Vibrationally excited species of HCO (ν3), CO(v), CO2(ν3), HNO (ν1), OH(v) were detected as emitters of CH+NO2 reaction by time-resolved Fourier transform spectroscope. Three exothermic reaction channels leading to HCO+NO, NH+CO2, CO+HNO, are identified. The minor reaction leading to OH+NCO may also occur.     

Parahalogenated phenols accelerate the photochemical release of nitrogen oxides from frozen solutions containing nitrate

The photolysis of nitrate anion (NO(3)(-)) contained in surface ice and snow can be a regionally significant source of gas-phase nitrogen oxides and affect the composition of the planetary boundary layer. In this study, the photochemical release of nitrogen oxides from frozen solutions containing NO(3)(-) in the presence of organic compounds was investigated. Gas-phase nitrogen oxides were quantified primarily by NO-O(3) chemiluminescence detection of NO and NO(y) (=NO + NO(2) + HONO + HNO(3) + ∑PAN + ∑AN ...) and cavity ring-down spectroscopy of NO(2) and total alkyl nitrates (∑AN). The photochemical production of gas-phase NO(y) was suppressed by the presence of formate, methanesulfonate, toluene, or phenol. In contrast, para-halogenated phenols (in the order of Cl > Br > F) promoted the conversion of NO(3)(-) to gas-phase NO(y), rationalized by acidification of the ice surface.     

New insights in the atmospheric HONO formation: new pathways for N2O4 isomerization and NO2 dimerization in the presence of water

Isomerization of N(2)O(4) and dimerization of NO(2) in thin water films on surfaces are believed to be key steps in the hydrolysis of NO(2), which generates HONO, a significant precursor to the OH free radical in lower atmosphere and high-energy materials. Born-Oppenheimer molecular dynamics simulations using the density functional theory are carried out for NO(2)(H(2)O)(m), m ≤ 4, and N(2)O(4)(H(2)O)(n) clusters, n ≤ 7, used to mimic the surface reaction, to investigate the mechanism around room temperature. The results are (i) the NO(2) dimerization and N(2)O(4) isomerization reactions occur via two possible pathways, the non-water-assisted and water-assisted mechanisms; (ii) the NO(2) dimerization in the presence of water yields either ONONO(2)(H(2)O)(m) or NO(3)(-)NO(+)(H(2)O)(m) clusters, but it is also possible to form the HNO(3)(NO(2)(-))(H(3)O(+))(H(2)O)(m-2) transition state to form HONO and HNO(3), directly; (iii) the N(2)O(4) isomerization yields the NO(3)(-)NO(+)(H(2)O)(n) cluster, but it does not hydrolyze faster than the NO(2)(+)NO(2)(-)(H(2)O)(n) hydrolysis to directly form the HONO and HNO(3). New insights for hydrolysis of oxides of nitrogen in and on thin water films on surfaces in the atmosphere are discussed.     

Enhanced surface photochemistry in chloride-nitrate ion mixtures

Heterogeneous reactions of sea salt aerosol with various oxides of nitrogen lead to replacement of chloride ion by nitrate ion. Studies of the photochemistry of a model system were carried out using deliquesced mixtures of NaCl and NaNO3 on a Teflon substrate. Varying molar ratios of NaCl to NaNO3 (1 : 9 Cl- : NO3-, 1 : 1 Cl- : NO3-, 3 : 1 Cl- : NO3-, 9 : 1 Cl- : NO3-) and NaNO3 at the same total concentration were irradiated in air at 299 +/- 3 K and at a relative humidity of 75 +/- 8% using broadband UVB light (270-380 nm). Gaseous NO2 production was measured as a function of time using a chemiluminescence NO(y) detector. Surprisingly, an enhanced yield of NO2 was observed as the chloride to nitrate ratio increased. Molecular dynamics (MD) simulations show that as the Cl- : NO3- ratio increases, the nitrate ions are drawn closer to the interface due to the existence of a double layer of interfacial Cl- and subsurface Na+. This leads to a decreased solvent cage effect when the nitrate ion photodissociates to NO2+O*-, increasing the effective quantum yield and hence the production of gaseous NO2. The implications of enhanced NO2 and likely OH production as sea salt aerosols become processed in the atmosphere are discussed.     

Determination of nitric acid in ambient air using diffusion denuder tubes

A method has been developed for the determination of gaseous nitric acid in air based on its separation from particulate nitrate aerosol using diffusion denuder tubes. An integrated value of nitric acid concentration in air is obtained. The experimentally derived absorption efficiencies of the diffusion denuder tubes ranged from 87.6 to 96.9%. The standard deviation of the method was calculated as 0.10 mug/m(3) for nitric acid concentrations in the range 0.54-1.72 mug/m(3). A correction procedure, using two diffusion denuders in series, should be applied if measurements are made in the presence of high levels of nitrogen oxides.     

Comparison of denuder and impinger sampling for determination of gaseous toluene diisocyanate (TDI)

An air-sampling method employing denuders coated inside with a chemisorptive stationary phase has been evaluated for analysis of the hazardous gaseous 2,4 and 2,6 isomers of toluene diisocyanate (TDI). The denuder stationary phase consisted of polydimethylsiloxane (SE-30) to which dibutylamine (DBA) was added as a reagent for derivatization of TDI. The accuracy and precision of sampling by means of denuders were shown to differ only slightly from those of the established impinger method. The denuder method was, however, also shown to be suitable for long-term measurements (up to 8 h). The limit of determination (LOD) of the method, including LC-APCI-MS-MS analysis, was found to be 1.9 microg m(-3) and 1.2 microg m(-3) for 2,4- and 2,6-TDI, respectively, for short-term measurements (15 min). Significant lower LOD was obtained for long-term measurements. This is well below the Occupational Safety and Health Administration (OSHA) 8-h TWA (time-weighted average) exposure limit, which is 40 microg m(-3) for the sum of the TDI isomers. The denuder method was also found to be robust and easy to handle. The samplers can be prepared several days before sampling with no loss in performance. The contents of denuders should, on the other hand, be extracted immediately after sampling to prevent degradation of the isocyanate derivatives formed.     

Studies on the Use of Commercial Capillary Gas Chromatographic Columns as Diffusion Denuders

The possibility of using a piece of gas chromatographic capillary column as a tubular denuder for isolation and enrichment of organic pollutants present in air was studied. The partition coefficients (K_fs) of typical organic pollutants (benzene, chlorobenzene, toluene) between the gaseous phase and the denuder sorption layer were determined and effects of analyte concentration in the gaseous phase and gas flow rate on partitioning were studied. The partition coefficients were found to be constant in the studied range of concentration and gaseous mixture flow rate. A piece of a capillary column coated with polydimethylosiloxane can be used as a tubular denuder.     

HNO3-UO2(NO3)2-H2O系统的活度系数的测定和计算

用H^+和NO3^-离子选择电极组成的电池用电势法测定了HNO3-UO2(NO3)2-H2O系统在25°C时的HNO3的平均活度系数, 求得了同时含有^E0和 ^S0-I关系式的Pitzer方程中的两粒子和三粒子作用参数(^s0(0), ^s(1),Ψ)。用Pitzer方程计算了该系统中水的活度, 并用Pitzer方程、Mckay-Perring方法和Harned方程分别计算了系统中HNO3和UO2(NO3)2的平均活度系数。     

Determination of N-nitrosomethylaniline and methylaniline in the gas phase

A method is described for selective sampling and determination of gaseous N-nitrosomethylaniline (NMA) and methylaniline (MA) in air without artifacts. Therefore a denuder system is developed to distinguish between the amine and the nitroso compound during sampling. A spatial separation of the gas phase of these compounds is realized. The detection is performed after gas Chromatographic separation with a thermal energy analyzer (TEA) for the nitrosamine and with flame ionization detector (FID) for the amine and nitrosamine. Besides the sampling technique, the extraction of the samples and detection principles are described. To prove that the formation of artifacts does not appear, the influence of humidity and nitrogen oxides was investigated.Dedicated to Professor Dr. H. Malissa on the occasion of his 75th birthday     

Nonlinear vibrational spectroscopic studies of the adsorption and speciation of nitric acid at the vapor/acid solution interface

Nitric acid plays an important role in the heterogeneous chemistry of the atmosphere. Reactions involving HNO(3) at aqueous interfaces in the stratosphere and troposphere depend on the state of nitric acid at these surfaces. The vapor/liquid interface of HNO(3)-H2O binary solutions and HNO(3)-H(2)SO(4)-H2O ternary solutions are examined here using vibrational sum frequency spectroscopy (VSFS). Spectra of the NO2 group at different HNO(3) mole fractions and under different polarization combinations are used to develop a detailed picture of these atmospherically important systems. Consistent with surface tension and spectroscopic measurements from other laboratories, molecular nitric acid is identified at the surface of concentrated solutions. However, the data here reveal the adsorption of two different hydrogen-bonded species of undissociated HNO(3) in the interfacial region that differ in their degree of solvation of the nitro group. The adsorption of these undissociated nitric acid species is shown to be sensitive to the H2O:HNO(3) ratio as well as to the concentration of sulfuric acid.     

Use of HNO(3) as the source of NO to prepare a nitric oxide complex of ruthenium

Reaction of cis-Ru(bisox)(2)Cl(2), where bisox is 4,4,4',4'-tetramethyl-2,2'-bisoxazoline, with HNO(3) in 1 : 4 molar proportion in boiling water under N(2) atmosphere and subsequent addition of an excess of NaClO(4).H(2)O yields [Ru(bisox)(HL)(NO)](ClO(4))(NO(3)) (1). HL is a hydrolysed form of bisox where one of the oxazoline rings opens up. X-Ray crystallography shows that 1 contains an octahedral RuN(5)O core. HL binds the metal through an imino N, an amide N and an alcoholic O atom. Reaction of cis-Ru(bisox)(2)Cl(2) with an excess of NaNO(2) in water gives cis-Ru(bisox)(2)(NO(2))(2) (2). On acidification by HClO(4) in methanol, is smoothly converted to cis-[Ru(bisox)(2)(NO(2))(NO)](ClO(4))(2) (3) due to equilibrium (1). [formula: see text] (1) The X-ray crystal structures of 2 and 3 have also been determined. NO binds Ru in 1 and 3 linearly. The Ru-NO bond length in 1 is 1.764(13) A and that in 3 is approximately 1.78 A. All the three complexes have been characterised by FTIR, NMR and ESIMS. The NO stretching frequencies in 1 and 3 are 1897 and 1936 cm(-1) respectively. While 3 reverts back to 2 readily in presence of OH(-) [equilibrium (1)], 1 does not react with OH(-). It is concluded that while in the reaction of cis-Ru(bisox)(2)Cl(2) with HNO(3), bisox is hydrolysed following abstraction of NO from HNO(3), generation of the nitrosyl complex 3 via reaction (1) is not accompanied with such hydrolysis.     

The determination of hydrogen chloride in ambient air with diffusion/denuder tubes

A manual method for the determination of hydrogen chloride in air, based on diffusion/denuder tube separation from particulate chloride aerosol is described. When air is drawn through a tube coated with a selective absorbent (sodium fluoride), separation is achieved because gaseous hydrogen chloride diffuses much more rapidly to the tube walls than particulate chloride aerosol, which passes through virtually unabsorbed. After the sampling period (the length of which depends on the concentration of gaseous hydrogen chloride expected), the sorbed hydrogen chloride is washed from the tube and measured with a highly sensitive chloride ion-selective electrode with a mercury (I) chloride membrane. The method is examined theoretically and experimentally. The experimentally derived absorption efficiencies of the diffusion/denuder tubes were > 90% and the standard deviation of the method was 0.023 μg m^?3 for hydrogen chloride concentrations of 0.16–0.55 μg m^?3. Interference from particulate chloride salts was negligible; this was confirmed by tests with artificially generated aerosol particles from an aerosol generator. The diffusion/denuder tubes have high capacity; level as high as 330 μg m^?3 hydrogen chloride can be sampled for 60 min without affecting performance. A detection limit of (50/t) μg m^?3 can be achieved, where t is the sampling rime (min); e.g., 1μg m^?3 hydrogen chloride can be detected with a sampling period of 50 min.