Measurements of ammonia flux to a spruce stand in Denmark

This work demonstrates the existence of a linear relation between the deposition velocity of ammonia and the friction velocity measured above a spruce stand in the western part of Denmark. In order to estimate the ammonia deposition velocity and flux to a Norway spruce forest, concentration gradients of ammonia and several meteorological parameters were measured in a meteorology tower during two periods, 1 week in spring and 1 week in late summer 1991. The estimated deposition velocities lie in the range −0.125 to 0.201 m s⁻¹, with a mean of 0.026 m s⁻¹. The deposition velocity and the flux were generally largest in the afternoon. On the basis of 24-h measurements of ammonia and routine meteorological measurements the relation between deposition velocity and friction velocity is extrapolated to an estimate of the average flux for the growing season May to September 1991. The estimate gave an average flux of 87 μg NH₃N m⁻² h⁻¹ (=0.02 μg NH₃N m⁻² s⁻¹). The average deposition velocity for the period was 0.045 m s⁻¹.     

Monitoring the dry deposition of SO2 in the Netherlands: Results for grassland and heather vegetation

An automated system based on the micrometeorological gradient technique has been developed to measure the dry deposition of SO₂ on a routine basis. Measurements were made at two locations in the Netherlands. From these results dry deposition fluxes, dry deposition velocities and surface resistances for a heathland and for an agricultural grassland site were estimated using a selected set of data and a calculation procedure based on micrometeorological considerations. An extensive analysis was made to determine uncertainties in the resulting deposition parameters. From this analysis it has been concluded that the uncertainty in these parameters is almost completely determined by the random errors in measured concentrations. The meteorological surface exchange parameters can be estimated sufficiently accurately (<20% uncertainty). At the grassland site, average surface resistances to deposition of 6(±8) and 13(±12) s m⁻¹ were calculated for wet and dry conditions, respectively. At the heathland site, a similar distinct difference between R_c values for wet and dry conditions was found. These values are 20(±21) and 70(±90) s m⁻¹, respectively. The yearly average dry deposition flux for SO₂ at the grassland site amounts to 585(±330) mol ha⁻¹ yr⁻¹, while at the heathland site the yearly average flux was 300(±270) mol ha⁻¹ yr⁻¹. The yearly average dry deposition velocity at 4 m height was 1.2(±0.3) cm s⁻¹ at the grassland site and 0.8(±0.4) cm s⁻¹ at the heathland site.     

How well are hydraulic conductivity variations approximated by additive stable processes?

Analysis of the higher statistical moments of a hydraulic conductivity (K) and an intrinsic permeability (k) data set leads to the conclusion that the increments of the data and the logs of the data are not governed by Levy-stable or Gaussian distributions. The distribution tails appear to display a Pareto-like power-law decay (i.e. Prob(|x|>s|)∝s^−α as s→∞), with α values of ≈2.5 and 3.6, respectively. Unlike the calculations of Liu and Molz (1997), α values were largely independent of lag size. These results suggest that the Levy model does not fit the tail behavior of the data well, even prior to the need for truncation in order to keep the statistical moments of simulated K distributions from becoming unrealistically large. It is suggested also that the fractional diffusion equation, based on an underlying Levy motion rather than the usual Brownian motion, might be better justified if porosity variations, as well as K variations, were considered. For the past 10 years, hydrologists and petroleum scientists have explored the use of non-stationary stochastic processes with stationary increments as models for log hydraulic conductivity distributions — the so-called scaling fractal models. Initially, Gaussian processes were used based on fractional Brownian motion. Later, a non-Gaussian model, fractional Levy motion, was suggested as a more realistic alternative. Even more recently, Levy multi-fractals have been proposed as direct models for K variations. In the on-going effort to arrive at the most practical and realistic model for K or log(K) increments, the present communication attempts to develop useful information by presenting a careful analysis of the tail behavior of K and log(K) data sets. It is concluded that although more realistic than the Gaussian model, the Levy model over-estimates the variability inherent in the two carefully measured data sets that were studied.     

Interdependence of the slopes and intercepts from log-log correlations of measured gas-particle paritioning and vapor pressure—I. theory and analysis of available data

Gas-particle partitioning is examined using a partitioning constant K_p = (F/TSP)/A, where F (ng m⁻³) and A (ng m⁻³) are the particulate-assiociated and and concentrations, respectively, and TSP is the total suspended particulate matter level (μg m⁻³). At a given temperature and for a given sample of particulate matter, compound-dependent values of K_p tend to be correlated with the sub-cooled liquid vapor pressure (p_L⁰, toor according to log K_p = m_r log p_L⁰+b_m. Theory predicts that b_r values should be somewhat similar, and that m_r values should be near −1. This is supported by field and laboratory work. However, there is still noticeable variability in reported m_r and b_r values, even when obtained by the same researchers sampling in the same location. Three possible thermodynamic sources of variability include variability in the compound-to-compound differences in the thermodynamics of adsorption, event-to-event variability in the specific surface area of the aerosol and event-to-event variability in the ambient temperature. Non-thermodynamic sources of variability include sorption of gaseous analytes to the filters used in differentiating between F and A, the presence of non-exchangeable component in the measured F values, within-event adsorption/desorption kinetics, within-event changes in contaminant levels, and within-event changes in temperature. Each of these sources of variability operate in their own way to cause variability in m_r and b_r. In general, one can expect there to be a correlation in the obseved m_r and b_r of the form b_r = m_sm_r+b_s. For the study of Yamasaki et al. (1982, Envir. Sci. Technol. 16, 189–194), one obtains m_s = 5.77 and b_s = −2.18, with r² = 0.91. In the presence of such a correlation, one can expect that all log (F/TSP)/A vs log p_L⁰ plot will tend to intersect at the same (x,y) poitn given by (−m_s, b_s. Exisiting field and laboratory data show this tendency.     

Fluxes of nitric and nitrous oxides from agricultural soils in a cool temperate climate

Fluxes of NO and N₂O from sandy loam soils cropped with winter wheat and a clay loam soil under ryegrass, with and without the addition of NH₄NO₃ fertilizer, were measured using static and dynamic chamber methods. Nitric oxide fluxes ranged from −0.3 (deposition) to 6.9 (emission) ng NO-N m⁻² s⁻¹. The corresponding N₂O flux ranged from 0 to 91 (emission) ng N₂O-N m⁻² s⁻¹. The NO flux was temperature dependent. Activation energies ranged from 40 to 81 kJ mol⁻¹. Nitric oxide and N₂O fluxes increased linearly with soil available nitrogen (NH₄ + NO₃). Emissions of NO and N₂O were not detectable from unfertilized ryegrass plots. Instead, nitric oxide was absorbed by the soil and vegetation at a maximum rate of 0.31 ng NO-N m⁻² s⁻¹. The aeration state of the soil controlled the relative rates of NO and N₂O emission. Nitric oxide was the major gas emitted from well aerated soils, conditions that favour nitrification. The NO/N₂O emission ratio was >100 for the coarse-textured sandy loam soil and the clay loam soil only during low rainfall periods. Nitrous oxide was the major gas emitted from less aerated soils, conditions that allowed denitrification to occur. The NO/N₂O emission ratio was <0.001 for the clay loam soil when rainfall was high and soils were wet. Extrapolation to the U.K. situation showed that agricultural land may account for 2–6% of the total annual NO_x emission and for 16–64% of the total annual N₂O emission in the U.K.     

Polynuclear aromatic hydrocarbon degradation by heterogeneous reactions with N2O5 on atmospheric particles

The degradation of particulate polynuclear aromatic hydrocarbons (PAH) on atmospheric soot particles in the presence of gas phase dinitrogen pentoxide (N₂O₅) was explored. Dilute diesel and wood soot particles containing PAH were reacted with∼10ppm of N₂O₅ in a 200 ℓ continuous stirred tank reactor (CSTR). To provide a stable source of particles for reaction in the CSTR, diesel or wood soot particles were injected at night into a 25 m³ Teflon outdoor chamber. The large chamber served as a reservoir for the feed aerosol, and the aerosol could then be introduced at a constant flow rate into the CSTR. PAH-N₂O₅ heterogeneous rate constants for wood soot at 15°C ranged from2 × 10⁻¹⁸to5 × 10⁻¹⁸ cm³ molecules⁻¹ s⁻¹. For diesel soot the rate constants at 16°C were higher and ranged from5 × 10⁻¹⁸to30 × 10⁻¹⁸ cm³ molecules⁻¹ s⁻¹. Comparisons with other studies suggest that sunlight is the most important factor which influences PAH decay. This is followed by ozone, NO₂, N₂O₅ and nitric acid. The rate constants of nitro-PAH formation from a parent PAH and N₂O₅ were of the order of1 × 10⁻¹⁹−1 × 10⁻¹⁸ molecules⁻¹s⁻¹. The uncertainty associated with all of these rate constants is± a factor of 3. Given, however, the small magnitude of the rate constants and the low levels of N₂O₅ present in the atmosphere, we concluded that PAH heterogeneous reactions with gas phase N₂O₅ degrade particle-bound PAH or to form nitro-PAH from PAH arenot very important. (Direct application of the specific rate constants derived in this study to ambient atmospheres should not be undertaken unless the ambient particle size distributions and chemical composition of the particles are similar to the ones reported in this study.)     

Measurements of the optical properties of the smoke emissions from plastics,hydrocarbons, and other urban fuels for nuclear winter studies

We have measured the optical and microphysical properties of smoke from burning plastic materials and other components of the urban fuel mix, including hydrocarbons, rubber, and wood, to provide information on the source term for possible aerosol clouds injected into the atmosphere following large scale urban fires. Our measurements included measurements of emission factors; in situ optical measurements of aerosol absorption, scattering, and attenuation; and collection of particles using both filters and cascade impactors for size and mass concentration determinations.These measurements were made under a variety of conditions to investigate the range of variation of these optical parameters and to relate observed differences in smoke properties to differences in fuel composition and fire conditions.The plastic data show average B_e values near 10 m² g⁻¹ at 488 nm and 8 m² g⁻¹ at 633 nm. Values of B_e measured during smoldering combustion are significantly less than in flaming combustion. Flaming combustion B_e values for the rubber appear to be somewhat higher, particularly for the tire rubber; petroleum product fuel values are comparable to the plastic fuel values; and oak smoke emissions values are slightly lower than the plastic values. Measured 633 nm B_a values were approximately 6 m² g⁻¹ for the petroleum products, 7 m² g⁻¹ for the rubber, 6 m² g⁻¹ for the wood, and 6 m² g⁻¹ for the plastic.     

The variability of biogenic sulfur flux from a temperate salt marsh on short time and space scales

Three emission chambers were deployed simultaneously to measure rates of emission of dimethyl sulfide, methane thiol and carbonyl sulfide within or across vegetation zones in a New Hampshire salt marsh. Short term (a few hours) variation in fluxes of all S gases from replicate sites were small within a monospecific stand of either Spartina alterniflora or S. patens. The quantity of emergent biomass and the type of vegetation present were the primary factors regulating the rate of emission. Dimethyl sulfide fluxes from the S. alterniflora soils ranged from 800 to 18,000 nmol m⁻² h⁻¹ compared to emissions of 25–120 nmol m⁻² h⁻¹ from S. patens. This difference was probably due to the presence of the dimethyl-sulfide precursor dimethylsulfoniopropionate which is an osmoregulator in S. alterniflora but not in S. patens. Methane thiol emissions from S. alterniflora were 20–280 nmol m⁻² h⁻¹ and they displayed a similar diel trend as dimethyl sulfide, although at much lower rates, suggesting that methane thiol is produced primarily by leaves. Methane thiol emissions from S. patens were 20–70 nmol m⁻² h⁻¹. Net uptake of carbonyl sulfide of 25–40 nmol m⁻² h⁻¹ occurred in stands of S. alterniflora while net efflux of 10–36 nmol m⁻² h⁻¹ of carbonyl sulfide occurred in stands of S. patens. In general, ranges of emissions of sulfur gases were similar to most other published values.     

Three-wavelength nephelometer suitable for aircraft measurement of background aerosol scattering coefficient

A new nephelometer suitable for aircraft measurements of aerosol scattering extinction coefficient (σ_sp) has been constructed and operated under field conditions. This instrument is vacuum tight for operation in a pressurized aircraft cabin and is capable of measuring background tropospheric σ_sp at an averaging time of 1 min. For example, in a typical atmospheric profile the instrument can measure values of about 10⁻⁴ m⁻¹ with a time resolution of 2 s in a polluted region, and about 10⁻⁷ m⁻¹ with a time resolution of 1 min in a clean region. This sensitivity is made possible by: (1) subtracting in real time the air Rayleigh scattering from the total scattering signal by continuously measuring pressure and temperature in the sampling volume of the instrument; (2) correcting for the dark count and sensitivity of the photomultipliers using a rotating shutter; and (3) using a beam splitter arrangement to allow simultaneous detection by three photomultipliers. A laboratory measurement of instrument noise suggests a 550-nm noise level of about 5 × 10⁻⁸ m⁻¹ at an averaging time of 1 min.     

Atmospheric coarse particulate concentrations and dry deposition fluxes for ten metals in two urban environments

The atmospheric coarse particle concentrations of ten metals (Al, Ca, Cd, Cu, Fe, Mn, Ni, Pb, Si and Zn) were measured with the Noll Rotary Impactor (NRI) in the Los Angeles Basin (Claremont) California, and in Chicago, Illinois. The dry deposition fluxes were also measured for the ten elements at the Chicago site. An evaluation of the data demonstrates that the coarse particle mass could be divided into two categories: (1) material that was primarily of crustal origin (Al, Ca, Fe and Si) and (2) material that was primarily of anthropogenic origin (Cd, Cu, Mn, Ni, Pb and Zn). The mass of crustal material varied between 15 and 50% of the total coarse particle mass, while the mass of anthropogenic material was <1%. The dry deposition fluxes for the crustal material were between 20 (Al) and 200 (Si) ng m⁻² s⁻¹ while the fluxes for the anthropogenic material were between 1 and 7 ng m⁻¹ s⁻¹ for Cu, Mn, Pb and Zn. The cadmium (Cd) flux averaged 0.02 ng m⁻² s⁻¹.     

Seasonal contrasts in modelled and observed dry deposition velocities of O3, SO2 and NO2 over three surfaces

Results of modelled and observed deposition velocities (V_d) for O₃, SO₂ and NO₂ for time-averaged diurnal cycles and sometimes for a collection of hourly values taken from different days are discussed for different seasons. From the observations, it was found that the O₃V_d values over a deciduous forest had a daytime representative value of 1.0 cm s⁻¹ in the summer and 0.3 cm s⁻¹ in the winter. For SO₂ over the same forest and over a carrot field the daytime values ranged from 0.0 to 0.65 cm s⁻¹ in the autumn, and for SO₂ over a snow surface the V_d ranged from 0.0 to 0.15 cm s⁻¹. The NO₂V_d was mostly negative over the forest and the carrot field in the autumn and had a range of 0.0-0.15 cm s⁻¹ over snow. From the model, it was found that for the three seasons the V_d values over all the land-use types were much larger than the observations. The model could not simulate the observed negative values of the NO₂V_d. The impact of the V_d model and its modified version on the concentrations of O₃ and SO₂ were tested with a comprehensive Eulerian air quality model.     

Real-time,in situ measurements of atmospheric optical absorption in the visible via photoacoustic spectroscopy—IV. Visibility degradation and aerosol optical properties in Los Angeles

Aerosol light absorption (b_abs) has been measured in real-time in Los Angeles with a validated photoacoustic technique, and its impact on visibility degradation has been examined. These measurements were collected during ten days in the summer of 1987 for the Southern California Air Quality Study (SCAQS). Aerosol b_abs (λ = 514.5 nm) varied from an hourly average value of 7 × 10⁻⁶ m⁻¹ in the 3–4 and 4–5 a.m. periods of 13 July to 9 × 10⁻⁵ m⁻¹ in the 7–8 a.m. period of both 28 August and 3 September. This b_abs, which is due solely to elemental carbon (EC) showed a distinct diurnal pattern with low values at night, increasing around sunrise to higher values through mid-afternoon. Comparison of these data with aerosol light scattering data clearly illustrates that the contribution of aerosol light absorption to visibility degradation increases in importance under less polluted conditions. Other urban and rural studies show similar results.     

Soil crust formation by dust deposition at Shaartuz,Tadzhik, S.S.R.

The shrub-steppe area near Shaartuz, Tadzhik, S.S.R., is shown to be a net accumulator of dust despite being an occasional source of dust. For the accumulation of the dust to form the observed surface crust, a net deposition of about 290–490 g m⁻² yr⁻¹ of particles smaller than 20 μm is required, depending on the duration of the deposition period. The particles smaller than 20 μm are mixed with particles brought up from the sandy material below the surface crust by bioturbation and are incorporated into the surface crust. Measurements during the 16 and 20 September 1989 dust storms provided a total deposition of 41.1 g m⁻² of particles smaller than 20 μm. Because 10–30 dust storms are observed at Shaartuz, the measured average dust storm deposition would yield 206–617 g m⁻² yr⁻¹. This range of deposition is of the order of that needed to provide a mass balance for the observed crust formation. Cryptogams (including algae, lichen, and moss) and rainwater are the main agents of incorporation of the aeolian dust into a stable soil crust. The role that the vascular plants played at the Shaartuz site was to reduce the rate of soil movement to levels where the cryptogamic crusting was possible. the observed mechanisms of dust deposition followed by crust incorporation are possibly an important processes in loess formation in Central Asia.     

Heterogeneous sulfur conversion in sea-salt aerosol particles: the role of aerosol water content and size distribution

Meteorological and chemical conditions during the July 1988 Bermuda-area sampling appear to have been favorable for conversion of sulfur gases to particulate excess sulfate (XSO₄). Observed average XSO₄ and SO₄ concentrations of 11 and 2.1 nmol m⁻³, respectively, at 15 m a.s.l. in the marine boundary layer (MBL) upwind of Bermuda, indicate that conversion of SO₂ to XSO₄, over and above homogeneous conversion, may be necessary to explain the > 5.0 average molar ratio of XSO₄ to SO₂. Given an observed cloud cover of <15% over the region and the <3 nmol m⁻³ SO₃ concentrations observed by aircraft, heterogeneous conversion mechanisms, in addition to cloud conversion of SO₂, are necessary to explain the observed 11 nmol XSO₄ m⁻³.Aerosol water content, estimated as a function of particle size distribution plus consideration of SO₂ mass transfer for the observed particle size distribution, shows that SO₂ was rapidly transferred to the sea-salt aerosol particles. Assuming that aqueous-phase SO₂ reaction kinetics within the high pH sea-salt aerosol water are controlled by O₃ oxidation, and considering mass-transfer limitations, SO₂ conversion to XSO₄ in the sea-salt aerosol water occurred at rates of approximately 5% h⁻¹ under the low SO₂ concentration, Bermuda-area sampling conditions. All of the 2 nmol XSO₄ m⁻³ associated with sea-salt aerosol particles during low-wind-speed, Bermuda-area sampling can be explained by this conversion mechanism. Higher wind speed, greater aerosol water content and higher SO₂ concentration conditions over the North Atlantic are estimated to generate more than 4 nmol XSO₄ m⁻³ by heterogeneous conversion of SO₂ in sea-salt aerosol particles.     

Rate constants for the gas-phase reactions of OH and NO3 radicals and O3 with sabinene and camphene at 296±2 K

The rate constants for the gas-phase reactions of sabinene and camphene, two monoterpenes emitted from vegetation, with OH and NO₃ radicals and O₃ have been determined at 296±2 K and one atmosphere total pressure of air. The OH and NO₃ radical reaction rate constants were determined using relative rate techniques. Using rate constants of k(OH + isoprene) = 1.01 × 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹, k(NO₃ + trans-2-butene) = 3.87 × 10⁻¹³ cm³ molecule⁻¹ s⁻¹ and k(NO₃ + 2-methyl-2-butene) = 9.33 × 10⁻¹² cm³ molecule⁻¹ s⁻¹, the following OH and NO₃ radical reaction rate constants (in cm³ molecule⁻¹ s⁻¹ were obtained: OH radical reaction; sabinene, 1.17 × 10⁻¹⁰ and camphene, 5.33 × 10⁻¹¹; NO₃ radical reaction; sabinene, 1.01 × 10⁻¹¹, and camphene, 6.54 × 10⁻¹³. The absolute O₃ reaction rate constants determined were (in cm³ molecule⁻¹ s⁻¹ units): sabinene, 8.07 × 10⁻¹⁷, and camphene, 9.0 × 10⁻¹⁹. These rate constants are compared to literature data for other structural-related alkenes and monoterpenes.     

Modified ADM1 for modeling free ammonia inhibition in anaerobic acidogenic fermentation with high-solid sludge

Anaerobic acidogenic fermentation with high-solid sludge is a promising method for volatile fatty acid (VFA) production to realize resource recovery. In this study, to model inhibition by free ammonia in high-solid sludge fermentation, the anaerobic digestion model No. 1 (ADM1) was modified to simulate the VFA generation in batch, semi-continuous and full scale sludge. The ADM1 was operated on the platform AQUASIM 2.0. Three kinds of inhibition forms, e.g., simple inhibition, Monod and non-inhibition forms, were integrated into the ADM1 and tested with the real experimental data for batch and semi-continuous fermentation, respectively. The improved particle swarm optimization technique was used for kinetic parameter estimation using the software MATLAB 7.0. In the modified ADM1, the K_s of acetate is 0.025, the k_m,ac is 12.51, and the K_{I_NH3} is 0.02, respectively. The results showed that the simple inhibition model could simulate the VFA generation accurately while the Monod model was the better inhibition kinetics form in semi-continuous fermentation at pH 10.0. Finally, the modified ADM1 could successfully describe the VFA generation and ammonia accumulation in a 30 m³ full-scale sludge fermentation reactor, indicating that the developed model can be applicable in high-solid sludge anaerobic fermentation.     

Physicochemical damage parameters for the action of SO2 and NO2 on single pieces of marble

The theoretical analysis for measurement of building-damage parameters by RF-GC technique is applied to the action of SO₂ and NO₂ on marble. The experiments with SO₂ were performed with five different geometric forms of single pieces of marble at 373.2 K and were repeated after washing these pieces 8 times with three-distilled water. All six physicochemical parameters determined show negligible variations for the same solid form at the same temperature, but they are different for the various geometrical forms. The mass transfer coefficients K_g and K_s and their ratio K seem to be the most invariant parameters with respect to the form. After washing with water, some of the parameters change considerably.The action of NO₂ was studied on a sphere only, but at five different temperatures. The physicochemical parameters for the action of this gas are three orders of magnitude smaller than those of SO₂ (except K), leading to 3700 times bigger resistance of marble to mass transfer of NO₂ than of SO₂. From the variation of the parameters with temperature, it is concluded that both mass transfer coefficients, K_g and K_s, pertain to activated processes with activation energies 39 and 27 kJ mol⁻¹, respectively. The reaction of the adsorbed gas with the solid is less activated, whereas the adsorption equilibrium constant K does not change with temperature.     

Wind tunnel experiments on the resuspension of particulate material

A programme of wind tunnel experiments has been carried out in which the resuspension of particulate material of four sizes (4, 10, 18 and 22 μm diameter) from concrete and grass surfaces has been studied. The importance of wind speed has been investigated and the time dependence of the resuspension rate has been evaluated for periods shortly after the onset of resuspension. The results indicate rapidly falling values of the resuspension rate which are approximately related to 1/time. The increase in the resuspension rate with increasing wind speed was most pronounced for large particles, leading to the conclusion that resuspension can be dominated by short-duration episodes which coincide with conditions that favour resuspension. Resuspension rates, averaged over approximately 1 h after the onset of conditions leading to resuspension, were in the range 1 × 10⁻⁶ to 5 × 10⁻⁶ s⁻¹, at moderate wind speeds (less than 5 m s⁻¹), with little difference between the grass and concrete surfaces. For high wind speeds (greater than 6.5 m s⁻¹), several per cent of the total surface deposit of 22 μ diameter particles was removed from both the concrete and grass surfaces within 10 s of the onset of wind.     

The effect of freezing on the composition of supercooled droplets—II. Retention of S(IV)

S(IV) dissolved in droplets is partially evolved as SO₂ during freezing. A spray of droplets with average diameter 39μm, produced by an ultrasonic transducer, was let to fall through a controlled atmosphere with known SO₂ concentration, at varying temperatures between −8 and −23°C, attaining thermal and chemical equilibrium. In a first arrangement, the droplets fell by gravitation on an ice surface. Two other arrangements simulated the riming ventilation conditions: in one series of experiments, the droplets were projected by a gas jet at several m s⁻¹ against a target; in another, the droplets were caught by rotating rods. The fraction of S(IV) retained in the ice Γ was determined by analysis of the samples and comparison with the equilibrium concentration in the liquid droplets. Samples collected by gravitation showed a retention coefficient Γ = 0.25 + 0.012 T_s (T_s = supercooling); rime samples showed large dispersion in the results, the retention coefficient being best represented by an average value Γ = 0.62, independent of temperature.     

An efficient absorbing system for spectrophotometric determination of nitrogen dioxide

A simple and sensitive spectrophotometric method for determination of atmospheric nitrogen dioxide using o-nitroaniline as an efficient absorbing, as well as diazotizing, reagent is described. o-Nitroaniline present in the absorbing medium is diazotized by the absorbed nitrite ion to form diazonium compound. This is later coupled with 1-amino-2-naphthalene sulphonic acid (ANSA) in acidic medium to give red-violet-coloured dye,having λ_max = 545 nm. The isoamyl extract of the red azo dye has λ_max = 530 nm. The proposed reagents has ≈ 100% collection efficiency and the stoichiometric ratio of NO₂:NO₂⁻ is 0.74. The other important analytical parameters have been investigated. By employing solvent extraction the sensitivity of the reaction was increased and up to 0.03 mg m⁻³ nitrogen dioxide could be estimated.