The nonlinearity and related band strength of carbon monoxide when applied in ambient air measurement using open long-path Fourier transform infrared spectrometry

The accuracy of CO concentration determination by open-path Fourier transform infrared (FTIR) spectrometry has been re-evaluated in detail. The evaluation focuses on the correction of the calibration curve--the integrated intensity of a standard spectrum--that is used as a comparison spectrum when doing quantitative analysis of CO. Results show that the calibration curve (with 0.5 cm(-1) or 1 cm(-1) resolution) is apparently inclined to be nonlinear under standard conditions, and that the threshold point of nonlinearity is approximately 0.1 atm-cm. Two commercial FTIR field monitoring systems have been used to investigate the nonlinearity trend. The experimental method consists of using open-path FTIR systems in combination with nondispersive infrared (NDIR) monitors to establish the calibration curve in a semi-closed corridor The results have been double-checked using closed-cell dynamic equilibrium systems. When the optical density is larger than a certain value, the curves begin to bend, and when the optical density approaches zero, the band strength is around 178 +/- 3 atm(-1) cm(-2) and 173 +/- 2 atm(-1) cm(-2), respectively, for 0.5 and 1 cm(-1) resolution at standard temperature and pressure (STP). These values are quite different from other published data that have been acquired by the pressurized method or by high-resolution (<0.006 cm(-1)) spectrometers. It is thought that a higher accuracy is achieved when these new calibration results are used to quantify the CO concentration. The error in concentration determination within 0.1 optical density is less than 2%, and that in the higher optical density region is less than 5%.     

Combined measurements of thermal emission and solar absorption of atmospheric carbon monoxide

A new technique using ground-based FTIR spectroscopy has been developed to investigate the vertical distribution of carbon monoxide in the atmosphere. Complementary measurements of atmospheric emission and solar absorption over the infrared region have been carried out sequentially to determine the amounts of carbon monoxide in the lower and upper atmosphere. The method is based on the fact that the two techniques of remote sensing are inherently sensitive to the carbon monoxide amount in different regions of the atmosphere. The measurements have been made under summertime conditions at a northern mid-latitude rural setting with a relatively pollution-free atmosphere. The total zenith column amount was determined to be 1.84×10¹⁸ molecules cm^-2±7% which was based on the solar absorption measurement. From the analysis of the thermal emission spectrum, which is sensitive to carbon monoxide only in the lower troposphere, a zenith column amount of 1.01×10¹⁸ molecules cm^-2±10% was estimated for the first 4.8 km of the atmosphere; this corresponded to an average carbon monoxide mixing ratio of 118 ppbv. Comparing the results of the two measurements indicated that a zenith column amount 8.3×10¹⁷ molecules cm^-2±20%, or an average mixing ratio of 66 ppbv, was present in the free troposphere above an altitude of 4.8 km. These results are consistent with those reported for other northern mid-latitude locations using various in situ and solar absorption measuring techniques.     

Carbon monoxide photoproduction from rice and maize leaves

We investigated CO photoproduction from intact leaves of rice (Oryza sativa L.) and maize (Zea mays L.) by laboratory experiments. CO photoproduction showed positive correlation with light intensity and was positively dependent on oxygen concentration. The average CO photoproduction was 2.6±0.3×10¹⁰ molecules cm⁻² s⁻¹ from rice leaves and 2.2±0.1×10¹⁰ molecules cm⁻² s⁻¹ from maize leaves (n=5) at a radiation intensity of 49 mW cm⁻². CO photoproduction from senescent rice leaves was 9 times greater (25.7±1.5×10¹⁰ molecules cm⁻² s⁻¹, n=2) at the same radiation intensity than from live leaves, and responded slowly to changes in oxygen concentration and light intensity. CO photoproduction showed no correlation with CO₂ concentration or humidity. This indicates that CO photoproduction in leaves is not directly controlled by carbon metabolism or stomatal conductance. The lack of dependence on stomatal conductance leads to the conclusion that the diffusion of CO from inside the leaves to the atmosphere is not a controlling factor for CO photoproduction from rice and maize leaves.     

Measurement of ammonia emissions using various techniques in a comparative tunnel study

A field-based intercomparison study for ammonia measurements was conducted using seven analytical methods. It included sulphuric acid impinger, citric acid denuder, differential optical absorption spectroscopy (DOAS), Fourier transform infrared spectroscopy (FTIR), photoacoustic spectroscopy (PAS), and continuous aqueous extraction followed by measurement of conductivity (Airrmonia). Measurements were done at the entrance and the exit of the Gubrist highway tunnel near Zurich, Switzerland. For DOAS, FTIR, PAS and Airrmonia, 24 hour means were calculated based on a time resolution of 10 minutes. At the tunnel exit, all 24 hour averages were within 13%, and the continuous data of the time-resolved methods agreed well. At the tunnel entrance, a slightly reduced method comparison included four methods, and daily mean values agreed within 23%. Ammonia emission factors, based on 4 weeks of continuous measurements with the Airrmonia, were 31 ± 4 mg km^-1 for light-duty vehicles and 14 ± 7 mg km^-1 for heavy-duty vehicles.     

Optical Measurements of Aerosol Size Distributions in Great Smoky Mountains National Park: Dry Aerosol Characterization

ABSTRACT

Aerosol size distributions were measured during the summertime 1995 Southeastern Aerosol and Visibility Study (SEAVS) in Great Smoky Mountains National Park using an Active Scattering Aerosol Spectrometer (ASASP-X) optical particle counter. We present an overview of the experimental method, our data inversion technique, timelines of the size distribution parameters, and calculations of dry accumulation mode aerosol density and refractive index. Aerosol size distributions were recorded during daylight hours for aerosol in the size range 0.1 < Dp < 2.5 u,m. The particle refractive index used for the data inversion was calculated with the partial molar refractive index approach using 12-hr measured aerosol chemical composition. Aerosol accumulation mode volume concentrations ranging from 1 to 26 u,m³ cm^-3 were observed, with an average of 7 ± 5 u,m³ cm^-3. The study average dry accumulation mode geometric volume median diameter was 0.27 ± 0.03 u,m, and the mean geometric standard deviation was 1.45 ± 0.06. Using an internally mixed aerosol model, and assuming chemical homogeneity across the measured particle distribution, an average accumulation mode dry sulfate ion mass scattering efficiency of 3.8 ± 0.6 m² g^-1 was calculated.     

Differences in airborne particle and gaseous concentrations in urban air between weekdays and weekends

Airborne particle number concentrations and size distributions as well as CO and NO_x concentrations monitored at a site within the central business district of Brisbane, Australia were correlated with the traffic flow rate on a nearby freeway with the aim of investigating differences between weekday and weekend pollutant characteristics. Observations over a 5-year monitoring period showed that the mean number particle concentration on weekdays was (8.8±0.1)×10³ cm⁻³ and on weekends (5.9±0.2)×10³ cm⁻³—a difference of 47%. The corresponding mean particle number median diameters during weekdays and weekends were 44.2±0.3 and 50.2±0.2 nm, respectively. The differences in mean particle number concentration and size between weekdays and weekends were found to be statistically significant at confidence levels of over 99%. During a 1-year period of observation, the mean traffic flow rate on the freeway was 14.2×10⁴ and 9.6×10⁴ vehicles per weekday and weekend day, respectively—a difference of 48%. The mean diurnal variations of the particle number and the gaseous concentrations closely followed the traffic flow rate on both weekdays and weekends (correlation coefficient of 0.86 for particles). The overall conclusion, as to the effect of traffic on concentration levels of pollutant concentration in the vicinity of a major road (about 100 m) carrying traffic of the order of 10⁵ vehicles per day, is that about a 50% increase in traffic flow rate results in similar increases of CO and NO_x concentrations and a higher increase of about 70% in particle number concentration.     

Determination of Room Temperature OH Rate Constants for Acetylene,Ethylene Dichloride,Ethylene Dibromide,p-Dichlorobenzene and Carbon Disulfide

A relative rate procedure was used to measure hydroxyl rate constants at room temperature in the presence of oxygen. The photolysis of methyl nitrite in the presence of nitric oxide was used to generate OH radicals. The rate of loss of the test compounds was measured relative to that of ethane (k_OH = 2.74 × 10^-13 cm³ molec^-1 s^-1). The rates obtained at 297 ± 2 K are: acetylene = (7.8 ± 1.6) × 10^-13 cm³ molec^-1 s^-1,1,2-dichloroethane (2.8 ± Q.6) × 10^-13 cm³ molec^-1 s^-1, 1,2-dibromoethane (2.4 ± 0.5) × 10^-13 cm³ molec^-1 s^-1, p-dichlorobenzene (4.3 ± 0.9) × 10^-13 cm³ molec^-1 s^-1 and carbon disulfide (29 ± 6) × 10^-13 cm³ molec^-1 s^-1. Under a proposed EPA rule, this OH rate determination procedure could be used to determine if a given volatile organic will be subject to control for reduction of photochemical ozone.     

Spatial distribution of submicrometre particles and CO in an urban microscale environment

Traffic is the major source of submicrometre particles in an urban environment but the spatial distribution of particles around an urban site has not been measured. The aim of this paper was to investigate the relationship of CO and particles at a busy central urban location surrounded by buildings. This study measured the concentration and size distribution of submicrometre particles at a fixed location and concentrations of submicrometre particles and CO at 10 locations around a square site in the Brisbane Central Business District (CBD). Changes in concentration were assessed as a function of traffic volume and wind direction and speed.Fixed site measurements of submicrometre particle number concentration varied between 7.9×10² (±40) and 2.6×10⁵ (±1.3×10⁴) cm⁻³ and showed a strong positive correlation with traffic flow rate, confirming that vehicles were the major source of urban submicrometre particles. The particle concentration decreased exponentially with increasing wind speed.Average particle concentrations around the site ranged between 19.7×10³ (±8.2×10³) and 32.5×10³ (±16.6×10³) cm⁻³. Analysis of the particle measurements around the site showed that time and location both had a statistically significant effect on mean particle concentration around the square over the period of the study.Around the site, CO concentration was relatively constant (within instrument error), ranging between 2.2 (±1.9) and 4.5 (±3.0) ppm. Again both time and location had a statistically significant effect on CO concentration during the measurement period. However, CO concentration was not significantly correlated to particle number concentration around the site and examination of between-site comparisons with the two pollutants showing different spatial and temporal trends.The significant difference in the concentration trends between the locations around the square indicates that there is considerable inhomogeneity in the particle concentration around the site. One implication of this is that careful thought must be given to locations of air intakes of air-conditioning systems in urban environments.     

The rate and mechanism of the gas-phase oxidation of hydroxyacetone

The rate and mechanism for gas-phase destruction of hydroxyacetone, CH₃C(O)CH₂OH, by reaction with OH, Cl-atoms, and by photolysis have been determined. The first quantitative UV absorption spectrum of hydroxyacetone is reported over the wavelength range 235 to 340 nm; the spectrum is blue-shifted by about 15 nm relative to that of acetone and peaks at 266 nm, with a maximum absorption cross section of (6.7±0.6) ×10^-20 cm² molecule^-1. Measurable absorption extends out to about 330 nm. The quantum yield for photolysis of hydroxyacetone in the region relevant to the troposphere (λ>290 nm) was found to be significantly less than unity. Rate coefficients for the reaction of hydroxyacetone with OH radicals and Cl-atoms were determined at 298 K using the relative rate technique. The rate coefficient for reaction with OH was found to be (3.0±0.7)×10^-12 cm³ molecule^-1 s^-1, while the rate coefficient for reaction with Cl-atoms was found to be (5.6±0.7)×10^-11 cm³ molecule^-1 s^-1. Both values agree well with previous studies. The data were used to determine the lifetime of hydroxyacetone in the troposphere. Reaction with OH is the major gas-phase destruction mechanism for this compound, limiting its lifetime to about 4 days, while photolysis is found to be only of minor importance.     

The In-Plume Emission Test Stand: An Instrument Platform for the Real-Time Characterization of Fuel-Based Combustion Emissions

Abstract

The In-Plume Emission Test Stand (IPETS) characterizes gaseous and particulate matter (PM) emissions from combustion sources in real time. Carbon dioxide (CO₂), carbon monoxide (CO), nitric oxide (NO), nitrogen dioxide (NO₂), and other gases are quantified with a closed-path Fourier transform infrared spectrometer (FTIR). Particle concentrations, chemical composition, and other particle properties are characterized with an electrical low-pressure impactor (ELPI), a light-scattering particle detector, an optical particle counter, and filter samples amenable to different laboratory analysis. IPETS measurements of fuel-based emission factors for a diesel generator are compared with those from a Mobile Emissions Laboratory (MEL). IPETS emission factors ranged from 0.3 to 11.8, 0.2 to 3.7, and 22.2 to 32.8 g/kg fuel for CO, NO₂, and NO, respectively. IPETS PM emission factors ranged from 0.4 to 1.4, 0.3 to 1.8, 0.3 to 2.2, and 1 to 3.4 g/kg fuel for filter, photoacoustic, nephelometer, and impactor measurements, respectively. Observed linear regression statistics for IPETS versus MEL concentrations were as follows: CO slope = 1.1, r² = 0.99; NO slope = 1.1, r² = 0.92; and NO₂ slope = 0.8, r² = 0.96. IPETS versus MEL PM regression statistics were: filter slope = 1.3, r² = 0.80; ELPI slope = 1.7, r² = 0.87; light-scattering slope = 2.7, r² = 0.92; and photoacoustic slope = 2.1, r² = 0.91. Lower temperatures in the dilution air (~25 °C for IPETS vs. ~50 °C for MEL) may result in greater condensation of semi-volatile compounds on existing particles, thereby explaining the 30% difference for filters. The other PM measurement devices are highly correlated with the filter, but their factory-default PM calibration factors do not represent the size and optical properties of diesel exhaust. They must be normalized to a simultaneous filter measurement.     

Rate Constants for the Reaction of OH with Halocarbons in the Presence of O2 + N2

Rates of CO₂ production in the reaction CO + OH and CO + OH + halocarbon have been used to determine rate constants for some OH + halocarbon reactions at 29.5°C relative to that of k(CO + OH) = 2.69 × 10^?13 cm³ molecule^?1 sec^?1. The following rate constants were obtained: k(OH + CH₃Cl) = 3.1 ± 0.8, k(OH + CH₂Cl₂) = 2.7 ± 1.0, k(OH + C₂H₅Cl) = 44.0 ± 25, k(OH + CICH₂CH₂CI) = 6.5, (<29) and k(OH + CH₃CCl₃) = 2.1 (<5.7) cm³ molecule^?1 sec^?1 × 10^?14. The k values, CH₂Cl₂ excepted, are in substantial agreement with determinations made in nonoxygen environments. The present results for CH₂Cl₂ are almost certainly in error due to difficulties with the competitive approach used.     

Evidence of acid–base interactions between amines and model indoor surfaces by ATR-FTIR spectroscopy

Molecular associations of pyridine with cellulose and gypsum, surrogates for common indoor surface materials, were studied using an attenuated total reflection (ATR)-Fourier transform infrared (FTIR) spectrophotometric method. The purpose of this study was to gain insight into the molecular interactions of amines with well-characterized materials that affect their partitioning between indoor air and surfaces. The experimental results suggest the presence of at least two sorptive states for volatile and semivolatile amines, attributed to the chemisorbed species and to a more labile surface state (i.e., physisorbed pyridine). Both exhibited spectroscopic signatures corresponding to aromatic C–H stretching modes (2950–3100 cm⁻¹) in the studied spectral region. Chemisorbed pyridine could be identified by the presence of additional IR signals in the N–H and O–H stretching region of the spectrum (2900–3600 cm⁻¹). During desorption under a stream of N₂, surface enrichment in the chemisorbed species was evidenced by a slower reduction of the absorbance of the broad band at 2900–3600 cm⁻¹ in relation to the total pyridine absorbance change. This spectroscopic evidence for acid–base interactions between amines and surfaces is consistent with the desorption behavior observed in previous work for nicotine from model surfaces.     

Technical Session Preliminary Schedule Announced for 1988 APCA Annual Meeting

ABSTRACT

Stable heterogeneous catalysts for the oxidative removal of CO from air at ambient temperatures have been developed. An alumina support impregnated with PdCl₂, CuCl₂, and CuSO₄ is described. Optimal activity was obtained with Pd 0.020 mol/kg, Cu 0.50 mol/kg, CuCl₂ 20-30% of total Cu, a 2- to 24-hr soak, filtration of surplus raffinate, and a 2- to 4-hr firing in air at 200-350 °C. The catalysts are effective at 20-26 °C and relative humidities in the 15-90% range. They are reversibly deactivated by completely dry or water-saturated air streams. These catalysts have been tested at space velocities up to 30,000 hr^-1. In contact with <100 ppm CO, they are highly efficient, removing ~99% of the CO with contact times of ~120 msec (pseudo-first order k' > 25 sec^-1). At much higher CO concentrations, the maximum CO loading rate—limited by the Cu(I) reoxidation rate—is approximately 17 m mol CO per Limol Pd per hour.     

The radiative efficiency of HCF2OCF2OCF2CF2OCF2H (H-Galden 1040x) revisited

The infrared spectrum of HCF₂OCF₂OCF₂CF₂OCF₂H (CAS# 188690-77-9) has been re-measured. The integrated absorption intensity over the range 1000–1500 cm^?1 measured in the present work is (6.65 ± 0.33) × 10^?17 cm² molecule^?1 cm^?1 in 700 Torr of air at 296 K. The radiative efficiency of HCF₂OCF₂OCF₂CF₂OCF₂H is calculated to be 1.02 W m^?2 ppb^?1. The value reported in the 2007 Intergovernmental Panel on Climate Change (IPCC) report is approximately 35% larger reflecting what we believe to be an erroneously high value for the absorption strength of HCF₂OCF₂OCF₂CF₂OCF₂H adopted by the IPCC.     

Henry's Law coefficients of chloropicrin and methyl isothiocyanate

Henry's Law coefficients were measured for the first time for chloropicrin and methyl isothiocyanate (MITC) at 25 °C in deionized water, in 0.10 M NaCl, in 0.20 M NaCl, and in pH 4.0 and 8.0 buffered solutions. For chloropicrin, the Henry's Law coefficient was 2.1±0.3 atm M⁻¹, and did not show significant pH dependence or dependence on ionic strength. For MITC, the coefficient was much smaller, 0.06±0.05 atm M⁻¹. The Henry's Law coefficient for MITC did show dependence on ionic strength, increasing to 0.14±0.05 atm M⁻¹ at 0.20 M, but did not appear to depend on pH. MITC has a much stronger tendency to remain in solution than chloropicrin. The transport of chloropicrin from solution to the atmosphere is likely to be significant environmentally, while MITC shows a much lower rate of volatilization. When transferred to the atmosphere, oxidation and photochemical reactions are likely to dominate the transformation of both chloropicrin and MITC, rather than heterogenous reactions.     

改进GC/FID法连续观测大气中CO浓度

改进装配有氢火焰离子化检测器(即FID)的气相色谱仪(GC),可连续监测大气中痕量气体CO浓度.本系统采用单阀双柱反吹进样技术,优选前置柱能更有效地剔除杂质,提高了分析柱效率,保持色谱基线平稳,提高分辨率和定量分析的准确率.优化后的气路设计与色谱柱的改进,使GC/FID对CO的最低检出限达到10×10-9、精密度误差小于2%,准确度在±2%之内.将气相色谱与动态气体稀释仪耦合使系统能够自动进行工作曲线校准,系统自动采样、分析和标定,无需人员职守.对北京大气CO连续观测结果表明,北京大气CO浓度变化受气象要素与排放源双重控制.     

Copper chitosan nanocomposite: synthesis, characterization, and application in removal of organophosphorous pesticide from agricultural runoff

Purpose

Removal of malathion from agricultural runoff was studied using novel copper-coated chitosan nanocomposite (CuCH)??a biopolymeric waste obtained from marine industry.

Methods

Synthesis and characterization of the adsorbent using different spectral techniques like Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy, energy-dispersive X-ray spectroscopy, Brunauer, Emmett, and Teller surface analyzer have been carried out. Equilibrium studies have been carried out to optimize the dose rate, pH, and the reaction time. Parathion and methyl parathion removal were also evaluated by CuCH in the batch mode. Using gas chromatography?Cmass spectrometry (GC?CMS) and FTIR studies suitable mechanism for adsorption has been suggested.

Results

The particle size of the adsorbent ranged from 700 to 750?nm. The surface area was found to be 20?m²?g^-1 with a pore volume of 0.11?cc?g^-1. The maximum adsorption capacity of malathion by CuCH was found to be 322.6?±?3.5?mg?g^-1 at an optimum pH of 2.0. Presence of copper ions enhanced the adsorption capacity of the adsorbent. The reaction was found to follow pseudo second-order kinetics with a rate constant of 0.53?g?mg^-1?min^-1. Evidence from FTIR indicated that copper ions form a dithionate complex with malathion during the adsorption stage. The adsorbent was found to remove malathion completely from spiked concentration of 2?mg?l^-1 in the agricultural run-off samples. It was also found that CuCH removed other organophospurous pesticides like methyl parathion and parathion under prevailing conditions.

Conclusions

The results indicated that CuCH could be applied for the removal of organophosphorous pesticides.     

Characterization of the Sunset Semi-Continuous Carbon Aerosol Analyzer

Abstract

The field-deployable Sunset Semi-Continuous Organic Carbon/Elemental Carbon (Sunset OCEC) aerosol analyzer utilizes the modified National Institute for Occupational Safety and Health thermal-optical method to determine total carbon (TC), organic carbon (OC), and elemental carbon (EC) at near real-time. Two sets of OC and EC are available: thermal OC and EC, and optical OC and EC. The former is obtained by the thermal-optical approach, and the latter is obtained by directly determining EC optically and deriving optical OC from TC. However, the performance of the Sunset OCEC is not yet fully characterized. Two collocated Sunset OCEC analyzers, Unit A and Unit B, were used to determine the pooled relative standard deviation (RSD) and limit of detection (LOD) between September 18 and November 6, 2007 in Richland, WA. The LOD of Unit A was approximately 0.2 μgC/m³ (0.1 μgC/cm²) for TC, optical OC, and thermal OC, and 0.01 μgC/m³ (0.01 μgC/cm²) for optical EC. Similarly, Unit B had an LOD of approximately 0.3 μgC/m³ (0.2 μgC/cm²) for TC, optical OC, and thermal OC, and 0.02 μgC/m³ (0.01 μgC/cm²) for optical EC. The LOD for thermal EC is estimated to be 0.2 μgC/m³ (0.1 μgC/cm²) for both units. The pooled RSDs were 4.9% for TC (carbon mass loadings 0.6–6.0 μgC/cm²), 5.6% for optical OC (carbon mass loadings 0.6–5.4 μgC/cm²), 5.3% for thermal OC (carbon mass loadings 0.6–5.3 μgC/cm²), and 9.6% for optical EC (carbon mass loadings 0–1.4 μgC/cm²), which indicates good precision between the instruments. The RSD for thermal EC is higher at 24.3% (carbon mass loadings 0–1.2 μgC/cm²). Low EC mass loadings in Richland contributed to the poor RSD of EC. The authors found that excessive noise from the nondispersive infrared (NDIR) laser in the Sunset OCEC analyzer could result in a worsened determination of OC and EC. It is recommended that a “quieter” NDIR laser and detector be used in the Sunset OCEC analyzer to improve quantification. Future work should re-evaluate the precision of the EC parameters in an environment favorable for EC collection. Investigation among quantification differences using various thermal-optical protocols to determine OC and EC is also in need.     

SO2 emission measurement with the European standard reference method,EN 14791, and alternative methods – observations from laboratory and field studies

EN 14791 is a European Standard Reference method for the measurement of SO₂ in emissions. This standard is based on a wet-chemical method in which SO₂ present in flue gases is absorbed into an absorption solution containing hydrogen peroxide, and analyzed as sulfates after sampling. This study presents the results obtained when three portable automated measuring systems (P-AMS), based on Fourier-transform infrared (FTIR) spectroscopy, non-dispersive infrared (NDIR) and ultraviolet-fluorescence (UV) techniques, were compared to the Standard Reference Method for SO₂ (EN 14791) in order to verify whether they could be used as alternative methods (AM) to EN 14791. In the case of FTIR, the measurements were performed from hot and wet gas, without any conditioning. UV-fluorescence analyzers were equipped with dilution probes and one NDIR applied a permeation dryer, whereas the other had a chiller. Tests were carried out at concentration ranges from 0 to 200 mg/m³(n) and from 0 to 800 mg/m³(n) for testing of equivalency according to CEN/TS 14793 using a test bench. Equivalency test criteria were met for all tested P-AMS except for NDIR at the lower range. The SO₂ results measured with NDIR and the chiller were lower compared to the set-up with NDIR and permeation. This was most probably due to the chiller causing absorption of SO₂ in the condensate. Tests were also carried out at field conditions, measuring the SO₂ emissions from a boiler combusting mainly bark. The same phenomena were observed in these tests as during the test bench study, i.e. the measurement set-up with NDIR and the chiller gave the lowest results. These data demonstrated that the tested alternative methods (FTIR, UV-fluorescence, and NDIR) could be used instead of the standard reference method EN 14791, thus providing real-time calibration of automated measuring systems. It must however be emphasized that when measuring water-soluble gases, such as SO₂, the choice of suitable conditioning technique is critical in order to minimize losses of the studied component in the condensate.

Implications: Portable automated measuring systems (P-AMS) provide real-time information about emissions and their concentrations, thus offering significant advantages compared to wet-chemical methods. This study presents results which can be used as a validation protocol to show that the tested P-AMS techniques (FTIR, NDIR, UV-fluorescence) could be used instead of EN 14791 (CEN 2017a) as alternative methods (AM), when paying attention to the selection of an appropriate conditioning technique.     

Measuring chemical emissions using open-path Fourier transform infrared (OP-FTIR) spectroscopy and computer-assisted tomography

This paper reports on a field study that was part of a large-scale, multi-seasonal research study with the North Carolina Department of Environment, Health, and Natural Resources, to measure nitrogen emissions from an intensive swine confinement facility. The study measured emission rates using tracer gases and a horizontal network of open-path Fourier transform infrared (FTIR) optical rays placed less than a meter above the surface of an approximately 6 acre intensive swine waste lagoon in Eastern North Carolina. This network of rays simultaneously monitored the ammonia and the tracer gases every 2 min. The open-path measurements were combined with the mathematical mapping techniques of computer-assisted tomography (CAT) to create two-dimensional concentration maps of the gases for the entire lagoon surface. For this study, a ratioing technique was applied to the tomographic concentration maps to estimate the nitrogen emission rates (from ammonia) using known tracer emission rates. The average concentrations of ammonia measured in August, November, and May were 0.81, 0.25, and 0.74 ppm, respectively. In general, ammonia concentrations were lowest at the center of the lagoon and could vary across a lagoon from 2 to 4 times depending upon the time of the day and the meteorological conditions. Emission rates were only calculated for November and May, up until midnight. In November 1997, the average flux was 1910 μg N m⁻²-min⁻¹ (range 542–4695 μg N m⁻²-min⁻¹) and in May the average flux was 4775 μg N m⁻²-min⁻¹ (range 2572–8499 μg N m⁻²-min⁻¹). This study was important because it not only provided nitrogen emission rate measurements using a new technology which can measure concentrations over large areas in real time, it was the first large-scale outdoor field study using this application.