The annual variation in stomatal ammonia compensation point of rye grass (Lolium perenne L.) leaves in an intensively managed grassland

The stomatal ammonia compensation point for ammonia (NH₃) of an intensively managed pasture of rye grass (Lolium perenne L.) was followed from mid January till November 2000. Leaf samples were taken every week. Simultaneously, the ambient NH₃ concentration was measured. Meteorological data (temperature, wind speed, rainfall and radiance) were collected from a nearby field station. The vacuum infiltration technique was used to isolate the apoplastic solution of the leaves. From the determined ammonium (NH₄⁺) concentration and pH in the apoplast, the gaseous NH₃ concentration inside the leaves was calculated, i.e. the so-called stomatal compensation point (χ_s).Temperature appeared to have a predominant effect on χ_s, partly by affecting the equilibrium between gaseous NH₃ inside the leaf and NH₃ dissolved in the apoplast and partly by affecting physiological processes influencing the NH₄⁺ concentration in the apoplast. Results of the present study suggest that these temperature effects were counteracting. On one hand temperature increase during early spring stimulated NH₃ volatilisation from the apoplast, on the other hand it led to a decline in apoplastic NH₄⁺ from 0.9 to 0.2 mM, thereby diminishing the emission potential of the leaf. The low NH₄⁺ concentrations during spring and summer coincided with a low total leaf N content (<3% dw). However, there was no clear relationship between these two variables. The total N content of the leaf tissue is therefore an inadequate parameter for prediction of the potential NH₃ emission from rye grass leaves. No annual trend was found for the apoplast pH. With a few exceptions, pH varied between 5.9 and 6.5 throughout the experimental period.The calculated values for χ_s varied between 0.5 and 4 μg m⁻³. The gaseous NH₃ concentrations inside the grass leaves were, with a few exceptions, always smaller than the measured ambient NH₃ concentrations. The present study indicates that under the current ambient NH₃ concentrations in the Netherlands, the grass canopy is unlikely to be a major source of NH₃ emission.     

Evaluation of the RAMS Continuous Monitor for Determination of PM2.5 Mass Including Semi-Volatile Material in Philadelphia,PA

Abstract

The real-time ambient mass sampler (RAMS) is a continuous monitor based on particle concentrator, denuder, drier, and tapered element oscillating microbalance (TEOM) monitor technology. It is designed to measure PM_2.5 mass, including the semi-volatile species NH₄NO₃ and semi-volatile organic material, but not to measure PM_2.5 water content. The performance of the RAMS in an urban environment with high humidity was evaluated during the July 1999 NARSTO-Northeast Oxidant and Particles Study (NEOPS) intensive study at the Baxter water treatment plant in Philadelphia, PA. The results obtained with the RAMS were compared to mass measurements made with a TEOM monitor and to constructed mass obtained with a Particle Concentrator-Brigham Young University Organic Sampling System (PC-BOSS) sampler designed to determine the chemical composition of fine particles, including the semi-volatile species. An average of 28% of the fine particulate material present during the study was semi-volatile organic material lost from a filter during particle collection, and 1% was NH₄NO₃ that was also lost from the particles during sampling. The remaining mass was dominantly nonvolatile (NH₄)₂SO₄ (31%) and organic material (37%), with minor amounts of soot, crustal material, and nonvolatile NH₄NO₃. Comparison of the RAMS and PC-BOSS results indicated that the RAMS correctly monitored for fine particulate mass, including the semi-volatile material. In contrast, the heated filter of the TEOM monitor did not measure the semi-volatile material. The comparison of the RAMS and PC-BOSS data had a precision of ±4.1 μg/m³ (±9.6%). The precision of the RAMS data was limited by the uncertainty in the blank correction for the reversible adsorption of water by the charcoal-impregnated cellulose sorbent filter of the RAMS monitor. The precision of the measurement of fine par-ticulate components by the PC-BOSS was ±6-8%.     

Major ionic compositions of fine particulate matter in an animal feeding operation facility and its vicinity

Animal feeding operations (AFOs) produce particulate matter (PM) and gaseous pollutants. Investigation of the chemical composition of PM_2.5 inside and in the local vicinity of AFOs can help to understand the impact of the AFO emissions on ambient secondary PM formation. This study was conducted on a commercial egg production farm in North Carolina. Samples of PM_2.5 were collected from five stations, with one located in an egg production house and the other four located in the vicinity of the farm along four wind directions. The major ions of NH₄⁺, Na⁺, K⁺, SO₄^2?, Cl^?, and NO₃^? were analyzed using ion chromatography (IC). In the house, the mostly abundant ions were SO₄^2?, Cl^?, and K⁺. At ambient stations, SO₄^2?, and NH₄⁺ were the two most abundant ions. In the house, NH₄⁺, SO₄^2?, and NO₃^? accounted for only 10% of the PM_2.5 mass; at ambient locations, NH₄⁺, SO₄^2?, and NO₃^? accounted for 36–41% of the PM_2.5 mass. In the house, NH₄⁺ had small seasonal variations indicating that gas-phase NH₃ was not the only major force driving its gas–particle partitioning. At the ambient stations, NH₄⁺ had the highest concentrations in summer. In the house, K⁺, Na⁺, and Cl^? were highly correlated with each other. In ambient locations, SO₄^2? and NH₄⁺ had a strong correlation, whereas in the house, SO₄^2? and NH₄⁺ had a very weak correlation. Ambient temperature and solar radiation were positively correlated with NH₄⁺ and SO₄^2?. This study suggests that secondary PM formation inside the animal house was not an important source of PM_2.5. In the vicinity, NH₃ emissions had greater impact on PM_2.5 formation.

ImplicationsThe chemical composition of PM_2.5 inside and in the local vicinity of AFOs showed the impact of the AFO emissions on ambient secondary PM_2.5 formation, and the fate and transport of air pollutants associated with AFOs. The results may help to manage in-house animal facility air quality, and to develop regional air quality control strategies and policies, especially in animal agriculture-concentrated areas.     

Ammonia concentrations and modeling of inorganic particulate matter in the vicinity of an egg production facility in Southeastern USA

Ammonia (NH₃) is an important base gas and can react with acidic species to form atmospheric aerosols. Due to the rapid growth of poultry and swine production in the North Carolina Coastal Plain, atmospheric NH₃ concentrations across the region have subsequently increased. Ammonia concentrations and inorganic particulate matter (PM) at four ambient stations in the vicinity of an egg production facility were measured for 1 year using PM_2.5 speciation samplers with honeycomb denuders and ion chromatography (IC). Meanwhile, concentrations of NH₃ and inorganic PM in one of the egg production houses were also simultaneously measured using a gas analyzer for NH₃ and the filter pack plus IC method for inorganic PM. An equilibrium model-ISORROPIA II was applied to predict the behavior of inorganic aerosols in response to precursor gas concentrations and environmental parameters. Average ambient NH₃ concentrations varied from 10.0 to 27.0 μg/m³, and they were negatively correlated with the distances from the ambient location to the nearest egg production house exhausts. Ambient NH₃ concentrations were higher in warm seasons than in cold seasons. Measured NH₃ concentrations agreed well with ISORROPIA II model predictions at all sampling stations. For the ambient stations, there was a good agreement in particle phase NH₄ ⁺ between the model simulation and observations. For the in-house station, the model simulation was applied to correct the overestimation of particle phase NH₄ ⁺ due to gas phase NH₃ breaking through the denuders. Changes in SO₄ ^2?, NO₃ ^?, and Cl^? yield proportional changes in inorganic PM mass. Due to the abundance of NH₃ gas in the vicinity area of the monitored farm, changes in NH₃ concentrations had a small effect on inorganic PM mass. Aerosol equilibrium modeling may be used to assess the influence of precursor gas concentrations on inorganic PM formation when the measurements for some species are unavailable.     

Particulate contributions to light extinction and local forcing at a rural Illinois site

The light extinction and direct forcing properties of the atmospheric aerosol were investigated for a midwestern rural site (Bondville, IL) using field measurements, a semi-empirical light extinction model, and a radiative transfer code. Model inputs were based on the site measurements of the physical and chemical characteristics of atmospheric aerosol during the spring, summer, fall and winter of 1994. The light scattering and extinction coefficients were calculated and apportioned using the elastic light scattering interactive efficiency (ELSIE) model (Sloane and Wolff, 1985, Atmospheric Environment 19(4), 669–680). The average efficiencies calculated for organic carbon (OC, carbon measured as organic multiplied by 1.2) ranged from 3.81 m²/g OC at lower relative humidities (<63%) to 6.90 m²/g OC at higher relative humidities (>75%) while sulfate (assumed as ammonium sulfate) efficiencies ranged from 1.23 m²/g (NH₄)₂SO₄ to 5.78 m²/g (NH₄)₂SO₄ for the same range of relative humidities. Radiative transfer calculations showed that the rural aerosol at Bondville is most likely to have an overall negative (cooling) forcing effect on climate. Elemental carbon (EC), however, acts to counter sulfate forcing to a degree that has a significant seasonal variation, primarily due to the seasonal variation in the sulfate concentrations. Taking the loading to be the mean summer EC+ammonium sulfate loading and assuming [EC]/[(NH₄)₂SO₄] to be zero in one case (i.e. no soot present) and 0.025 (summer mean at Bondville) in another leads to a 37% difference in calculated forcing.     

Open-path,closed-path,and reconstructed aerosol extinction at a rural site

The Handix Scientific open-path cavity ringdown spectrometer (OPCRDS) was deployed during summer 2016 in Great Smoky Mountains National Park (GRSM). Extinction coefficients from the relatively new OPCRDS and from a more well-established extinction instrument agreed to within 7%. Aerosol hygroscopic growth (f(RH)) was calculated from the ratio of ambient extinction measured by the OPCRDS to dry extinction measured by a closed-path extinction monitor (Aerodyne’s cavity-attenuated phase shift particulate matter extinction monitor [CAPS PMex]). Derived hygroscopicity (relative humidity [RH] < 95%) from this campaign agreed with data from 1995 at the same site and time of year, which is noteworthy given the decreasing trend for organics and sulfate in the eastern United States. However, maximum f(RH) values in 1995 were less than half as large as those recorded in 2016—possibly due to nephelometer truncation losses in 1995. Two hygroscopicity parameterizations were investigated using high-time-resolution OPCRDS+CAPS PMex data, and the κ_ext model was more accurate than the gamma model. Data from the two ambient optical instruments, the OPCRDS and the open-path nephelometer, generally agreed; however, significant discrepancies between ambient scattering and extinction were observed, apparently driven by a combination of hygroscopic growth effects, which tend to increase nephelometer truncation losses and decrease sensitivity to the wavelength difference between the two instruments as a function of particle size. There was not a statistically significant difference in the mean reconstructed extinction values obtained from the original and the revised IMPROVE (Interagency Monitoring of Protected Visual Environments) equations. On average, IMPROVE reconstructed extinction was ~25% lower than extinction measured by the OPCRDS, which suggests that the IMPROVE equations and 24-hr aerosol data are moderately successful in estimating current haze levels at GRSM. However, this conclusion is limited by the coarse temporal resolution and the low dynamic range of the IMPROVE reconstructed extinction.

Implications: Although light extinction, which is directly related to visibility, is not directly measured in U.S. National Parks, existing IMPROVE protocols can be used to accurately infer visibility for average humidity conditions, but during the large fraction of the year when humidity is above or below average, accuracy is reduced substantially. Furthermore, nephelometers, which are used to assess the accuracy of IMPROVE visibility estimates, may themselves be biased low when humidity is very high. Despite reductions in organic and sulfate particles since the 1990s, hygroscopicity, particles’ affinity for water, appears unchanged, although this conclusion is weakened by the previously mentioned nephelometer limitations.     

A GC-TCD method for measuring the liquid water mass of collected aerosols

This work presents a gas chromatographic method that uses a thermal conductivity detector (GC-TCD) to measure the liquid water mass (LWM) of collected aerosols. The method is a modification of the previously developed EA-TCD method (Journal of Aerosol Science 29, 827). A microcomputer was incorporated into the system to control the analytical procedures, improve the measurement precision, and make possible a continuous operation. To validate the method, the aerosol LWMs of NaCl, Na₂SO₄, NH₄NO₃, (NH₄)₂SO₄, NH₄Cl, and Na₂CO₃ were measured at room temperature under relative humidities (RHs) varying between 20% and 90%, in both humidifying and dehumidifying conditions. Estimates of aerosol LWMs for varying aerosol chemical compositions and RHs by various measurement methods and predictive models are comprehensively compared. The comparison shows that the GC-TCD measurements agree closely with those of the other methods. The GC-TCD measurements are closer to the ISORROPIA model predictions than those of the AIM2 model. Most notably, our method determines, for the first time, the hygroscopic behavior of Na₂CO₃ aerosol yielding the deliquescence relative humidity and crystallization relative humidity at 78% and 39% RH, respectively. The hygroscopic characteristics of various NaCl mole fractions in mixed NaCl–Na₂SO₄ aerosols, determined by GC-TCD, are used to show the discrepancy between the measurements and the model's prediction.     

Difference in concentration trends of airborne particulate matter during rush hour on weekdays and Sundays in Tokyo,Japan

Suspended particulate matter (SPM) and fine particulate matter (less than or equal to 2.5 μm: PM_2.5) have generally been decreasing for the last decade in Tokyo, Japan. To elucidate the major cause of this decrease, the authors investigated the different trends of airborne particulates (both SPM and PM_2.5 concentrations) by evaluating comparisons based on the location of the monitoring stations (roadside vs. ambient), days of the week (weekdays vs. Sundays), and daily fluctuation patterns (2002 vs. 2010). Hourly mean SPM and PM_2.5 concentrations were obtained at four monitoring stations (two roadside stations, two ambient stations) in Tokyo, Japan. Annual mean concentrations of each day of the week and of each hour of the day from 2002 to 2010 were calculated. The results showed that (1) the daily differences in annual mean concentration decreased only at the two roadside monitoring stations; (2) the high hourly mean concentrations observed on weekdays during the daily rush hour at the two roadside monitoring stations observed in 2002 diminished in 2010; (3) the SPM concentration that decreased the most since 2002 was the PM_2.5 concentration; and (4) the fluctuation of hourly concentrations during weekdays at the two roadside monitoring stations decreased. A decreasing trend of airborne particulates during the daily rush hour in Tokyo, Japan, was observed at the roadside monitoring stations on weekdays since 2002. The decreasing PM_2.5 concentration resulted in this decreasing trend of airborne particulate concentrations during the daily rush hours on weekdays, which indicates fewer emissions were produced by diesel vehicles.

ImplicationsThe authors compared the trends of SPM and PM_2.5 in Tokyo by location (roadside vs. ambient), days of the week (weekdays vs. Sundays), and daily fluctuation patterns (2002 vs. 2010). The high hourly mean concentrations observed at the roadside location during rush hour on weekdays in 2002 diminished in 2010. The SPM concentration that decreased during rush hour the most was the PM_2.5 concentration. This significant decrease in the PM_2.5 concentration resulted in the general decreasing trend of SPM concentrations during the rush hours on weekdays, which indicates fewer emissions were produced from diesel vehicles.     

Determination of Source Contributions to Ambient PM2.5 in Kaohsiung,Taiwan, Using a Receptor Model

ABSTRACT

Ambient particulates of PM_2.5 were sampled at three sites in Kaohsiung, Taiwan, during February and March 1999. In addition, resuspended PM_2.5 collected from traffic tunnels, paved roads, fly ash of a municipal solid waste (MSW) incinerator, and seawater was obtained. All the samples were analyzed for twenty constituents, including water-soluble ions, organic carbon (OC), elemental carbon (EC), and metallic elements. In conjunction with local source profiles and the source profiles in the model library SPECIATE EPA, the receptor model based on chemical mass balance (CMB) was then applied to determine the source contributions to ambient PM_2.5.

The mean concentration of ambient PM_2.5 was 42.6953.68 μj.g/m³ for the sampling period. The abundant species in ambient PM_2.5 in the mass fraction for three sites were OC (12.7-14.2%), SO₄ ^2- (12.8-15.1%), NO₃ ^- (8.110.3%), NH₄+ (6.7-7.5%), and EC (5.3-8.5%). Results of CMB modeling show that major pollution sources for ambient PM_2.5 are traffic exhaust (18-54%), secondary aerosols (30-41% from SO₄ ^2- and NO₃ ^-), and outdoor burning of agriculture wastes (13-17%).     

The Denver Winter Aerosol: A Comprehensive Chemical Characterization

The sampling and chemical analysis of the ambient aerosol collected in Denver, CO, for a 40-day period during November and December, 1978 are described in this report. Parameters included 12-hr TSP measurements, 24-hr respirable and inhalable mass measurements, and 4-hr measurements of mass and chemical species (NO₃?, SO₄ =, NH₄ +, organic and elemental carbon as well as 13 chemical elements) in two size fractions i.e., less than 2.5 μm diameter (fine fraction) and larger than 2.5 μm diameter (coarse fraction). On the basis of the chemical analyses, it was possible to account for all particulate mass in both size fractions. In the fine fraction, the major constituents were organic carbon (21.6%), NH₄NO₃ (20.0%), elemental carbon (15.3%), (NH₄)₂SO₄ (13.6%), and the remainder consisted primarily of soil-like material, lead salts, and adsorbed water. Three quarters of the coarse fraction consisted of soil-like material, with the remainder composed of the same species that dominated the fine fraction.     

Seasonal variation of ionic species in fine particles at Qingdao,China

Totally nine measurement campaigns for ambient particles and SO₂ have been conducted during the period of 1997–2000 in Qingdao in order to understand the characteristics of the particulate matter in coastal areas of China. The mass fractions of PM_2.5, PM_2.5−10 and PM_>10 in TSP are 49%, 25% and 26%, respectively. The size distribution of particles mass concentrations in Qingdao shows bi-modal distribution. Mass fraction percentages of water-soluble ions in PM_2.5, PM_2.5−10 and PM_>10 decreased from 62% to 35% and 21%. In fine particles, sulfate, nitrate and ammonium, secondary formed compounds, are major components, totally accounting for 50% of PM_2.5 mass concentration.The ratios of sulfate, chloride, ammonium and potassium in PM_2.5 for heating versus non-heating periods are 1.34, 1.80, 1.56 and 1.44, respectively. The ratio of nitrate is 3.02 and this high ratio could be caused by reduced volatilization at lower temperature. Sulfate concentrations are higher than nitrate in PM_2.5. The chemical forms of sulfate and nitrate are probably (NH₄)₂SO₄ and NH₄NO₃ and chloride depletion was observed.Backward trajectory analysis reflected possible influence of air pollutant transport to Qingdao local aerosol pollution.     

A theoretical evaluation on the HNO3 artifact of the annular denuder system due to evaporation and diffusional deposition of NH4NO3-containing aerosols

A mathematical model was developed to evaluate HNO₃ artifact of the annular denuder system due to evaporation and diffusional deposition of nitrate-containing aerosols. The model performance was validated by comparing its numerical solutions with laboratory and numerical data available in the literature for evaporation and diffusional deposition of monodisperse and polydisperse NH₄NO₃ aerosols. Measurement artifacts were evaluated by varying typical sampling ranges of ambient temperature, HNO₃ gas concentration, aerosol number concentration, aerosol mass median diameter, and nitrate mass fraction of <2.5 μm aerosols to see their respective effects. Potential application of the present model on estimating HNO₃ artifacts was demonstrated using literature data sampled in USA, Taiwan, Netherlands, Korea and Japan. Significant measurement artifact could be found in Taiwan and Netherlands due either to low HNO₃ gas concentration and high nitrate concentration in <2.5 μm aerosols or to high ambient temperature.     

The Recovery of Ammonia and Hydrogen Sulflde from Ground-Level Area Sources Using Dynamic Isolation Flux Chambers: Bench-Scale Studies

Abstract

Controlled bench-scale laboratory experiments were conducted to evaluate the recovery of ammonia (NH₃) and hydrogen sulflde (H₂S) from dynamic isolation flux chambers. H₂S (80–4000 ppb) and NH₃ (5000–40,000 ppb) samples were diffused through the flux chamber to simulate ground level area source emissions while measuring the inlet and outlet flux chamber concentrations simultaneously. Results showed that the recovery of H₂S during a 30-min sampling time was almost complete for concentrations >2000 ppb. At the lowest concentration of 80 ppb, 92.55% of the H₂S could be recovered during the given sampling period. NH₃ emissions exhibited similar behavior between concentrations of 5000–40,000 ppb. Within the 30-min sampling period, 92.62% of the 5000-ppb NH₃ sample could be recovered. Complete recovery was achieved for concentrations >40,000 ppb. Predictive equations were developed for gas adsorption. From these equations, the maximum difference between chamber inlet and outlet concentrations of NH₃ or H₂S was predicted to be 7.5% at the lowest concentration used for either gas. In the calculation of emission factors for NH₃ and H₂S, no adsorption correction factor is recommended for concentrations >37,500 ppb and 2100 ppb for NH₃ and H₂S, respectively. The reported differences in outlet and inlet concentration above these ranges are outside the full-scale sensitivity of the gas sensing equipment. The use of 46–90 m of Teflon tubing with the flux chambers has apparently no effect on gas adsorption, because recovery was completed almost instantaneously at the beginning of the tests.     

Optical properties of the San Joaquin Valley aerosol collected during the 1995 integrated monitoring study

Optical, filter chemistry, and cascade impactor data collected during the winter intensive of the IMS95 Study in the San Joaquin Valley (SJV) of California were analyzed to determine the light-extinction efficiency of aerosol species. Regression of light scattering by particles (b_sp) measured by a heated nephelometer without a size selective inlet against PM_2.5 front filter mass gave a scattering efficiency of 3.67±0.05 m²/g with an R² (fraction of variance explained) of 0.94. Division of the aerosol into two components and applying two different corrections to the filter data for nitrate and organic carbon on the backup filter gave scattering efficiencies of 3.7±0.3 or 4.1±0.2 m²/g for the salts composed of sulfate, nitrate, and ammonium and 2.9±0.2 or 3.1±0.2 m²/g for all other species with R² of 0.985 and 0.986. The ambient b_sp measured by an open nephelometer was a simple function of PM_2.5 mass and relative humidity (RH), giving R² of 0.90 and 0.88 for two different RH sensors. Variations in PM_2.5 size distribution and composition did not have an important effect on ambient b_sp. The RH data from each sensor were repeatable enough to show the existence of a simple dependence of aerosol water uptake on RH, but RH sensor calibration uncertainties prevented determining this dependence. Inversion of MOUDI cascade impactor data gave sulfate and nitrate mass median diameters (MMD) between 0.4 and 0.8 μm. Mie scattering calculations based on MOUDI data provided humidity-dependent extinction efficiencies for the principal aerosol chemical species. These efficiencies combined with particle filter data showed that ammonium nitrate was the dominant contributor to wintertime light extinction. Source apportionment showed that light extinction was dominated by emissions sources contributing to the formation of secondary species, especially nitrate. These wintertime data are not expected to apply to summertime in the SJV.     

An examination of the physical and optical properties of aerosols collected in the IMPROVE program

The Interagency Monitoring of Protected Visual Environments (IMPROVE) protocols for reconstructing the ambient light extinction coefficient (b_ext) from measured aerosol species are the basis for evaluating compliance under the Regional Haze Rule. Aerosol mass composition and optical properties have been measured as part of the IMPROVE program since 1988, providing a long-term data set of aerosol properties at 38 sites around the US. This data set is used to evaluate assumptions made in calculating reconstructed mass and b_ext by applying statistical analysis techniques. In particular, the molecular weight to carbon weight ratio used to compute particulate organic matter is investigated. An annual average value of 1.7±0.2 for the IMPROVE sites, compared to the value of 1.4 currently assumed in the IMPROVE algorithm, is derived. Regression analysis also indicates that fine soil mass concentrations are underestimated by roughly 20% on average. Finally, aerosol mass scattering and extinction efficiencies assumed in the IMPROVE reconstructed b_ext protocol are examined. Fine mode (D_p<2.5 μm) mass scattering efficiencies have a functional dependence on mass concentrations at many sites, and use of a mass-concentration-dependent adjustment factor to refine the assumed efficiencies provides for closer agreement between measured and reconstructed b_ext.     

An evaluation of artifact SO42− formation on nylon filters under field conditions

The extent of SO₂ conversion on Membrana (Ghia) Nylasorb nylon filters under field conditions has been evaluated and found to be quite variable. The S-SO₄²⁻ loading on the nylon filters is higher at higher SO₂ concentrations, and on a long term basis approaches a saturatio limit of 2.5 μg S-SO₄²⁻ on a 47mm disc, at a dosage of 230 μg SO₂ approximately. The % conversion decreases as the SO₂ concentration increases. On a long term basis, at an SO₂ concentration range of 1.0–7.7 μg m⁻³, the conversion ranges from 8.2% to 2.1%. The dependence of SO₂ conversion on nylon filters on relative humidity displays a diurnal pattern. An expression has been derived to explain the observed % SO₂ conversion on nylon filters as a combined effect of the ambient SO₂ concentration and relative humidity.     

Vertical distribution of gases and aerosols: The behaviour of ammonia and related components in the lower atmosphere

Vertical concentration profiles for NH₃, HNO₃ and HCl-gas and for NH₄⁺, NO₃⁻, SO²⁻₄, Cl⁻ and Na⁺ aerosol were obtained from a meteorological tower in the central part of the Netherlands. An upward NH₃ flux of 0.12 μgm⁻² s⁻¹ was calculated from the NH₃ profiles and meteorological data. From the HNO₃ profiles a maximum HNO₃ dry deposition velocity of 4 cm s⁻¹ was calculated. Good agreement was found between the measured concentration products [NH₃]_(g) × [HNO₃]_(g) and the theoretical values at temperatures above 0°C and relative humidities below 80%. In other cases, higher NH₃ and/or HNO concentrations in the gas phase were measured than theoretically predicted.     

用微电极测定曝气量对SBR系统中硝化作用的影响

为了研究曝气量对硝化作用的影响,实验采用3个相同的SBR装置,分别在曝气量为4、10和16 L/h的条件下处理人工污水,并采用自制的溶解氧、NO3-、NH4+和pH微电极测定了活性污泥絮体内部微元环境中相应基质的浓度。结果表明,曝气量为4 L/h时,活性污泥絮体内存在厌氧微区,NO3--N浓度减小了,发生了反硝化作用;而曝气量为10 L/h和16 L/h时,活性污泥絮体内发生的都是硝化反应,且NH4+-N浓度的减小量、NO3--N浓度的增大量都随着曝气量的增大而增大,pH随着曝气量的增大而减小。     

Measurements of Pollutants inside an Automobile

A series of experiments was conducted to determine the concentration of certain pollutants inside a car under typical driving conditions. The work was performed during the summer months in the Los Angeles area and measurements of O₃, CO, NO, and NO_x were taken. It was found that the O₃ concentration in the passenger compartment may be maintained at relatively low values provided that the influx of outside air is limited. The low levels were explained by decay of O₃ on surfaces within the compartment. The average concentration of the other components inside the car is about equal to that on the outside. In the current tests, however, the measured concentrations did not exceed any of the present standards.     

低温等离子体氧化氨气影响因素及动力学研究

采用电晕放电低温等离子体处理模拟氨气恶臭气体,考察了输入功率、初始浓度、气体湿度、停留时间等因素对降解效果和能量效率的影响,同时对反应过程进行了动力学研究。研究表明,输入功率以及停留时间对氨气降解的影响是积极的,但能量效率随着两者的增加先增大后减小。氨气的降解率随着初始浓度的增加而降低,而能量效率随着输入功率的增加而增加。氨气降解率和能量效率均随着气体湿度的增加而增加,当气体湿度为45%时达到最大值,然而随着气体湿度的进一步增加,其降解率和能量效率反而降低。反应尾气中臭氧浓度随着输入功率的增加而不断升高,而氨气的存在却使臭氧浓度有不同程度的降低。对电晕放电低温等离子体处理NH3的反应动力学进行了分析,得到NH3的反应速率常数为kNH3=0.0707 m3/(W·h)。