Concentrations Of Gaseous NH3 Research Articles

Simple Framework to Quantify the Contributions from Different Factors Influencing Aerosol pH Based on NHx Phase-Partitioning Equilibrium.

While aerosol pH is among the most important parameters in atmospheric chemistry, it can be challenging to have a priori knowledge of the factors that are most strongly influencing the pH in a specific environment. In this study, we present a calculation method to more intuitively quantify the relationship between aerosol pH and its influencing factors, including gaseous NH3 concentration, particle properties, relative humidity, temperature, and nonvolatile cations, based on the NHx phase-partitioning equilibrium used in the E-AIM thermodynamic model. The applications of this calculation framework include (1) expressing the pH values directly as the function of influencing factors, (2) quantitatively studying the contribution of different factors to pH value changes, and (3) decomposing the standard deviation of pH values to find the dominant influencing factors on total pH fluctuations. This calculation framework provides a direct, quantitative, and intuitive approach to interpret pH values and differences. The relationship derived from pH and phase partitioning of semivolatile NHx can be extended to other phase-partitioning pairs as well. Our method provides a new way to quantitatively study pH and allows the pH studies conducted in different locations and meteorological conditions to be more easily compared and interpreted.

New insights into the N2O formation mechanism during selective catalytic reduction of NO with NH3 over V-based catalyst

Abstract Formation of N2O during NH3-SCR reaction limits the temperature window of SCR catalyst. In the present study, a series of kinetics experiments were carried out over V-based catalyst to study the N2O formation characteristics at different temperatures. Transient and temperature-programmed reactions show that the thermal decomposition of solid NH4NO3 formed by the reaction of NH3 with NO2 is the main way of N2O formation at low temperatures (below 300 °C). At the temperature above 300 °C, N2 selectivity of NO reduction over V-based catalysts decreases with the increase of the gaseous NH3 concentration and the V content of the catalysts. DFT calculations were applied to understand the formation mechanism of N2O at high temperature. The results show that the NH is found to be formed by NH3 oxidative dehydrogenation over V Lewis acid site and subsequently reacts with NO to produce N2O. In this process, the deep oxidation of the adsorbed NH3 is the rate-determined step, which can be aggravated by the high temperature and high V content.

Performance of CO2 absorption in a spray tower using blended ammonia and piperazine solution: Experimental studies and comparisons

Slow CO2 absorption rate is one of the major drawbacks of the ammonia-based CO2 capture. To overcome the drawback, piperazine (PZ) is widely recommended to add into the aqueous NH3 solution as a promoter. In this work, we experimentally studied the performance of CO2 absorption in a spray tower using the blended NH3/PZ solution. The effects of varying operating parameters on the CO2 removal efficiency, outlet gaseous NH3 concentration, ammonia loss mass ratio, and volumetric overall mass transfer coefficients Kg,CO2aV have been revealed. Considering that the volumetric overall mass transfer coefficient Kg,CO2aV is an important parameter for CO2 capture application, we further shed some light on the underlying relationships between the coefficients Kg,CO2aV and the operating parameters. Additionally, to examine the feasibility of the blended solution in a spray tower, we compared the absorption characteristics identified in this work with those reported in the literature using NH3 or the blended NH3/PZ solution as absorbents. The comparisons demonstrate CO2 absorption in a spray tower using the blended NH3/PZ solution can be a great potential alternative for the CO2 capture and storage technologies.

Reactive uptake of ammonia by secondary organic aerosols: Implications for air quality

Reactions between ammonia (NH3) and organic compounds containing carbonyl functional groups in aerosol particles can form organic products that are less basic than NH3 and are thus unable to neutralize efficiently nitric and sulfuric acids. In this exploratory study, the University of California, Irvine - California Institute of Technology (UCI-CIT) model is used to investigate the potential air quality impacts of including of the chemical uptake of NH3 by secondary organic aerosols (SOA) in a regional airshed model. A surface reaction of NH3 with SOA is implemented into the model to determine the impact of this process on NH3 and PM2.5 concentrations in the South Coast Air Basin of California (SoCAB). Air quality simulations are conducted using uptake coefficients ranging from 10−5 to 10−2 to explore the sensitivity of changes in NH3 and PM2.5 concentrations to the magnitude of the uptake coefficient. Results indicate that the chemical uptake of NH3 by SOA can potentially deplete gaseous NH3 concentrations, causing indirect reductions in the amount of ammonium nitrate and ammonium sulfate in particulate matter. The magnitude of the impact on NH3 and PM2.5 concentrations exhibits a strong but non-linear dependence on the value of the uptake coefficient, with evidence for small but notable impacts on air quality even with the lowest assumed uptake coefficient of 10−5.

Room temperature amine sensors enabled by sidewall functionalization of single-walled carbon nanotubes.

A new series of sidewall modified single-walled carbon nanotubes (SWCNTs) with perfluorophenyl molecules bearing carboxylic acid or methyl ester moieties are herein reported. Pristine and functionalized SWCNTs (p-SWCNTs and f-SWCNTs, respectively) were characterized by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and scanning electron microscopy (SEM). The nitrene-based functionalization provided intact SWCNTs with methyl 4-azido-2,3,5,6-tetrafluorobenzoate (SWCNT-N-C6F4CO2CH3) and 4-azido-2,3,5,6-tetrafluorobenzoic acid (SWCNT-N-C6F4CO2H) attached every 213 and 109 carbon atoms, respectively. Notably, SWCNT-N-C6F4CO2H was sensitive in terms of the percentage of conductance variation from 5 to 40 ppm of ammonia (NH3) and trimethylamine (TMA) with a two-fold higher variation of conductance compared to p-SWCNTs at 40 ppm. The sensors are highly sensitive to NH3 and TMA as they showed very low responses (0.1%) toward 200 ppm of volatile organic compounds (VOCs) containing various functional groups representative of different classes of analytes such as benzene, tetrahydrofurane (THF), hexane, ethyl acetate (AcOEt), ethanol, acetonitrile (CH3CN), acetone and chloroform (CHCl3). Our system is a promising candidate for the realization of single-use chemiresistive sensors for the detection of threshold crossing by low concentrations of gaseous NH3 and TMA at room temperature.

Dry and Bulk Nitrogen Deposition in Suburbs of Xining City

This study conducted a full two-year (2014 and 2015) measurements of dry and bulk deposition of atmospheric inorganic nitrogen (N) at the suburb of Xining city, Qinghai province. Dry N deposition fluxes were calculated by multiplying the atmospheric concentrations of NH3 and NO2 measured using passive samplers with the modeled dry deposition velocities provided by the GEOS-Chem global chemical transport model, while bulk N deposition fluxes were measured using precipitation gauge. Annual mean concentrations of gaseous NH3 and NO2 averaged 8.8 and 19.6 μg·m-3, respectively, with significantly higher values in 2015 than in 2014. Seasonal mean NH3 concentrations were higher in spring and summer than in autumn and winter, but the concentrations of NO2 changed little from season to season, with a small peak in autumn. Annual mean concentrations of NH4+-N and NO3--N in precipitation averaged 2.2 and 1.8 mg·L-1, respectively. Concentrations of NH4+-N in autumn were~55% lower than those in other seasons, whereas those of NO3--N in autumn or winter were~26% higher than those in spring and summer. Dry deposition of NH3 and NO2 was 9.0 and 2.8 kg·(hm2·a)-1, respectively. Bulk deposition of NH4+-N and NO3--N in precipitation was 7.6 and 6.2 kg·(hm2·a)-1, respectively. Reduced N (gaseous NH3 and NH4+-N in precipitation) was the dominant form of N deposition. The total dry and wet N deposition was 25.6 kg·(hm2·a)-1, which represented significant nutrient input from the environment to the suburban farmland, but this amount of deposited N exceeded the critical loads[10-20 kg·(hm2·a)-1] of terrestrial ecosystems, suggesting a risk of "N saturation" in the local natural environment.

Quantification of nitrogen dry and wet deposition in Fujian tobacco planting area

In this study, the wet/bulk and dry atmospheric deposition of different inorganic nitrogen (N) species was investigated in the Fujian tobacco planting area from 2010 to 2014. Wet/bulk N deposition flux of inorganic N was monitored at five sites (Fuzhou, Shanghang, Changting, Taining, and Wuyishan) of Fujian by using precipitation gauges. While dry deposition fluxes of gaseous NH3, NO2, and HNO3 (gNH3, gNO2, and gHNO3), and particulate NH4+ and NO3− (pNH4+ and pNO3−) were estimated only at the Fuzhou site through multiplying monthly mean Nr concentrations obtained from DELTA (DEnuder for Long-Term Atmospheric sampling) system (gNH3, gHNO3, pNH4+, pNO3−) and passive samplers (gNO2) and the modeled monthly mean dry deposition velocities provided by the GEOS-Chem global chemical transport model. Annual mean NH4+-N, NO3−-N, and total inorganic N (TIN) concentrations in precipitation (rainwater and snow) were 0.21–1.05, 0.33–0.74, and 0.59–1.68mgNL−1, respectively, and the averages over the monitoring period were 0.55, 0.49, and 1.04mgNL−1, respectively. Across the five monitoring sites, the average annual wet/bulk N deposition was 17.6kgNha−1a−1, while that of NH4+-N and NO3−-N amounted to 9.2 and 8.4kgNha−1a−1, respectively. Wet/bulk deposition was lowest at Changting, but no significant differences were found between the other four sites. Annual mean atmospheric concentrations of gNH3, gNO2, gHNO3, pNH4+, and pNO3− were 1.87, 2.95, 0.45, 2.36, and 1.23μgNm−3, respectively. Gaseous NH3 concentrations were highest in summer and lowest in winter. In contrast, seasonal fluctuations in other measured Nr species (e.g., gNO2) were not as large as those of gNH3.The annual mean total dry deposition was estimated to be 9.6kgNha−1a−1, and those of the individual species, gNH3, gNO2, gHNO3, pNH4+, and pNO3− were estimated to be 4.1, 2.2, 2.0, 0.8, and 0.4kgNha−1a−1, respectively. Based on the similarities in wet deposition, if we assume a similar level of dry deposition at all the sites, the total (dry and wet) N deposition was 27.2kgNha−1a−1 on average, which twice the critical load (10–15kgNha−1a−1) for forest ecosystems, suggesting a risk of “N saturation” in the local natural environment.

Impact of the oasis effect on wind tunnel measurements of ammonia volatilization from urea

The validity of emission factors derived from small-scale measurements of ammonia (NH3) volatilization has been questioned in the literature because gaseous NH3 concentration gradients differ at the edge of the measurement plot and may result in higher emissions than at field scale. We studied this “oasis effect” using two very long (22 m) wind tunnels constructed indoors over soil plots fertilized with surface-applied urea (20 g N m−2). We hypothesized that NH3 flux would be highest at the start of the tunnel and decrease with distance. Air NH3 concentration was measured every 2 m along each tunnel for 2 wk after urea application; NH3 flux did not decrease along the length of the tunnels. Of the 60 measurement periods, when there was significant NH3 volatilization, only two had a significant nonlinear relationship (P ≤ 0.05) between NH3 concentration and distance. For the other periods, the NH3 concentration increased linearly with distance (P ≤ 0.05). The background NH3 concentration difference between halves of the tunnels was not significantly related to NH3 flux difference (P > 0.1). Our results indicate that wind tunnel measurements of NH3 volatilization fertilized using urea are not impacted by a measurable oasis effect.

N2 Selectivity of NO Reduction by NH3 over MnOx–CeO2: Mechanism and Key Factors

In this work, the novel relationships of N2 selectivity of NO reduction over MnOx–CeO2 with the gas hourly space velocity (i.e., GHSV) and the reactants’ concentrations were discovered. Meanwhile, the mechanism of N2O formation during the low temperature selective catalytic reduction reaction (SCR) over MnOx–CeO2 was studied using in situ DRIFTS study and the transient reaction study. N2O formation over MnOx–CeO2 mainly resulted from the Eley–Rideal mechanism (i.e., the reaction between overactivated NH3 and gaseous NO), and the Langmuir–Hinshelwood mechanism (i.e., the reaction between adsorbed NH3 species and adsorbed NOx) did not contribute to N2O formation. There was an excellent linear relationship of NO reduction and N2 formation with gaseous NO concentration. Meanwhile, the reaction order of N2O formation with respect to gaseous NO concentration was nearly 1. However, the reaction orders of NO reduction, N2O formation, and N2 formation over MnOx–CeO2 with respect to gaseous NH3 concentration were a...

Mechanism of N2O formation during the low-temperature selective catalytic reduction of NO with NH3 over Mn-Fe spinel.

The mechanism of N2O formation during the low-temperature selective catalytic reduction reaction (SCR) over Mn-Fe spinel was studied. The in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and transient reaction studies demonstrated that the Eley-Rideal mechanism (i.e., the reaction of adsorbed NH3 species with gaseous NO) and the Langmuir-Hinshelwood mechanism (i.e., the reaction of adsorbed NH3 species with adsorbed NOx species) both contributed to N2O formation. However, N2O selectivity of NO reduction over Mn-Fe spinel through the Langmuir-Hinshelwood mechanism was much less than that through the Eley-Rideal mechanism. The ratio of NO reduction over Mn-Fe spinel through the Langmuir-Hinshelwood mechanism remarkably increased; therefore, N2O selectivity of NO reduction over Mn-Fe spinel decreased with the decrease of the gas hourly space velocity (GHSV). As the gaseous NH3 concentration increased, N2O selectivity of NO reduction over Mn-Fe spinel increased because of the promotion of NO reduction through the Eley-Rideal mechanism. Meanwhile, N2O selectivity of NO reduction over Mn-Fe spinel decreased with the increase of the gaseous NO concentration because the formation of NH on Mn-Fe spinel was restrained. Therefore, N2O selectivity of NO reduction over Mn-Fe spinel was related to the GHSV and concentrations of reactants.

Abundance and distribution of gaseous ammonia and particulate ammonium at Delhi, India

Abstract. This study reports abundance and distribution of gaseous NH3 and particulate NH4+ at Delhi. Gaseous NH3 and particulate NH4+ concentrations were measured during pre-monsoon, monsoon and post-monsoon seasons of the years 2010 and 2011. Average concentrations of gaseous NH3 during pre-monsoon, monsoon and post-monsoon seasons were recorded as 26.4, 33.2 and 32.5 μg m−3, respectively. Gaseous NH3 concentrations were the highest during monsoon, thought to be due to decay and decomposition of plants and other biogenic material under wet conditions, leading to increased NH3 emission. The results showed that particulate NH4+ was always lower than the gaseous NH3 during all the seasons. The concentrations of particulate NH4+ were recorded as 11.6, 22.9 and 8.5 μg m−3 during pre-monsoon, monsoon and post-monsoon seasons, respectively. The percent fraction of particulate NH4+ was noticed to be highest during the monsoon season, which is attributed to increased humidity levels favouring partitioning into the aerosol phase. On an average, 33.3% of total N-NHx was present as particulate NH4+. Higher concentrations of NH3 noticed during night time may be due to stable atmospheric conditions. The study highlighted that, as compared with rural sites, urban sites showed higher concentrations of gaseous NH3 in India, which may be due to higher population density, human activities and poor sanitation arrangements.

Uncertainty Modelling to Evaluate Nitrogen Balances As a Tool to Determine N2 and N2O Formation in Ammonia Bioscrubbers

Biological scrubbers aim at reducing gaseous ammonia emissions by transferring it to a water phase followed by conversion to nitrite and nitrate. A small part of the removed nitrogen may be emitted as N2 and N2O produced as a result of denitrification processes. Due to the large greenhouse warming potential of N2O, even a small emission could be a point of concern. Determining these N losses in form of N2 and N2O via nitrogen balance is an alternative, but little is known about the uncertainty associated to this method. The main aim of this work was to develop an uncertainty model that evaluated N-balances in biological scrubbers in terms of result uncertainty. Secondary objectives were to provide a methodology to determine individual uncertainties involved, and to conduct a sensitivity analysis to identify the main contributors to the final uncertainty. For a defined scenario (biotrickling scrubber, 70% NH3 removal; 5% of inlet N-NH3 lost as N2 and N2O), the standard uncertainty expressed in relative terms of the average was 132% (released N in form of N2 and N2O). Main contributors to the final uncertainty were airflow rate and water volume in the scrubber basin. Uncertainty of the measurements of gaseous NH3 concentrations and N compounds in water had a reduced effect on the final uncertainty. Based on these results, N balances are not recommended to evaluate N2 and N2O formation in biological scrubbers, at least for the conditions considered in this work.

Dry deposition of reactive nitrogen to European ecosystems: a comparison of inferential models across the NitroEurope network

Abstract. Inferential models have long been used to determine pollutant dry deposition to ecosystems from measurements of air concentrations and as part of national and regional atmospheric chemistry and transport models, and yet models still suffer very large uncertainties. An inferential network of 55 sites throughout Europe for atmospheric reactive nitrogen (Nr) was established in 2007, providing ambient concentrations of gaseous NH3, NO2, HNO3 and HONO and aerosol NH4+ and NO3− as part of the NitroEurope Integrated Project. Network results providing modelled inorganic Nr dry deposition to the 55 monitoring sites are presented, using four existing dry deposition routines, revealing inter-model differences and providing ensemble average deposition estimates. Dry deposition is generally largest over forests in regions with large ambient NH3 concentrations, exceeding 30–40 kg N ha−1 yr−1 over parts of the Netherlands and Belgium, while some remote forests in Scandinavia receive less than 2 kg N ha−1 yr−1. Turbulent Nr deposition to short vegetation ecosystems is generally smaller than to forests due to reduced turbulent exchange, but also because NH3 inputs to fertilised, agricultural systems are limited by the presence of a substantial NH3 source in the vegetation, leading to periods of emission as well as deposition. Differences between models reach a factor 2–3 and are often greater than differences between monitoring sites. For soluble Nr gases such as NH3 and HNO3, the non-stomatal pathways are responsible for most of the annual uptake over many surfaces, especially the non-agricultural land uses, but parameterisations of the sink strength vary considerably among models. For aerosol NH4+ and NO3− discrepancies between theoretical models and field flux measurements lead to much uncertainty in dry deposition rates for fine particles (0.1–0.5 μm). The validation of inferential models at the ecosystem scale is best achieved by comparison with direct long-term micrometeorological Nr flux measurements, but too few such datasets are available, especially for HNO3 and aerosol NH4+ and NO3−.

Comparison of Ammonium Deposition Flux at Roadside and at an Agricultural Area for Long-Term Monitoring: Emission of Ammonia from Vehicles

To understand the effect of the NH3 emissions from vehicles, the NH4+ bulk deposition and concentrations of gaseous NH3 and particulate NH4+ were measured at two sites in Saitama prefecture, Japan, one at the roadside of an arterial road (Kounosu), and the other in an agricultural area (Kisai). We observed that the NH4+ bulk deposition and NH3 concentration were significantly increased in Kounosu; the effect of NH3 emissions from vehicles was confirmed. NOx was a primary pollutant mainly emitted by vehicle exhaust in the vicinity of arterial roads, and the relationship between NOx and sum of gaseous NH3 and particulate NH4+ (T-NH4+) was examined. The [T-NH4+/NOx] ratios in Kounosu ranged from 0.08 to 0.23 (average 0.15), and in Kisai they ranged from 0.16 to 0.67 (average 0.39). In Kounosu, the effect of vehicle exhaust was great, but seasonal variation was small. The contribution ratio of NH3 from vehicle emissions increased at low temperatures, while that from the non-vehicle emissions increased at high temperatures.

Atmospheric phase distribution of oxidized and reduced nitrogen at a forest ecosystem research site

Atmospheric concentrations of gaseous NH3 and HNO3 and of particulate NH4+ and NO3- were measured during various seasons at a forest ecosystem research site in the "Fichtelgebirge" mountains in Central Europe. Air masses arriving at this site were highly variable with respect to trace compound concentration levels and their concentration ratios. However, the distributions of NH4+ and NO3- within the aerosol particle size spectra exhibited some very consistent patterns, with the former dominating the fine particle concentrations, and the latter dominating the coarse particles range, respectively. Overall, the particulate phase (NH4+ + NO3-) dominated the atmospheric nitrogen budget (particulate and gas phase, NH4+ + NO3- + NH3 + HNO3) by more than 90% of the median total mixing ratio in winter, and by more than 60% in summer. The phase partitioning varied significantly between the winter and summer seasons, with higher relative importance of the gaseous species during summer, when air temperatures were higher and relative humidities lower as compared to the winter season. Reduced nitrogen dominated over oxidized nitrogen, indicating the prevailing influence of emissions from agricultural activity as compared to traffic emissions at this mountainous site. A model has been successfully applied in order to test the hypothesis of thermodynamic equilibrium between the particulate and gas phases.

Modeling study of cloud droplet nucleation and in‐cloud sulfate production during the Sanitation of the Atmosphere (SANA) 2 campaign

Based upon the measurements of vertical profiles of gaseous SO2, H2O2, O3, and meteorological parameters from aircraft and of the aerosol chemical composition and gaseous NH3, HNO3, and SO2 at the surface in southeastern Germany (Melpitz) during the Sanitation of the Atmosphere (SANA) 2 campaign, realistic modeling of cloud droplet nucleation and in‐cloud sulfate production was performed with an explicit microphysical cloud model with size‐resolved chemistry and cloud top entrainment. For the fair weather cumulus observed during the measurements, the calculated cloud droplet number concentrations could be as high as 2000 cm−3 (and precloud aerosol sulfate up to 9.1 μg m−3), indicating strong sulfur pollution at Melpitz during the campaign. The in‐cloud sulfate production is within 1.5–5.0 μg m−3, depending on the initial gaseous NH3 concentration in the parcel. This result shows the necessity of gaseous NH3 vertical profile measurements. Entrainment can reduce the cloud droplet number concentration and cause the distribution of in‐cloud produced sulfate to shift toward larger particle sizes. Under the cases we studied, we do not find a significant effect of cloud top gaseous H2O2 entrainment on the in‐cloud sulfate production. For the adiabatic cases the departure of bulk water H2O2 from the Henry's law equilibrium is very small. When entrainment included, however, bulk water H2O2 concentrations could be clearly less than the equilibrium values, and the deficiencies are higher (>20%) for droplets larger than 10 μm radius. Our results suggest that entrainment could be one of the important factors to account for the measured H2O2 deficiency in cloud water.