Communication—Partial Oxidation of MnS for Synergistic Electrocatalysis of N2-to-NH3 Fixation at Ambient Conditions

Compared with the traditional Haber-Bosch process, electrochemical N2-to-NH3 reduction affords an eco-friendly and sustainable alternative to ambient NH3 synthesis with the aid of efficient electrocatalysts. In this work, partial oxidation of MnS to obtain the MnS-Mn3O4 is proved as a promising noble-free electrocatalysts of N2to NH3 fixation at ambient conditions. When tested in 0.1 M Na2SO4, the electrochemical N2 reduction reaction performance of MnS-Mn3O4 is improved comparing with the MnS, which achieves large NH3 yield of 16.74 μg h–1 mgcat.–1 and a high Faradaic efficiency of 5.72%. It also exhibits excellent selectivity of N2-to-NH3 and strong long-term electrochemical stabil

Diurnal Variation of Ambient NH3 in Relation with Agricultural Activities and Meteorological Factors at a Rural Site in North India

Ammonia is a chemically active gas which accelerates particulate matter formation by combining with nitrate (NO3−) and sulphate (SO42-) in acid cloud droplets, thereby reducing air quality. Since pre-industrial times, NH3 emissions have more than doubled globally, owing to increase in agricultural activities and fertilizer usage. In this study, ambient NH3 monitoring was done during selected periods on event basis in summer season (kharif crop) at a rural site of Jhajjar district of Haryana. Collected gaseous NH3 samples in absorbing solution (1.4ml H2SO4 in 1 litre water) at a flow rate of 1 LPM were prepared with the indo phenol-blue method and analyzed using spectrophotometer at 630nm. Here, we present the day-night variation in ambient NH3 concentrations emitted from various agricultural activities such as synthetic fertilizers, animal manure, biological N-fixation, the crop residue in the field after harvest, biomass burning, etcin relation with meteorological parameters. Its emission was recorded as 1 to 45; 63 to 190; 98 to 187 and 56 to 249 µg m-3 during sowing, fertilizer addition, grain filling and biomass burning respectively.Concentration during the sowing period i.e. 1 to 45 µg m-3can be considered as baseline values.Concentration of ambient NH3 reached itsmaxima at night and minima duringmidday.NH3 concentration was observed to be high during night time which might be due to reduced dispersion as the atmospheric conditions are stable at night. Concentration of NH3 is majorly influenced by wind speed and wind direction & its dependence on these meteorological parameters suggested a local source influence indicating that the nearbyagricultural fields might be the major NH3contributors at the observational site.This study suggests that the knowledge of NH3 levels measured at various stages can help in implementing N efficient management system and emissions can be reduced by minimizing the Nitrogen (N) input during different stages. These measurements are also helpful in making fertilizer policy, and guidelines for farmers.

PM2.5 acidity during haze episodes in Shanghai, China

Environmental contextAerosol acidity, or aerosol aqueous phase pH, can affect various environmental processes. Based on high frequency measurements of particulate compositions, along with thermodynamic calculations, this work studies particle acidity in the course of severe episodes of haze in Shanghai and considers the effect of this on the production of nitrate. The results will provide new perspectives on our interpretation of PM2.5 acidity during haze episodes in megacities. AbstractAerosol acidity is one of the most important parameters that can influence climate change and human health, which has been inadequately analysed in China. Here, hourly measurements of particulate compositions and the E-AIM II model (assuming thermodynamic equilibrium) were used to study particle acidity during severe episodes of haze in Shanghai. The total concentration of sulfate, nitrate and ammonium was 138.9 ± 50.6 μg m−3, maximum 241.3 μg m−3; and the PM2.5 to PM10 (PM2.5/PM10) ratio was 0.60. The fine particles detected were somewhat acidic, with a pH range of 0.04–4.50, average 2.34, which is higher than in some areas of the US and China. The relatively low particle acidity is attributed to particle water content levels. Furthermore, the growth rate of sulfate, nitrate and ammonium during a haze episode (Case 2) was faster than that during a clean episode (CE), owing to exacerbated effects of PM2.5 acidity in the event of high relative humidity (RH) on hazy days. Finally, the detected significant correlations of [NO3−]/[SO42−] with [NH4+]/[SO42−] in conditions of abundant NH4+ indicate that NO3− in Shanghai is primarily formed through homogeneous reaction between ambient NH3 and HNO3. These findings provide new perspectives on our interpretation of PM2.5 acidity during haze episodes in megacities.

Comparison of Ammonia Emission Estimation between Passive Sampler and Chamber System in Paddy Soil after Fertilizer Application

Ammonia (NH3) is an important precursor for particulate secondary aerosol formation. This study was conducted to evaluate the applicability of a passive sampler (PAS) for estimating the NH3 emission from chemical fertilizer application (85 kg-N·ha−1) at field scale and to compare the results with a chamber system for the calculation of NH3 emission flux at lab scale. The application of chemical fertilizer increased the ambient NH3 concentration from 7.11 to 16.87 μg·m−3. Also, the ambient NH3 concentration measured by the PAS was found to be highly influenced by not only the chemical fertilizer application but also the weather (temperature and rainfall). Wind rose diagram data can be useful for understanding the distribution of ambient NH3 concentration. In the case of a chamber with few environmental variables, NH3 was emitted very quickly in the early stages and gradually decreased, whereas it was delayed at intervals of about one week at the site. It was found that daily temperature range, atmospheric disturbance by wind and rainfall, changes in soil moisture, and the presence of a flooded water table were the main influencing factors. The PAS data and the chamber system data were observed to have significant differences in spatial-temporal scale. In order to reduce the gap, it seems to be necessary to further develop a chamber system, in order to improve the precision of field analysis and to strengthen the connection between experimental results.

Aqueous electrocatalytic N2 reduction for ambient NH3 synthesis: recent advances in catalyst development and performance improvement

In this review, we summarize recent advances in the design and development of electrocatalysts for the N2 reduction reaction. We also discuss the strategies to boost catalytic performances, the methods for reliable NRR experiments, and perspectives for further research directions.

Tracking down global NH₃ point sources with wind-adjusted superresolution

As a precursor of atmospheric aerosols, ammonia (NH3) is one of the primary gaseous air pollutants. Given its short atmospheric lifetime, ambient NH3 concentrations are dominated by local sources. In a recent study, Van Damme et al. (2018) have highlighted the importance of NH3 point sources, especially those associated with feedlots and industrial ammonia production. Their emissions were shown to be largely underestimated in bottom-up emission inventories. The discovery was made possible thanks to the use of oversampling techniques applied to 9 years of global daily IASI NH3 satellite measurements. Oversampling allows one to increase the spatial resolution of averaged satellite data beyond what the satellites natively offer. Here we apply for the first time superresolution techniques, which are commonplace in many fields that rely on imaging, to measurements of an atmospheric sounder, whose images consist of just single pixels. We demonstrate the principle on synthetic data and on IASI measurements of a surface parameter. Superresolution is a priori less suitable to be applied on measurements of variable atmospheric constituents, in particular those affected by transport. However, by first applying the wind-rotation technique, which was introduced in the study of other primary pollutants, superresolution becomes highly effective in mapping NH3 at a very high spatial resolution. We show that plume transport can be revealed in greater detail than what was previously thought to be possible. Next, using this wind-adjusted superresolution technique, we introduce a new type of NH3 map that allows tracking down point sources more easily than the regular oversampled average. On a subset of known emitters, the source could be located within a median distance of 1.5 km. We subsequently present a new global point-source catalog consisting of more than 500 localized and categorized point sources. Compared to our previous catalog, the number of identified sources more than doubled. In addition, we refined the classification of industries into five categories – fertilizer, coking, soda ash, geothermal and explosives industries – and introduced a new urban category for isolated NH3 hotspots over cities. The latter mainly consists of African megacities, as clear isolation of such urban hotspots is almost never possible elsewhere due to the presence of a diffuse background with higher concentrations. The techniques presented in this paper can most likely be exploited in the study of point sources of other short-lived atmospheric pollutants such as SO2 and NO2.

Tracking down global NH₃ point sources with wind-adjusted superresolution

As a precursor of atmospheric aerosols, ammonia (NH3) is one the primary gaseous air pollutants. Given its short atmospheric lifetime, ambient NH3 concentrations are dominated by local sources. In a recent study, Van Damme et al. (2018) have highlighted the importance of NH3 point sources, especially those associated with feedlots and industrial ammonia production. Their emissions were shown to be largely underestimated in bottom-up emission inventories. The discovery was made possible thanks to the use of oversampling techniques applied on 9 years of global daily IASI NH3 satellite measurements. Oversampling allows to increase the spatial resolution of averaged satellite data, beyond what the satellites natively offer. Here, we apply for the first time the so-called superresolution techniques, which are commonplace in many fields that rely on imaging, to measurements of an atmospheric sounder, whose images consist of just single pixels. We demonstrate the principle on synthetic data and on IASI measurements of a surface parameter. Superresolution is a priori less suitable to be applied on measurements of variable atmospheric constituents, in particular those affected by transport. However, by first applying the so-called wind-rotation technique, which was introduced in the study of other primary pollutants, superresolution becomes highly effective to map NH3 at very high spatial resolution. We show in particular that it allows revealing plume transport in much greater detail than what was previously thought to be possible. Next, using this wind-adjusted superresolution technique, we introduce a new type of NH3 map that allows to track down point sources much more easily than the regular oversampled average. On a subset of known emitters, it allows to locate the source within a median distance of 1.5 km. We subsequently present a new global point source catalog consisting of more than 500 localized and categorized point sources. Compared to our previous catalog, the number of identified sources more than doubled. In addition, we refined the classification of industries into five categories: fertilizer, coking, soda ash, geothermal and explosive industry; and introduced a new urban category for isolated NH3 hotspots over cities. The latter mainly consists of African megacities, as clear isolation of such urban hotspots is almost never possible elsewhere due to the presence of a larger diffuse background. The techniques presented in this paper can most likely be exploited in the study of point sources of other short-lived atmospheric pollutants such as SO2 and NO2.

Ultrasmall V8C7 nanoparticles embedded in conductive carbon for efficient electrocatalytic N2 reduction toward ambient NH3 production

Vanadium carbide nanoparticles/carbon acts as an efficient NRR electrocatalyst in 0.1 M HCl, achieving a large NH3 yield of 34.62 μg h−1 mgcat.−1 and a high FE of 12.20%.