High Concentrations Of NH4 Research Articles

COMPREHENSIVE CHARACTERISATION OF TEMPORAL VARIATIONS IN CONCENTRATIONS OF GASEOUS AMMONIA AND NITROGEN OXIDES IN TYPICAL URBAN ATMOSPHERE

Atmospheric ammonia (NH3) is a well-known contributor to secondary particle formation and canlead to severe environmental degradation and human health outcomes. In the context of the verylimited knowledge about updated data on NH3 levels in urban areas, this paper presents the results ofa one-year (Apr 2023 – Mar 2024) measurement campaign of NH3 concentrations conducted at theurban background site in Zabrze, located in the central part of the Upper Silesian Industrial District(USID) (southern Poland), which could be considered one of the European hotspots. The research wasperformed using an automatic ammonia analyzer Model T201 by Teledyne API, which provides dataon the levels of NH3 and other gaseous nitrogen compounds (NO (nitrogen oxide), NO2 (nitrogendioxide), NOx (nitrogen oxides) at hourly time resolution. Consequently, this enabled an analysisof specific temporal variations of NH3 concentrations, and therefore allowed the identification ofits possible emission sources and insight into processes involving ammonia. The results obtained inthis study revealed that ammonia stood out from nitrogen oxides and other atmospheric pollutants– with high NH3 concentrations recorded during spring and summer, which is related to the highintensity of gaseous NH3 formation under warm meteorological conditions. A different situationwas observed in the hourly NH3 concentration distribution scheme, which was manifested by muchless visible diurnal variations of NH3 levels, with no characteristic morning maximum, as well asthe occurrence of a broad afternoon maximum in the summer. In summary, anthropogenic sourceshad a significant impact on NH3 concentrations in the area under consideration, with a greater roleof traffic in the case of NOx, and a biomass and fossil fuel combustion and/or industrial sources –for NH3. Local meteorological conditions also had a notable influence on NH3 levels, of which airtemperature (positive correlation) and wind speed (negative correlation) were found to be the mostimportant. The ongoing research is planned to be continued, as it can provide valuable scientific datafor the development of air quality protection strategies and programmes in urban areas, especially inthe field of reducing emissions of gaseous precursors of particulate matter.

Isolation and characterization of mung bean (Vigna radiata L.) rhizobia in Myanmar

AbstractWe collected soil samples from six major mung bean cropping regions in Myanmar: Sagaing, Mandalay, Nay Pyi Taw, and Magway in the tropical savanna climate zone and Bago and Yangon in the tropical monsoon climate zone. All fields grew mung bean for at least 5 years and had no history of rhizobial inoculation. Mung bean ‘Yezin-11’, a popular cultivar in Myanmar, was inoculated with soil suspensions. From the nodules formed on the roots, we isolated 55 rhizobial strains. Identification of the isolates revealed the dominant species of indigenous rhizobia in each region. We identified 53 Bradyrhizobium strains and 2 Ensifer strains. Bradyrhizobium yuanmingense was dominant in the tropical savanna zone and Bradyrhizobium sp. (B. liaoningense or B. diversitatis) and B. centrosematis were dominant in the tropical monsoon zone. Principal component analysis indicates that the dominance of B. yuanmingense in the tropical savanna zone might be due to high concentration of NO3-N and P2O5 in the soil. It also indicates that the dominance of B. centrosematis in the tropical monsoon zone might be caused by drastically low pH and high concentration of NH4 in the soil. Bradyrhizobium centrosematis YGN-M9, B. yuanmingense SGG-M3, and Bradyrhizobium sp. BGO-M5 significantly increased nodulation (nodule number and nodule dry weight), acetylene reduction activity, and shoot dry weight, respectively, relative to Ensifer terangae MDY-M6. Co-inoculation with these three strains increased nodulation significantly compared with single inoculation of BGO-M5. The characterization of mung bean rhizobia and selection of microbial inoculant candidates will be useful for the development of microbial inoculants in Myanmar.

Remediation of heavy metal contaminated soil in mining areas with vaterite-type biological calcium carbonate

In recent years, research on the remediation of heavy metal contaminated soil by microbially induced carbonate precipitation (MICP) technology has yielded significant findings. However, when utilizing MICP for remediation in situ, urea and calcium chloride may produce high concentrations of NH4+ and Cl-, which subsequently cause secondary pollution. If the biological calcium carbonate (Bio-CaCO3) produced by MICP is employed as a highly efficacious adsorbent, secondary pollution can be avoided while remediating heavy metal pollution. In this study, vaterite-type Bio-CaCO3 was prepared under the regulation of sophorolipids, and the remediation effect and mechanisms for heavy metal contaminated soil were investigated. The results demonstrated that sophorolipids facilitate the formation and stabilization of vaterite-type Bio-CaCO3. The addition of vaterite-type Bio-CaCO3 could notably increase the content of soil organic matter, enhance soil urease activity, and reduce soil catalase activity. On the 30th day of remediation with vaterite-type Bio-CaCO3, the active state content of Pb and Cd in the soil exhibited a decrease of 41.23% and 35.00%, respectively. Additionally, the exchangeable state content demonstrated a reduction of 6.61% and 8.48%, while the carbonate-bound state exhibited an increase of 12.05% and 13.89%, respectively. The principal mechanisms for the remediation of heavy metal contaminated soil by vaterite-type Bio-CaCO3 may be attributed to ion exchange, chemical precipitation, physical adsorption, and complexation reactions. The analysis of the microbial community structure demonstrated that vaterite-type Bio-CaCO3 could enhance the abundance of multiple genera with urease-producing genes, including Pseudomonas, Staphylococcus, and Bacillus while maintaining the soil biodiversity. This study provides a new idea for the remediation of heavy metal contaminated soil around the mining area and offers technical support for the construction of green mines.

Investigating the convective transport possibilities of lower-atmospheric pollutants to the UTLS region using rainwater and aerosol chemical characterization

Various attempts using different platforms to understand the chemical composition of the Asian Tropopause Aerosol Layer (ATAL) have concluded that it primarily consists of nitrate (NO3−) aerosols. Recent in-situ measurements from aircraft flying through ATAL have suggested that ammonia (NH3) pollution from Asia could serve as the precursor for nitrate aerosols in ATAL through gas-to-particle formation after undergoing convective uplift to the Upper Troposphere and Lower Stratosphere (UTLS) regions. In this study, we aimed to investigate the potential pathways of convective transport of lower-atmospheric pollutants by analysing the chemical composition of rainwater and aerosols in a highly convective region, Kolkata (Head Bay of Bengal), India. We utilized the PILS-IC system established at Kolkata Camp Observatory of the National Atmospheric Research Laboratory (KCON). The analysis revealed a significant dominance of NH4+ and NO3− ions in both rainwater and aerosol samples during the monsoon and post-monsoon seasons, with the dominance increasing during the post-monsoon season. Air mass trajectories indicated a clear influence of the Indo-Gangetic Plain (IGP) region during the post-monsoon season, which is well-known for its dense agricultural activities and industries. High concentrations of NH3 even at higher altitudes, have been observed in Atmospheric Infrared Sounder (AIRS) measurements. Moreover, using Outgoing Longwave Radiation (OLR) and vertical wind as proxies for tropical deep convection and updrafts/downdrafts, respectively, we found evidence supporting the possibility of convective transport of these lower-atmospheric pollutants to the UTLS regions during the monsoon season. In conclusion, this study provides evidence for the potential convective transport of lower-atmospheric pollutants, including NH3 and other precursor gases, to higher levels. These pollutants could partially serve as the source of nitrate aerosols in the ATAL through gas-to-particle formation processes.

Inorganic Nitrogen Gas‐Aerosol Partitioning in and Around Animal Feeding Operations in Northeastern Colorado in Late Summer 2021

AbstractAmmonia (NH3) from animal feeding operations (AFOs) is an important source of reactive nitrogen in the US, but despite its ramifications for air quality and ecosystem health, its near‐source evolution remains understudied. To this end, Phase I of the Transport and Transformation of Ammonia (TRANS2Am) field campaign was conducted in the northeastern Colorado Front Range in summer 2021 and characterized atmospheric composition downwind of AFOs during 10 research flights. Airborne measurements of NH3, nitric acid (HNO3), and a suite of water‐soluble aerosol species collected onboard the University of Wyoming King Air research aircraft present an opportunity to investigate the sensitivity of particulate matter (PM) formation to AFO emissions. We couple the observations with thermodynamic modeling to predict the seasonality of ammonium nitrate (NH4NO3) formation. We find that during TRANS2Am northeastern Colorado is consistently in the NH3‐rich and HNO3‐limited NH4NO3 formation regime. Further investigation using the Extended Aerosol Inorganics Model reveals that summertime temperatures (mean: 23°C) of northeastern Colorado, especially near the surface, inhibit NH4NO3 formation despite high NH3 concentrations (max: ≤114 ppbv). Finally, we model spring/autumn and winter conditions to explore the seasonality of NH4NO3 formation and find that cooler temperatures could support substantially more NH4NO3 formation. Whereas NH4NO3 only exceeds 1 μg m−3 ∼10% of the time in summer, modeled NH4NO3 would exceed 1 μg m−3 61% (88%) of the time in spring/autumn (winter), with a 10°C (20°C) temperature decrease relative to the campaign.

Impact of p-cresol on hydrogen sulfide and ammonia treatment by biotrickling filter and the production of nitrous oxide

Biotrickling filter (BTF) is often used for purification of waste gas from swine houses, with vital information still needed regarding interaction effects among multiple gas pollutants removal and also the formation of byproducts especially nitrous oxide (N2O, a strong greenhouse gas) due to the relative high NH3 concentration level compared to other gases. In this study, gas removal and N2O production were compared between two BTFs, where the inlet gas of BTF-1 contained NH3 and H2S while p-cresol was additionally supplied to BTF-2. At inlet load (IL) between 3.67 and 18.91 g m−3 h−1, removal efficiencies of NH3 exceeded 95% for both BTFs. As alternative strategy, adding thiosulfate improved H2S removal. Interestingly, presence of p-cresol to some extent promoted H2S removal at IL of 0.56 g m−3 h−1possibly due to effect on pH value of circulating solution. Similar to NH3, removal efficiencies of p-cresol were higher than 95% at an average IL of 2.98 g m−3 h−1. Gas residence time, pH of circulating solution and inlet loading were identified as key factors affecting BTF performance, but the response of individual gas compound to these factors was not consistent. Overall, p-cresol enhanced N2O generation although the effects were not always significant. High-throughput sequencing results showed that Proteobacteria accounted for the largest proportion of relative abundance and BTF-2 had much richer microbial diversity compared to BTF-1. Thermomonas, Comamonas, Rhodanobacter and other bacterial genus capable of denitrification were detected in both BTFs, and their corresponding abundances in BTF-2 (10.9%, 8.7% and 5.2%) were all greater than those in BTF-1 (0.4%, 0.3% and 2.0%), indicating that more denitrification may occur within BTF-2 and higher N2O could have been generated. This study provided evidence that organic gas components, served as carbon source, may increase the N2O production from BTF when treating waste gases containing NH3.

Enhancement of Mn2+, Fe2+ and NH4+-N removal by biochar synergistic strains combined with activated sludge in real wastewater treatment

Acinetobacter sp. AL-6 combining with biochar was adapted in activated sludge (AS & co-system) to decontaminate Mn2+, Fe2+ and NH4+-N, and treat activated sludge (AS) for its activity and settling performance improvement. Specifically, the co-system promoted the growth of bacteria in the activated sludge, thus increasing its ability to nitrify and adsorb Mn2+ and Fe2+, resulting in the removal of high concentrations of NH4+-N, Mn2+, Fe2+ and COD in the reactor by 100%, 100%, 100%, and 96.8%, respectively. And the pH of wastewater was increased from 4 to 8.5 by co-system also facilitated the precipitation of Mn2+ and Fe2+. The MLVSS/MLSS ratio increased from 0.64 to 0.95 and SVI30 decreased from 92.54 to 1.54 after the addition of co-system, which indicated that biochar helped to improve the activity and settling performance of activated sludge and prevented it from being damaged by the compound Mn2+ and Fe2+. In addition, biochar promoted the increase of the tyrosine-like protein substance and humic acid-like organic matter in the sludge EPS, thus enhanced the ability of sludge to adsorb Mn2+ and Fe2+. Concretely, compared with AS group, the proteins content and polysaccharides content of the AS & co-system group were increased by 13.14 times and 6.30 times respectively. Further, microbial diversity analysis showed that more resistant bacteria and dominant bacteria Acinetobacter sp. AL-6 in sludge enhanced the nitrification and adsorption of manganese and iron under the promotion of biochar. Pre-eminently, the more effective AS & co-system were applied to the removal of actual electrolytic manganese slag leachate taken from the contaminated site, and the removal of NH4+-N, Mn2+, Fe2+ and COD remained high at 100%, 100%, 71.82% and 94.72%, respectively, revealing advanced value for high engineering applications of AS & co-system.

Carbohydrate addition strategy affects nitrogen dynamics, budget and utilization, and its microbial mechanisms in biofloc-based Penaeus vannamei culture

Biofloc technology (BFT) is a microbial biotechnology that has shown great potential in water quality control and nutrient re-utilization towards sustainable aquaculture. Carbohydrate addition is the main operation means for the application of BFT; however, we are still unclear how it affects microbial-driven nitrogen (N) transformation and utilization in BFT systems. In this study, autotrophic- and heterotrophic-dominated BFT systems (AS vs. HS) in triplicates were operated by two molasses addition strategies for a 13-week production trial of P. vannamei. Throughout the trial, more amount of bioflocs (in terms of VSS) were produced in HS than in AS. Higher concentrations of NH4+-N, NO2−-N, NO3−-N, TIN and TN while lower concentrations of TON were monitored in AS compared to HS. N budget analysis showed that the harvested shrimp deposited >34.4% of input N; and higher N retention in the final culture water while lower N loss and N discharge from the systems were found in AS compared to HS. Higher efficiencies of gross and feed N utilization were achieved in HS (36.6% and 38.8%) than in AS (34.5% and 34.9%). Metagenomic analysis revealed that abundant and diverse N-cycling microbial communities and functional genes in bioflocs constituted a complete and complex N-cycling network, which was the driving force of N transformation and recycling in the culture water of systems. The lower abundances of nitrifying bacteria and associated genes led to the inhibition of nitrification under high molasses addition in HS, which accounted for the differences in N dynamics, budget and utilization efficiency between AS and HS. Together, a quantitative model of N migration and transformation driven by N-cycling microbial communities of bioflocs was depicted in closed BFT systems for shrimp aquaculture. This study firstly revealed the N-cycling microbiome and functional effects in BFT systems, which provides theoretical and technical foundations for efficient N management in intensive aquaculture.

Emission Characteristics of Odorous Compounds from a Swine Farm on Jeju Island, Korea

This study investigated 26 malodorous substances emitted from a swine farm on Jeju Island, South Korea, to discern their specific emission characteristics and potential implications for workers’ health and environmental management. A detailed analysis of emissions from livestock buildings, the compost facility, and the manure storage tank was conducted. Accurate quantification involved rigorous collection methods measuring concentrations of NH3, hydrogen sulfide (H2S), trimethylamine (TMA), aldehyde compounds, volatile organic compounds (VOCs), volatile fatty acids (VFAs), p-cresol, indole, and skatole. High concentrations of NH3 and H2S, particularly in the manure storage tank, raised concerns about the health of workers. TMA levels were notably elevated in the livestock building, whereas aldehydes and VOCs remained within limits. VFAs were prevalent in the livestock building, with p-cresol, indole, and skatole in the manure storage tank. Distinct emission profiles across farm facilities highlight the need for tailored odor management strategies, ensuring worker well-being and effective environmental practices. These findings offer valuable insights for implementing targeted mitigation measures in similar agricultural settings.

Compartmentalization transformation of Fe2+, Mn2+ and NH4+ in groundwater: A comparative research containing experimental medium and functional genera profiling derived from experiment data

Contamination of soluble iron (Fe2+), manganese (Mn2+), and ammonium (NH4+) in groundwater is prevalent, particularly in Northeast China. This study aims to elucidate the intricate biological and physical-chemical reactions involved in the sequential transformation of three target contaminants. Two dynamic column simulations were used to compare quartz sand filtration (QSF) system with riverbank filtration (RBF) system to assess the interactions and respective contributions of the reactions involved in transforming process. Similar pattern of transformation vertical compartmentalization in two systems along the filter depth were founded, and the Fe2+ transformation was mainly distributed in the upper part, while NH4+ and Mn2+ occurred primarily in the downstream sections. The average transformation rate of Fe2+, Mn2+ and NH4+ in RBF system was 84.52 %, 47.68 % and 67.95 %, respectively, which was 5.20 %, 11.43 % and 23.06 % higher than in QSF system. The dominant transformation process for Fe2+ in RBF involved chemical oxidation, bio-oxidation and adsorption. The lower transformation rate for Mn2+ was attributed to abiotic homogenous oxidation limitation and negative affect derived from high concentration of NH4+ with high nitrification rate in RBF system. Nitrification by Nitrosomonas and Nitrospira was critical NH4+ transformation mechanism in RBF system, while the adsorption by iron and manganese oxide and aerobic denitrification were contributed strongly to NH4+ transformation in QSF system. Furthermore, the spatial distribution of functional bacterial genera was in good consistent with the transformation compartmentalization of three target contaminants in both systems, and similar microbial community structure reflected the domestication effect of groundwater chemistry on functional bacteria.

Effects of flow rate and wastewater concentration on the transformation of nitrogen in sediment-water system of sewage pipelines.

In this work, the transformation law of nitrogen in sediment-water system under different flow rates and wastewater concentrations were investigated in a simulated sewage pipeline system. Results showed that the different flow rates and wastewater concentrations in the pipeline caused differences in microbial community in sediments and nitrogen transformation. When the flow rate increased from 0.05 to 0.2 m/s, the scouring effect was enhanced, resulting in higher concentrations of NH4 + -N and NO3 - -N in the overlying water. At 0.2 m/s, the relative abundance of Clostridium_sensu_stricto_1 in sediments was higher, resulting in a greater conversion of amino acid nitrogen (AAN) to NH4 + -N. Meanwhile, many denitrifying bacteria (Trichococcus, Dechloromonas, norank_f__norank_o__Gaiellales, Thiobacillus) had high relative abundance in the sediments, and the denitrification process was common. When the wastewater concentration was high, the nitrification reaction was great in overlying and interstitial water. Moreover, the ammoniation process was great in the sediments, and the variation flux of AAN was large (remarkably reduced). PRACTITIONER POINTS: AAN transformed to NH4 + -N in sediment under different flow rate and concentration. Scouring was enhanced at 0.2 m/s, increasing nitrogen contents in overlying water. Difference in microbial community led to more AAN conversion to NH4 + -N at 0.2 m/s. The ammoniation process was greater in sediment at a high concentration of sewage. NH4 + -N migrated from overlying water to sediment at a high concentration of sewage.

Functional leaf-trait variability and herbivory in oaks along a Mexican avocado agrosystem mosaic

Land-use changes transforming forested landscapes to avocado orchards affect abiotic conditions and ecological processes. As a consequence, such changes can also affect leaf functional traits expression of co-occurring trees in orchards and related plant–insect interactions. Here, we evaluated changes in chemical soil properties and the effects of micro-climatic variables on leaf functional traits and herbivory in Quercus castanea and Q. obtusata in fragments occurring in a mosaic with avocado orchards. We differentiate three cases: forest cover > orchards, forest cover = orchards and forest cover < orchards in Michoacan state, Mexico. In each case, at least 17 individuals of each oak species were selected to analyze leaf functional traits and herbivory. Soil samples were collected to analyze chemical properties. Soils of areas with higher proportion of forest had higher concentrations of NH4+ and K+, whereas soils with higher proportion of orchards displayed higher concentrations of Mg2+, NO3− and SO42−. Leaf thickness, fresh mass and water content were higher in areas with higher forest cover and were influenced by Mg2+, NO3−, SO42- and local climatic variables. Leaf dry weight, specific leaf area, leaf area and chlorophyll content, as well as herbivory were higher in areas with higher proportions of orchards and were affected by PO43−, total P, K+, NH4+, and by local climatic variables. These results highlight the responses and links of plant functional traits associated with soil properties and local climatic variables and their possible consequences of biotic interactions in a landscape mosaic with different covers of avocado orchards and temperate forests.

The Influence of Meteorological Factors and the Time of Day on the Concentration of Ammonia in the Atmosphere Measured Using the Photoacoustic Method near a Cattle Farm—A Case Study

Influences of animals, time of day, air temperature and relative humidity, wind speed and direction on ammonia concentrations were investigated. A case study on a typical summer day from 7:00 to approximately 24:00 CEST (moderate wind speed, variable cloudiness and maximum global radiation higher than 950 W/m2) in west–central Poland is presented. Concentrations of this gas were measured at four heights (0.1–1.5 m), which were changed every 5 min, using a Nitrolux 1000 photoacoustic spectrometer. A micrometeorological station was established to also measure the surface energy budget components. The results presented are the average for each hour and for the entire day. The fine structure of concentration profiles, plume detection and uncertainty of ammonia flux calculation are also presented. The highest NH3 concentrations were at a 0.5 m height between 16:00 and 17:00 h when cows were grazing, but the lowest concentrations were between 23:00 and 24:00 h at the height of 1.5 m. The ammonia concentration increased with increasing air temperature and was the highest with a westerly wind direction and decreased with increasing air relative humidity. The greatest influence on the ammonia concentration was related to the presence of cows and the time of day, while a slightly smaller influence was noted in terms of air temperature and wind direction. A case study is suitable for presenting local effects, inhomogeneities and quantifying uncertainties in the bidirectional ammonia flux calculation.

In situ biomass burning enhanced the contribution of biogenic sources to sulfate aerosol in subtropical cities

Sulfurous gases released by biogenic sources play a key role in the global sulfur cycle. However, the contribution of biogenic sources to sulfate aerosol in the urban atmosphere has received little attention. Emission sources and formation process of sulfate in Guangzhou, a subtropical mega-city in China, were clarified using multiple methods, including isotope tracers and chemical markers. The δ18O of sulfate suggested that secondary sulfate was the dominant component (84 %) of sulfate aerosol, which mainly formed by transition metal ion (TMI) catalyzed oxidation (31 %) and OH radical oxidation (30 %). The factors driving secondary sulfate formation were revealed using a tree boosting model, which suggested that NH3, temperature, and oxidants were the most important factors. The δ34S of sulfate indicated that biogenic sources accounted for annual average of 26.0 % of the sulfate, which increased to 30.4 % in winter monsoon period. Rice straw burning enhanced sulfate formation by promoting the release of reduced sulfur from soil, which is rapidly converted into sulfate under a subtropical urban atmosphere with high concentration of NH3 and oxidants. This study revealed the important influence of rice straw burning on biogenic sulfur emission during the rice harvest, thereby providing insight into the sulfur cycle and regional air pollution.

Ammonia as a Marine Fuel towards Decarbonization: Emission Control Challenges

Decarbonization of the maritime sector to achieve ambitious IMO targets requires the combination of various technologies. Among alternative fuels, ammonia (NH3), a carbon-free fuel, is a good candidate; however, its combustion produces NOx, unburnt NH3 and N2O—a strong greenhouse gas (GHG). This work conducts a preliminary assessment of the emission control challenges of NH3 application as fuel in the maritime sector. Commercial catalytic technologies are applied in simulated NH3 engine exhaust to mitigate NH3 and NOx while monitoring N2O production during the reduction processes. Small-scale experiments on a synthetic gas bench (SGB) with a selective-catalytic reduction (SCR) catalyst and an ammonia oxidation catalyst (AOC) provide reaction kinetics information, which are then integrated into physico-chemical models. The latter are used for the examination of two scenarios concerning the relative engine-out concentrations of NOx and NH3 in the exhaust gas: (a) shortage and (b) excess of NH3. The simulation results indicate that NOx conversion can be optimized to meet the IMO limits with minimal NH3 slip in both cases. Excess of NH3 promotes N2O formation, particularly at higher NH3 concentrations. Engine-out N2O emissions are expected to increase the total N2O emissions; hence, both sources need to be considered for their successful control.

Study on the mechanism of nitrogen conversion in NH3-doped methane premixed flame based on multi-spectral analysis methods

It is essential to obtain the in-situ key radicals and components in the combustion process of NH3 oxidation to reveal the volatile nitrogen conversion mechanism. In this work, multi-spectral analysis methods, including image spectroscopy, Tunable diode laser absorption spectroscopy (TDLAS), and plane laser-induced fluorescence (PLIF) were used to obtain the spatial distribution characteristics of the main excited radicals (C2*/CH*/CN*/OH*), H2O, and NO in NH3-doped methane flames, respectively. Furthermore, the kinetic simulation was combined to obtain the key reactions and main pathways of nitrogen conversion. The experimental results showed that when the concentration of NH3 was low, the NO generated in lean flame was less than that in rich flame, which was more than that in rich flame when the concentration of NH3 was high. NH3 also promoted the formation of H2O in flames. The image spectral intensity of CN* had a significant linear relationship with the CN concentration obtained by simulation, indicating that CN* was mainly generated by CN thermal excitation. The results of sensitivity and path analysis indicated that rich flame contributed to the reaction of N-species with H and that high NH3 concentration promoted the conversion of NH2 to HNO. With increasing NH3 concentration and equivalence ratio, the proportion of CH3 conversion to C2H6 was enhanced, while the proportion of CH3 oxidized decreased. This work reveals the mechanism of volatile nitrogen (NH3) conversion and the influence of equivalence ratio and NH3 concentration on it, which provides theoretical guidance for NOx emission reduction.

Underestimated ammonia vehicular emissions in metropolitan city revealed by on-road mobile measurement

Atmospheric ammonia (NH3) plays a significant role in the nitrogen cycle, and can have impacts on air quality, ecological balance and climate change. While NH3 associated with natural and agricultural processes has long been considered the primary source, the contribution of combustion-related NH3, particularly from vehicular emissions, keeps on the rise. We found that high on-road NH3 concentrations occurred in a metropolitan city based on mobile measurement, and inferred that urban vehicular NH3 emission was likely underestimated in the past. NH3 emission factors (EFs) were derived from ring roads and tunnels, showing levels 74% and 20% higher than the latest standard proposed by Euro VII, respectively. To quantify the underestimation, two methods based on car ownership and traffic flow were used to estimate the annual vehicular NH3 emission in Shanghai as 2.59 and 1.76 Gg, respectively, substantially surpassing the predicted results by the Dynamic Projection model for Emissions in China. Given these discoveries, we recommend that it is urgent and imperative to establish relevant national standards and limits aiming at regulation on vehicular NH3 emissions. And more representative EFs measurements should be adopted to improve the accuracy of inventory estimation.

Zebrafish as a biological model for assessing water quality along tropical hydrographic river basins in Northeast Brazil.

Tropical rivers are the main destinations for tailings from urban, industrial and agricultural activities in the region studied. The present study aimed to investigate if early stages of zebrafish (Danio rerio) development is a viable biological model to assess the toxicity of surface waters of tropical rivers, and whether that toxicity could be correlated to standard water quality indexes. Embryos were exposed to samples from 55 sites from 10 hydrographic basins of rivers in Pernambuco State, northeastern Brazil. Lethality rates, sublethal toxicity based on the general morphology score (GMS) and frequencies of abnormalities were analyzed. Significant mortality was observed in samples of 7 basins. The GMS indicated significant delay in embryo-larval development in 50% of the samples. The highest toxicity was detected in basins within Recife metropolitan area, where 61% of the samples caused sublethal toxicity. Most frequent developmental abnormalities included non-inflation of the swim bladder, delayed hatching and blood stasis. The highest frequencies of blood stasis were detected in samples with highest NH3 concentrations, corroborated by a positive correlation suggesting the existence of a causal relationship. A significant correlation was detected between water quality indexes and GMS with a greater toxic effect being observed in samples collected in areas of greater urban density and greater contamination by domestic sewage. This study demonstrates that the early stages of the zebrafish is a viable ecotoxicological model to assess the toxicity of surface waters and can contribute to a better understanding between the chemical composition and the adverse effects suffered by fish early life stage fish in tropical rivers.

Transport and distribution of residual nitrogen in ion-adsorption rare earth tailings

A large amount of nitrogen remains in ion-absorption rare earth tailings with in-situ leaching technology, and it continually ends up in groundwater sources. However, the distribution and transport of ammonium nitrogen (NH4+-N) and nitrate nitrogen (NO3−-N) across tailings with both depth and hill slopes is still unknown. In this study, the amount of NH4+-N and nitrate nitrogen (NO3−-N) was determined in tailings, and a soil column leaching experiment, served to assess the transport and distribution following mine closure. Firstly, a high concentration of NH4+-N in the leachate at the initial leaching stage was detected, up to 2000 mg L−1, and the concentration of NH4+-N clearly diminished as time passed. Meanwhile, the NH4+-N contents remained relatively high in soil. Secondly, both the content of NH4+-N and NO3−-N varied greatly according to vertical distribution after leaching lasting several years. The amounts of NH4+-N and NO3−-N in surface soil were much smaller than those in deep soil, with 3–4 orders of magnitude variation with depth. Thirdly, when disturbed by NH4+-N, the pH not only diminished but also changed irregularly as depth increased. Fourthly, although the amount of NO3−-N was smaller than that of NH4+-N, both their distribution trend was similar with depth. In fact, NH4+-N and NO3−-N were significantly correlated but this declined from the knap to the piedmont. Based on these results, it is suggested that mining activity could cause nitrogen to be dominated by NH4+-N and acidification in a tailing even if leaching occurs over several years. NO3−-N derived from NH4+-N transports easily and it becomes the main nitrogen pollutant with the potential to be a long-lasting threat to the environment around a mine.

Seasonal and regional variations of atmospheric ammonia across the South Korean Peninsula

This study aimed to identify the factors causing NH3 emissions in the South Korean Peninsula and West Sea region. To analyze the trends of NH3 and other air pollutants, such as NOx, CO, and NR-PM1, we collected samples from six supersites across the peninsula, a roadside in Seoul, and the West Sea over different sampling periods, ranging from 1 month to 1 year. The highest NH3 concentrations were found at rural areas, ascribed to agricultural activities, particularly NH4NO3 decomposition at high summer temperatures. Areas with low population densities recorded the lowest NH3 concentrations, attributed to the lack of anthropogenic activities. A roadside field experiment confirmed the close link between ambient NH3 and vehicle emissions in urban regions by showing a strong correlation between CO and NOx concentrations and that of NH3. Moreover, we examined oceanic emissions near the eastern coast of South Korea in the West Sea. Long-range transportation studies confirmed that most of the pollutants (NH3, CO, and PM1) were transported by wind from the northeastern region of China. A maritime origin study showed that oceanic emissions and NH4NO3 decomposition in the atmosphere owing to high temperatures were the causing NH3 pollution. These findings provided valuable insights into the emission sources of NH3 in primary air pollutants in South Korea, highlighting the contributions of land-based and oceanic sources. Our study can help inform policymakers and stakeholders for developing effective regional air pollution control strategies.