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The global inventory of NO x (NO x = NO + NO2) emissions is poorly constrained, with a large portion of the uncertainty attributed to soil NO emissions that result from soil abiotic and microbial processes. While natural abundance stable N isotopes (?15N) in various soil N-containing compounds have proven to be a robust tracer of soil N cycling, soil ?15N-NO is rarely quantified due to the measurement difficulties. Here, we present a new method that collects soil-emitted NO through NO conversion to NO2 in excess ozone (O3) and subsequent NO2 collection in a 20% triethanolamine (TEA) solution as nitrite and nitrate for ?15N analysis using the denitrifier method. The precision and accuracy of the method were quantified through repeated collection of an analytical NO tank and intercalibration with a modified EPA NO x collection method. The results show that the efficiency of NO conversion to NO2 and subsequent NO2 collection in the TEA solution is >98% under a variety of controlled conditions. The method precision (1?) and accuracy across the entire analytical procedure are ±1.1‰. We report the first analyses of soil ?15N-NO (-59.8‰ to -23.4‰) from wetting-induced NO pulses at both laboratory and field scales that have important implications for understanding soil NO dynamics. [ABSTRACT FROM AUTHOR]

Indirect nitrous oxide (N 2 O) emissions from streams and rivers are a poorly constrained term in the global N 2 O budget. Current models of riverine N 2 O emissions place a strong focus on denitrification in groundwater and riverine environments as a dominant source of riverine N 2 O, but do not explicitly consider direct N 2 O input from terrestrial ecosystems. Here, we combine N 2 O isotope measurements and spatial stream network modeling to show that terrestrial-aquatic interactions, driven by changing hydrologic connectivity, control the sources and dynamics of riverine N 2 O in a mesoscale river network within the U.S. Corn Belt. We find that N 2 O produced from nitrification constituted a substantial fraction (i.e., >30%) of riverine N 2 O across the entire river network. The delivery of soil-produced N 2 O to streams was identified as a key mechanism for the high nitrification contribution and potentially accounted for more than 40% of the total riverine emission. This revealed large terrestrial N 2 O input implies an important climate-N 2 O feedback mechanism that may enhance riverine N 2 O emissions under a wetter and warmer climate. Inadequate representation of hydrologic connectivity in observations and modeling of riverine N 2 O emissions may result in significant underestimations.

Coal thermal and kinetic parameters are important for the design of combustion reactors and risk assessment. Two methods were employed to investigate such key parameters of lignite, bituminous, and anthracite coal samples from China. With thermogravimetry (TG) and differential scanning calorimetry (DSC) methods, two distinct transitional stages were found in all coal samples combustion, but reaction intervals shifted to higher temperatures from lignite to anthracite and varied between 317 and 665 °C depending on the sample nature. Compared to the other two coal types, the pyrolysis of anthracite was less sensitive to increasing temperature, and its combustion process occurred at a much higher temperature. The results indicated that anthracite is difficult to ignite but has a considerable heat of reaction of 22.6 kJ/kg if ignited, which is close to that of bituminous. The basket heating method was used to obtain the kinetic data. Sample activation energies varied in the ranges of 38-51 kJ/mol from TG analysis and 49-67 kJ/mol from basket heating tests. Both results were comparable and consistent with the reference data. Due to its higher activation energy, anthracite poses a lower risk of thermal runaway than other coal types. This conclusion was validated by performing a minimum ignition temperature determination of a dust layer (MITL). In contrast, lignite and bituminous should be handled with greater safety precautions in coal-related process industries. The data presented will be used for hazard analysis and for designing more efficient combustion reactors in power plants. The data collected led to an extension of the current data for coal dust, as found in the literature., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

Rivers and streams contribute significant quantities of methane (CH 4 ) to the atmosphere. However, there is a lack of CH 4 flux and ebullitive (bubble) emission data from urban rivers, which might lead to large underestimations of global aquatic CH 4 emissions. Here, we conducted high-frequency surveys using the boundary layer model (BLM) supplemented with floating chambers (FCs) and bubble traps to investigate the seasonal and diurnal variability in CH 4 emissions in a eutrophic urban river and to evaluate whether the contribution of bubbles is important. We found that ebullition contributed nearly 99% of CH 4 emissions and varied on hourly to seasonal time scales, ranging from 0.83 to 230 mmol m -2 d -1 , although diffusive emissions and CH 4 concentrations in bubbles did not exhibit temporal variability. Ebullitive CH 4 emissions presented high temperature sensitivity ( r = 0.6 and p < 0.01) in this urban river, and eutrophication might have triggered this high temperature sensitivity. The ebullitive CH 4 flux is more likely to be underestimated at low temperatures because capturing the bubble flux is more difficult, given the low frequency of ebullition events. This study suggests that future ebullition measurements on longer time scales are needed to accurately quantify the CH 4 budgets of eutrophic urban rivers.

Nitrification is a crucial step in ecosystem nitrogen (N) cycling, but scaling up from plot-based measurements of gross nitrification to catchments is difficult. Here, we employed a newly developed method in which the oxygen isotope anomaly (Δ 17 O) of nitrate (NO 3 - ) is used as a natural tracer to quantify in situ catchment-scale gross nitrification rate (GNR) for a temperate forest from 2014 to 2017 in northeastern China. The annual GNR ranged from 71 to 120 kg N ha -1 yr -1 (average 94 ± 10 kg N ha -1 yr -1 ) over the 4 years in this forest. This result and high stream NO 3 - loss (4.2-8.9 kg N ha -1 yr -1 ) suggest that the forested catchment may have been N-saturated. At the catchment scale, the total N output of 10.7 kg N ha -1 yr -1 , via leaching and gaseous losses, accounts for 56% of the N input from bulk precipitation (19.2 kg N ha -1 yr -1 ). This result indicates that the forested catchment is still retaining a large fraction of N from atmospheric deposition. Our study suggests that estimating in situ catchment-scale GNR over several years when combined with other conventional flux estimates can facilitate the understanding of N biogeochemical cycling and changes in the ecosystem N status.

Infant formula (IF) requires a strict microbiological standard because of the high vulnerability of infants to foodborne diseases. The current study used the PacBio single-molecule real-time (SMRT) sequencing platform to generate full-length 16S rRNA-based bacterial microbiota profiles of 30 Chinese domestic and imported IF samples. A total of 600 species were identified, dominated by Streptococcus thermophilus, Lactococcus lactis, and Lactococcus piscium. Distinctive bacterial profiles were observed between the two sample groups, as confirmed with both principal coordinate analysis and multivariate analysis of variance. Moreover, the product whey protein nitrogen index (WPNI), representing the degree of preheating, negatively correlated with the relative abundances of the Bacillus genus. This study has demonstrated the application of the PacBio SMRT sequencing platform in assessing the bacterial contamination of IF products, which is of interest to the dairy industry for effective monitoring of microbial quality and safety during production.