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Greenhouse gases (GHGs) like nitrous oxide (N2O), carbon dioxide (CO2), and methane (CH4) are both emitted and removed by soils. Accurate worldwide allocations of carbon budget are essential for land use planning, global climate change, and climate-related research. Precise measurements, drivers, and mitigation strategies are necessary, given agricultural soil's significant potential storage and emission capacities. Different agricultural management practices cause greenhouse gas (GHG) emissions into the atmosphere and contribute to anthropogenic emissions. Agricultural soils can generate 70% of the world's manmade N2O emissions and also behave as a CO2 sink and a source of organic carbon and as producers and consumers of CH4. When it comes to agronomic management, the source and sink of all these GHGs are distinct. Therefore, several approaches to measuring GHG emissions from agricultural soils are available and can be categorized into chamber systems and remote sensing approaches. Sustainable agriculture stands out as a viable and transformative approach to increase agricultural efficiency while addressing the challenge of GHG emissions. Incorporating advanced technologies, precise data analytics, and site-specific management practices can offer a pathway to mitigate GHG emissions, thereby reducing the global warming potential (GWP). Therefore, this review paper focuses solely on the drivers influencing and involving soil emissions and on quantification approaches for GHG emissions. In addition, mitigation practices aimed at optimizing GHG emissions from agricultural soils are highlighted. [ABSTRACT FROM AUTHOR]

Solar radiation triggers atmospheric nitrous acid (HONO) photolysis, producing OH radicals, thereby accelerating photochemical reactions, leading to severe secondary pollution formation. Missing daytime sources were detected in the extensive HONO budget studies carried out in the past. In the rural North China Plain, some studies attributed those to soil emissions and more recent studies to dew evaporation. To investigate the contributions of these two processes to HONO temporal variations and unknown production rates in rural areas, HONO and related field observations obtained at the Gucheng Agricultural and Ecological Meteorological Station during spring and autumn were thoroughly analyzed. Morning peaks in HONO frequently occurred simultaneously with those of ammonia (NH3) and water vapor both during spring and autumn, which were mostly caused by dew and guttation water evaporation. In spring, the unknown HONO production rate revealed pronounced afternoon peaks exceeding those in the morning. In autumn, however, the afternoon peak was barely detectable compared to the morning peak. The unknown afternoon HONO production rates were attributed to soil emissions due to their good relationship to soil temperatures, while NH3 soil emissions were not as distinctive as dew emissions. Overall, the relative daytime contribution of dew emissions was higher during autumn, while soil emissions dominated during spring. Nevertheless, dew emission remained the most dominant contributor to morning time HONO emissions in both seasons, thus being responsible for the initiation of daytime OH radical formation and activation of photochemical reactions, while soil emissions further maintained HONO and associated OH radial formation rates at a high level, especially during spring. Future studies need to thoroughly investigate the influencing factors of dew and soil emissions and establish their relationship to HONO emission rates, form reasonable parameterizations for regional and global models, and improve current underestimations in modeled atmospheric oxidation capacity. [ABSTRACT FROM AUTHOR]

Boreal forest ecosystems are regions vulnerable to climate change. Such areas act as the main atmospheric carbon sinks in the world. Wildfires are among the drivers of ecosystem modification and functioning. Boreal wildfires emit an annual average of about 10% of global fire emissions. Taking into account recent climate warming and increases in the frequency of wildfires, boreal forests might switch their functional role from carbon sink to an additional source of atmospheric carbon. Soil respiration is the second largest component of the global carbon cycle and is highly sensitive to disturbance factors, including wildfires. To study the effect of wildfires on soil CO2 emission rates, the fire chronosequence was investigated. During the first few years following the fire, the soil CO2 emission rates were lower compared with the usual levels. It was found that 23 years after a fire, the site demonstrated transition behavior in soil emission rates between disturbed and completely recovered areas. The emission rates at the earliest successional stages are mainly controlled by soil moisture during the summer period. For the other successional stages, soil temperature had a huge impact on soil emission. [ABSTRACT FROM AUTHOR]

Solar radiation triggers atmospheric nitrous acid (HONO) photolysis, producing OH radicals, thereby accelerating photochemical reactions, leading to severe secondary pollution formation. Missing daytime sources were detected in the extensive HONO budget studies carried out in the past. In the rural North China Plain, some studies attributed those to soil emissions and more recent studies to dew evaporation. To investigate the contributions of these two processes to HONO temporal variations and unknown production rates in rural areas, HONO and related field observations obtained at the Gucheng Agricultural and Ecological Meteorological Station during spring and autumn were thoroughly analyzed. Morning peaks in HONO frequently occurred simultaneously with those of ammonia (NH3) and water vapor both during spring and autumn, which were mostly caused by dew and guttation water evaporation. In spring, the unknown HONO production rate revealed pronounced afternoon peaks exceeding those in the morning. In autumn, however, the afternoon peak was barely detectable compared to the morning peak. The unknown afternoon HONO production rates were attributed to soil emissions due to their good relationship to soil temperatures, while NH3 soil emissions were not as distinctive as dew emissions. Overall, the relative daytime contribution of dew emissions was higher during autumn, while soil emissions dominated during spring. Nevertheless, dew emission remained the most dominant contributor to morning time HONO emissions in both seasons, thus being responsible for the initiation of daytime OH radical formation and activation of photochemical reactions, while soil emissions further maintained HONO and associated OH radial formation rates at a high level, especially during spring. Future studies need to thoroughly investigate the influencing factors of dew and soil emissions and establish their relationship to HONO emission rates, form reasonable parameterizations for regional and global models, and improve current underestimations in modeled atmospheric oxidation capacity.

Boreal forest ecosystems are regions vulnerable to climate change. Such areas act as the main atmospheric carbon sinks in the world. Wildfires are among the drivers of ecosystem modification and functioning. Boreal wildfires emit an annual average of about 10% of global fire emissions. Taking into account recent climate warming and increases in the frequency of wildfires, boreal forests might switch their functional role from carbon sink to an additional source of atmospheric carbon. Soil respiration is the second largest component of the global carbon cycle and is highly sensitive to disturbance factors, including wildfires. To study the effect of wildfires on soil CO2 emission rates, the fire chronosequence was investigated. During the first few years following the fire, the soil CO2 emission rates were lower compared with the usual levels. It was found that 23 years after a fire, the site demonstrated transition behavior in soil emission rates between disturbed and completely recovered areas. The emission rates at the earliest successional stages are mainly controlled by soil moisture during the summer period. For the other successional stages, soil temperature had a huge impact on soil emission.

Soil respiration (SR) constitutes the largest flux of CO2 from terrestrial ecosystems to the atmosphere. However, there still exist considerable uncertainties as to its actual magnitude, as well as its spatial and interannual variability. Based on a reanalysis and synthesis of 80 site-years for 57 forests, plantations, savannas, shrublands and grasslands from boreal to tropical climates we present evidence that total annual SR is closely related to SR at mean annual soil temperature (SRMAT), irrespective of the type of ecosystem and biome. This is theoretically expected for non water-limited ecosystems within most of the globally occurring range of annual temperature variability and sensitivity (Q10). We further show that for seasonally dry sites where annual precipitation (P) is lower than potential evapotranspiration (PET), annual SR can be predicted from wet season SRMAT corrected for a factor related to P/PET. Our finding indicates that it can be sufficient to measure SRMAT for obtaining a well constrained estimate of its annual total. This should substantially increase our capacity for assessing the spatial distribution of soil CO2emissions across ecosystems, landscapes and regions, and thereby contribute to improving the spatial resolution of a major component of the global carbon cycle.

Atmospheric methyl chloride (CH3Cl) and methyl bromide (CH3Br), compounds involved in the destruction of stratospheric ozone, are simultaneously produced and consumed by the terrestrial biosphere. Here we present a stable isotope incubation technique using13CH3Cl and 13CH3Br as tracers to simultaneously determine production and consumption fluxes in boreal forest soils from Alaska, USA. Measured uptake rates are consistent with previously reported boreal soil results for CH3Br and show a CH3Cl:CH3Br molar consumption ratio of 40:1. Boreal forest soils appear to produce small amounts of these methyl halides as well, but at rates that are negligible in their global budgets. This isotope tracer technique can be applied to laboratory studies of plants and other soils and to field measurements where disturbances to the system can be minimized.

Agricultural soils are the most important anthropogenic source of nitrous oxide to the atmosphere. We observed large shifts with time in the emission rate (from 170 to 16 ng N cm−2 h−1) and in δ15N of N2O emitted (from −46‰ to +5‰ relative to atmospheric N2) from a urea-fertilized and irrigated agricultural field in Mexico. We calculated overall instantaneous enrichment factors for the sampling period, which suggest that the microbial N2O production shifts from nitrification (week 1) to denitrification (week 2). Isotopic signatures of N2O emissions were not always in accord with other proxies (such as NO/N2O emission ratio or water-filled pore space) used to estimate the relative importance of nitrification and denitrification as N2O sources. These observations strongly suggest that the soil surface emissions integrate processes occurring at different depths in the soil and a decoupling of NO and N2O production in this system. Further clues as to the source of N2O come from the positional dependence of 15N in the emitted N2O, reported here for the first time in soil emissions. Enrichment at the central N position increased relative to the terminal N position by 9.3‰ during the first 4 days after irrigation, implying that nitrification preferentially enriches the central N position compared to denitrification. The overall δ15N signature we measured for N2O emitted from N-fertilized agricultural systems is more depleted than observed δ15N values for N2O emitted from more N-limited forest soils. Assuming that one half of the total agricultural N2O emissions associated with the global increase in soil nitrogen fertilizer use have an isotopic composition comparable to those of the agricultural fields reported here, we predict a decline in the isotopic signature of tropospheric N2O during this century of as much as 3‰ for 15N. Although many uncertainties remain, we suggest that measurements of δ15N-N2O in firn air will provide constraints on how the N2O budget has changed during the past century.

We report measurements of the 15N and 18O signature of N2O emitted from tropical rain forest soils at the La Selva Biological station in Costa Rica and in the Fazenda Vitoria in the State of Pará, Brazil. The δ15N values ranged from −34 to 2‰ with respect to atmospheric N2, while δ18O values had a smaller range, from −4 to 18‰ with respect to atmospheric O2. We attribute these large variations to differences in microbial production, consumption, and transport of N2O. In general the δ15N of N2O emissions from an Oxisol soil in Brazil were consistently enriched by ∼20‰ in 15N compared to those from Ultisol and Inceptisol soils in Costa Rica. Denitrification is the most likely source of N2O in both locations during the rainy season, and the 15N of nitrate was similar in both locations. We attribute the overall variability in emitted 15N to differences in the ratio of N2O:N2 escaping from the soil to the atmosphere, with a larger fraction of the N2O reduced to N2 at the Brazilian sites. We found light δ15N-N2O values associated with high N2O emissions in a fertilized agricultural site in Costa Rica and in a “hot spot” of high emissions in the forest site in Brazil. This result suggests that the increase of substrate availability might increase the fractionation associated with N2O production. Overall, the Brazilian Oxisol soils had the most enriched δ15N-N2O emissions yet measured from soils. If these are more representative of tropical soil emissions than the Costa Rica emissions, then the globally averaged δ15N-N2O tropical rain forest soil source is more enriched than previously estimated. The large variations in isotopic signature for N2O emissions demonstrate the potential utility of stable isotopes as tools for understanding the processes of N2O production and consumption in soils.

The impact of natural CO2 emissions in the development of geothermal areas is presently gaining more attention than ever before. In Italian geothermal fields, a reduction in the natural CO2 emissions has been observed. This paper reviews and provides an analysis of the historical production data of boric acid from 1818 to 1867 used to calculate the natural emissions of CO2 associated with boric acid production that pre-dates the use of geothermal resources for power production, which started in 1913. Boric acid was already being extracted from the natural geothermal fluids in geysers and natural ponds emitting steam and gases. After 1827 the ‘lagone coperto’ (covered lake) equipment optimized production, and the drilling of shallow wells (20–30 m) starting in 1836, which further increased the quantity of its extraction. The first geothermal reservoir was developed at the turn of the century and the Larderello geothermal field began to grow. The use of deep wells, keeping pace with the power production, led to the gradual disappearance of the natural ponds and the ‘lagoni’ (lakes) in the historical area, so the residual natural emission of CO2 is presently restricted to diffuse soil emission. Comparisons of the ancient CO2 emissions with those of the Geothermal Power Plant (GPP) in the Larderello area show that both amounts are in the same order of magnitude, suggesting a balance between the depletion of natural emissions and geothermal activity.

Measurements of CO2 flux, soil temperature, and moisture content of selected natural and disturbed soils in central California were made on a monthly basis from August 1994 to October 1995 in an attempt to detect the effects of temperature, moisture, and land use change on CO2 production in soils. Soil CO2 flux displayed a strong negative correlation with soil temperature and a positive correlation with soil moisture at the natural site. However, at the disturbed site, the linear correlation between CO2 flux and temperature/moisture was insignificant. The negative correlation between soil CO2 flux and soil temperature is in contrast to what has been observed in other ecosystems but is typical for Mediterranean ecosystems in which grasses are biologically active only during cool months. Comparison of carbon (C) inventories of paired natural and disturbed soils indicates that both cultivation and logging have resulted in a significant decrease in total soil C content. The reduction in soil C storage is about 26% for the cultivated soil and around 30% for the logged soil. Most of the C loss is from the upper horizons. Radiocarbon (14C) measurements of both recent and archived soil samples demonstrate large differences in C input rate and turnover time between natural and disturbed soils. The average turnover times of organic matter are longer in disturbed soils than in the corresponding natural soils as a result of preferential loss of C from “active” soil C pools. In both natural and disturbed soils, the average turnover times of organic matter increase with depth from decades or less in shallow horizons to hundreds of years or even thousands of years in deeper horizons. Our results show that land use change can have significant impact on soil C cycle and that shallow soil horizons are most susceptible to disturbance because of shorter turnover times of organic C in these horizons.

Biogenic volatile organic compounds (BVOCs) can be released from soils to the atmosphere through microbial decomposition of plant residues or soil organic carbon, root emission, evaporation of litter‐stored BVOCs, and other physical processes. Soils can also act as a sink of BVOCs through biotic and abiotic uptake. Currently, the source and sink capabilities of soils have not been explicitly accounted for in global BVOC estimates from the terrestrial biosphere. In this review, we summarize the current knowledge of soil BVOC processes and aim to propose a generic framework for modelling soil BVOCs based on current understanding and data availability. To achieve this target, we start by reviewing measured sources and sinks of soil BVOCs and summarize commonly reported compounds. Next, we strive to disentangle the drivers for the underlying biotic and abiotic processes. We have ranked the list of compounds, known to be emitted from soils, based on our current understanding of how each process controls emission and uptake. We then present a modelling framework to describe soil BVOC emissions. The proposed framework is an important step toward initializing modelling exercises related to soil BVOC fluxes. Finally, we also provide suggestions for measurements needed to separate individual processes, as well as explore long‐term and large‐scale patterns in soil BVOC fluxes. Plain Language Summary: Living plants emit biogenic volatile organic compounds (BVOCs), which have impacts on regional and global climate. However, BVOCs can also be released from fallen leaf litter, plant roots, and soil organic matter, and some compounds are also consumed by soil microbes. In this article, we begin by sorting out the processes that govern soil emissions and uptakes of BVOCs and summarize the current understanding and available data for each process. Furthermore, we propose a generic modelling framework to add soil BVOC‐related processes into the typical structure existing in many ecosystem models. We also provide suggestions for future measurements that would help with model‐data integration. Key Points: We present biotic and abiotic drivers for soil BVOC emissions and sinksWe summarize the often‐reported compounds and key processes regulating their fluxesWe propose a generic framework for including soil BVOCs in ecosystem models [ABSTRACT FROM AUTHOR]

The Soil Moisture Active Passive (SMAP) satellite mission launched in January 2015 provides worldwide soil moisture (SM) monitoring based on L-band brightness temperature ($T_{B}^{\mathrm{ p}}$) measurements at horizontal ($\text{T}_{B}^{\mathrm{ H}}$) and vertical ($T_{B}^{\mathrm{ V}}$) polarizations. This paper presents a performance assessment of SMAP soil emission model and SM retrieval algorithms for a Tibetan desert ecosystem. It is found that the SMAP emission model largely underestimates the SMAP measured $T_{B}^{\mathrm{ H}}$ (≈ 15 K), and the $T_{B}^{\mathrm{ V}}$ is underestimated during dry-down episodes. A cold bias is noted for the SMAP effective temperature due to underestimation of soil temperature, leading to the $T_{B}^{\mathrm{ p}}$ underestimation (>5 K). The remaining $T_{B}^{\mathrm{ H}}$ underestimation is found to be related to the surface roughness parameterization that underestimates its effect on modulating the $T_{B}^{\mathrm{ p}}$ measurements. Further, the topography and uncertainty of soil information are found to have minor impacts on the $T_{B}^{\mathrm{ p}}$ simulations. The SMAP baseline SM products produced by single-channel algorithm (SCA) using the $T_{B}^{\mathrm{ V}}$ measurements capture the measured SM dynamics well, while an underestimation is noted for the dry-down periods because of $T_{B}^{\mathrm{ V}}$ underestimation. The products based on the SCA with $T_{B}^{\mathrm{ H}}$ measurements underestimate the SM due to underestimation of $T_{B}^{\mathrm{ H}}$ , and the dual-channel algorithm overestimates the SM. After implementing a new surface roughness parameterization and improving the soil temperature and texture information, the deficiencies noted above in $T_{B}^{\mathrm{ p}}$ simulation and SM retrieval are greatly resolved. This indicates that the SMAP SM retrievals can be enhanced by improving both surface roughness and adopted soil temperature and texture information for Tibetan desert ecosystem. [ABSTRACT FROM AUTHOR]

Soil is heated or burned during field biomass burning, including forest fires, grassland fires, and open straw burning. The characteristics of the aerosols released from the high-temperature heated soil have not been reported, according to our knowledge. In this work, three types of soil were heated at different temperatures in a tubular furnace to mimic the heating process during field burning. The particulate emission factors (EF PM), particle size distributions, organic carbon (OC) contents, and organic compositions of the emitted aerosols were investigated in detail. It was found that the particulate matter (PM) produced by soil at high temperature (≥300 °C) cannot be neglected. The PM emission flux of the shallow surface of soil (with depth less than 5 cm) could be dozens of times higher than those from biomass burning when the surface temperature rises to 500 °C. The soil heated at higher temperatures emitted more particles with smaller sizes. These aerosols also contain toxic and harmful substances such as aromatics, heterocycles and nitriles. Therefore, the results strongly suggest that aerosol emissions from the heated soil during the field biomass burning cannot be ignored and could have significant environmental impacts. [Display omitted] • Amounts of aerosol particles were emitted from the high-temperature heated soil. • PM emission factors and OC contents were higher for the soil heated at ≥ 300 °C. • PM emission flux for the heated soil was near or higher than the biomass burning. • The soil-emitted PM were smaller with the increasing heating temperature and time. • Soil thermal-volatility and pyrolysis contribute to the field burning aerosol emission. [ABSTRACT FROM AUTHOR]

Hydroelectric generation is important in many countries. In Brazil, it accounts for over 70% of this generation. Despite a renewable energy source, there is great concern about potential emissions of greenhouse gases produced by the hydropower reservoirs. Pre-existing reservoirs creation, the greenhouse gas measurements should considered to calculating the net contribution of each project. Net greenhouse gas (GHG) emissions from hydropower reservoirs has been defined as the differences between balances of GHG emissions and removals during post- and pre-impoundment regimes of mass transport and storage in the affected area Due to the expansion of this type of energy to Brazil׳s Amazon region, this study was developed to evaluate emissions of pre-existing terrestrial areas of the future Belo Monte located in the Amazon region. Four campaigns were carried out over a period of one year, fifteen areas sampled in each campaign, scattered in areas with vegetation of forest and grassland. The carbon dioxide fluxes (CO 2 ), methane (CH 4 ) and nitrous oxide (N 2 O) of soils were measured. The median values of CH 4 emissions were 9.97±3.55 mg CH 4 m −2 d −1 and 11.34±1.62 mg CH 4 m −2 d −1 for pasture and forest, respectively. For CO 2 in the pasture was 10448.41±3036.48 mg CO 2 m −2 d −1 and 8004.50±1314.98 mg CO 2 m −2 d −1 for forest. The median fluxes for N 2 O were near zero, and 0.78±0.56 mg N 2 O m −2 d −1 for pasture and 0.67±0.29 mg N 2 O m −2 d −1 for forest. The study showed that the terrestrial areas previous reservoir creation act as potential emitter of greenhouse gases. [ABSTRACT FROM AUTHOR]

This work is a synthesis of a 5-year estimation of nitrogen balance at a semi-arid, semi-natural, undisturbed grassland site (Bugac). We measured the N input of atmospheric pollutants by wet and dry deposition of gases and aerosols, while we considered N output as NO and NO gases volatilized from soil. Besides measurements of soil fluxes, the denitrification-decomposition (DNDC) ecological model was also used and simulations were compared to and validated against the measured values. The daily flux simulations generally did not match well the measured data for NO and NO. In most cases, the mean fluxes were underestimated, though results of the comparison of monthly values suggest that model data, together with observed deposition data, are applicable to estimate the net N balance for grasslands. The calculated yearly N balance (net flux) between atmosphere and surface, without biological fixation and effect of grazing, ranged between −9.4 and −14 kg N ha year as the sum of the measured deposition and emission terms, −11 to −15 and 0.9 to 2.9 kg N ha year, respectively, between 2006 and 2010. Observed and modeled soil emissions were lower by one order of magnitude than atmospheric deposition. Considering the biological nitrogen fixation and the effect of grazing (effects of both grazed plant and excreta), the net nitrogen balance varies within −6.6 and −11 kg N ha year. It seems - taking into account the high uncertainty in calculation due to the effect of grazing - that sources of nitrogen exceed the sinks; the surplus is probably mineralized in the soil. [ABSTRACT FROM AUTHOR]

Kazakhstan Western ecosystems are intensively used in agricultural production. Assessing greenhouse gas emissions from soils, especially CO2, is important. In the upper stages, microbiology, characteristics and condition of the soil change. Biological intensity indicators are soil respiration processes, numerous microbiocenoses species composition. Soil CO2 emissions were measured 5 times monthly during three years. The CO2 flow rate from soil surface is measured by a closed dynamic chamber method with Li-8100A field respirometer. Metagenomic soil testing used bacteria DNA, archaea, real-time PCR, 16SrRNA sequencing. The soil CO2 monthly dynamics fluxes varied among the lands, within the season. In 2020, the CO2 emissions soil peak noted in the pasture. There is a slight decline in summer with a decrease towards the cold season. Comparison between the CO2 flux pasture soils is less in virgin soil. The minimum CO2 flux was recorded in November - February; in the spring, the flux increases. The above CO2 emissions were recorded in summer. In soils, there is wide variety of microorganisms with opposite and incompatible properties for one habitat. The microbial communities structure identified at the family level. The taxonomic samples structure ominated by phylae - Actinobacteria, Proteobacteria, Chloroflexi, Acidobacteria, Gemmatimonadetes, Firmicutes, Actinobacteria. The spread explained by increased actinomycetes resistance characteristic to low moisture content with long dry period. For comparative evaluation microbial communities results comparing by cenoses of upper horizons with dark chestnut soil indicators. This violation caused microorganisms resistance to disturbing factors. On anthropogenically disturbed saline soils, the bacteria found were specific and resistant to critical conditions. CO2 emission in soil varied cenosis type. The CO2 intensity factors were precipitation deficit, high temperature. The profile microorganisms distribution corresponded to the soil horizons humus content. During summer soil drying, the deep soil horizons abundance occurred where moisture is retained. [ABSTRACT FROM AUTHOR]

The variability of atmospheric ammonia (NH 3 ) in downtown Toronto was investigated through the analysis of 24 hr integrated denuder NH 3 samples collected at a site above a street canyon every third day from July 2003 to September 2011 (Dataset 1). The measured NH 3 mixing ratios ranged from below the detection limit to 14.7 ppb during the eight-year period. Distinctive seasonal variations were observed with summer averages (±standard deviation) of 3.9 ± 1.6 ppb and winter averages of 1.1 ± 0.6 ppb. Two other datasets, weekly/biweekly passive samples of NH 3 monitored at 74 agricultural and remote sites across southern Ontario during the period of June 2006 to March 2007 (Dataset 2) and semi-continuous measurements of NH 3 and ammonium (pNH 4 + ) in PM 2.5 collected at a site inside a street canyon approximately 170 m away from the downtown site in December 2008 and February, March and May 2009 (Dataset 3), were further used to evaluate the potential NH 3 sources in downtown Toronto. The NH 3 mixing ratios at the downtown location were higher than those at the surrounding agricultural sites, and the mixing ratios within the street canyon were almost double those measured above it. These results suggested that the observed NH 3 at the downtown location was mainly from local sources within the street canyon. Analysis of Dataset 3 showed that the diurnal cycles of NH 3 at the downtown location cannot be simply explained by traffic and water consumption patterns. A green space inside the street canyon was identified as a potential important source contributing to the observed NH 3 when T > 0 °C. However, the major NH 3 emission sources at T ≤ 0 °C are yet to be investigated. [ABSTRACT FROM AUTHOR]

The atmospheric nitrogen cycle is a key process driving the earth's environmental evolution. Current model studies require knowledge of NO x soil emissions from various land types, but desert emissions remain unquantified or are not addressed with high confidence. Our measurements at two observatories in Taklimakan desert during a dust episode showed an approximately stable and dust-independent nitrate in the air. Its concentration estimated from PM2.5, PM10 and TSP samples under non-dust, floating dust and dust storm conditions was 3.81 ± 1.24 μg m−3, 2.95 ± 0.69 μg m−3, 4.99 ± 1.71 μg m−3, respectively, despite the more-than-one-order difference of dust loading. This concentration was much larger than that in remote marine and tropical forest air. Comprehensive investigation revealed a similar presence of nitrate in other desert air. The nitrate was hypothesized to be the consequence of the conversion of NO x released from desert soils. These results indicate a background-like nitrate and active reactions of nitrogen compounds in desert air. [ABSTRACT FROM AUTHOR]

Abstract: Decomposition processes are extremely important in biological soil crusts (BSCs). Although the effects of temperature and moisture on such processes have been widely studied, little is known about the influence of the readily metabolizable substrate (labile C) and how this substrate varies in different types of BSCs. In the present study, BSCs formed by cyanobacteria (CYANO) and by lichens (DIPLOS and LEPRA) were incubated at 25 °C (optimum temperature) and different moisture levels, for evaluation of the pool of labile C in the crust layers. Labile C was estimated as the sum of CO2–C emitted and the C extracted with hot water (80 °C) at the end of the incubation period. In all crusts, the relationship between emission and moisture fitted a quadratic model. For the different moisture contents, the sum of CO2–C emitted and C extracted with hot water converged to a constant value for each type of crust. This value, considered as the maximum content of labile C in the crust, was extremely high in DIPLOS, reaching up to 40% of the total organic C (TOC) initially present. In all crusts, and independently of the consumption of labile C, simple sugars (sucrose, glucose) remained at the end of the incubation period, which suggests that these sugars may play a protective role in BSCs. The presence of mannitol suggests that the fructose released during hydrolysis of sucrose was reduced to mannitol, thus enabling electron transport during moments of intense respiratory stress. The intense respiration in DIPLOS is partly due to the metabolism of polyphenols, which are possibly derived from the growth and death of free-living fungi that proliferate during incubation of the crusts. These results demonstrate that the metabolic processes in BSCs differ depending on the type of organisms that form the crusts and that there is a high risk of C loss from Diploschistes BSCs after heavy rainfall events. [Copyright &y& Elsevier]

This study reports on the utilization of microwave modeling, together with ground truth, and L-band (1.4-GHz) brightness temperatures to investigate the passive microwave characteristics of a conifer forest floor. The microwave data were acquired over a natural Virginia Pine forest in Maryland by a ground-based microwave active/passive instrument system in 2008/2009. Ground measurements of the tree biophysical parameters and forest floor characteristics were obtained during the field campaign. The test site consisted of medium-sized evergreen conifers with an average height of 12 m and average diameters at breast height of 12.6 cm. The site is a typical pine forest site in that there is a surface layer of loose debris/needles and an organic transition layer above the mineral soil. In an effort to characterize and model the impact of the surface litter layer, an experiment was conducted on a day with wet soil conditions, which involved removal of the surface litter layer from one half of the test site while keeping the other half undisturbed. The observations showed detectable decrease in emissivity for both polarizations after the surface litter layer was removed. A first-order radiative transfer model of the forest stands including the multilayer nature of the forest floor in conjunction with the ground truth data are used to compute forest emission. The model calculations reproduced the major features of the experimental data over the entire duration, which included the effects of surface litter and ground moisture content on overall emission. Both theory and experimental results confirm that the litter layer increases the observed canopy brightness temperature and obscure the soil emission. [ABSTRACT FROM AUTHOR]

Abstract: Quantifying the nitrous oxide (N2O) and nitric oxide (NO) fluxes emitted from croplands remains a major challenge. Field measurements in different climates, soil and agricultural conditions are still scarce and emissions are generally assessed from a small number of measurements. In this study, we report continuously measured N2O and NO fluxes with a high temporal resolution over a 2-year crop sequence of barley and maize in northern France. Measurements were carried out using 6 automatic chambers at a rate of 16 mean flux measurements per day. Additional laboratory measurements on soil cores were conducted to study the response of NO and N2O emissions to environmental conditions. The detection limit of the chamber setup was found to be 3ngNm−2 s−1 for N2O and 0.1ngNm−2 s−1 for NO. Nitrous oxide fluxes were higher than the threshold 37% of the time, while they were 72% of the time for NO fluxes. The cumulated annual NO and N2O emissions were 1.7kgN2O-Nha−1 and 0.5kgNO-Nha−1 in 2007, but 2.9kgN2O-Nha−1 and 0.7kgNO-Nha−1 in 2008. These inter-annual differences were largely related to crop types and to their respective management practices. The forms, amounts and timing of nitrogen applications and the mineralization of organic matter by incorporation of crop residues were found to be the main factor controlling the emissions peaks. The inter-annual variability was also due to different weather conditions encountered in 2007 and 2008. In 2007, the fractioned N inputs applied on barley (54kgha−1 in March and in April) did not generate N2O emissions peaks because of the low rainfall during the spring. However, the significant rainfall observed in the summer and fall of 2007, promoted rapid decomposition of barley residues which caused high levels of N2O emissions. In 2008, the application of dairy cattle slurry and mineral fertilizer before the emergence of maize (107kgNmin ha−1 or 130kgNtot ha−1 in all) coincided with large rainfalls promoting both NO and N2O emissions, which remained high until early summer. Laboratory measurements corroborated the field observations: NO fluxes were maximum at a water-filled pore space (WFPS) of around 27% while N2O fluxes were optimal at 68% WFPS, with a maximum potentially 14 times larger than for NO. [Copyright &y& Elsevier]

Abstract: Nitrous oxide (N2O) is emitted into the atmosphere in substantial quantities as an intermediate product of mainly denitrification processes and soil nitrification. N2O emission from Hungarian sandy and loess type soils has been measured between August 2002 and December 2004. The effects of soil parameters and different farming activities (grazing exclusion, irrigation and mineral fertilization) on the rate of emission were investigated. Soil N2O efflux was determined by measuring the accumulation of N2O in 10 parallel small (V =400cm3, A =80cm2) static chambers. Samples were taken with evacuated tubes followed by gas chromatography–mass spectrometry analysis. Emission from sandy grassland under extensive farming proved to be negligible below soil temperature of 5°C, the mean fluxes at t soil >10°C and t soil <10°C were differing significantly (15.4 and 1.7μgNm−2 h−1, respectively). N2O efflux was linked to temperatures up to t soil =20°C, while at higher soil temperatures a decrease of efflux was observed. The optimum soil wetness (WFPS, water-filled pore space) for N2O production was between 40 and 50% for this sandy soil. The annual sum of efflux for control plots in dry (2003) and wet (2004) years was almost the same (0.80 and 0.74kgNha−1 yr−1, respectively), probably due to the fact that in dry year soil wetness is lower than the optimum, and vice versa, in a wet year the high WFPS did not favoured N2O production. Grazing (50–80 cows per km2) enhanced emission by 4–18% in dry and wet years, respectively. Around 6% of total atmospheric deposition (13.8kgNha−1 yr−1) was transformed into N2O and emitted into the atmosphere from the sandy soil. A two-year fertilization experiment above loess soil (August 2002–July 2004, with regular precipitation amount during the period) resulted in an emission factor of 0.26% as a consequence of applying 100kgNha−1 yr−1 ammonium nitrate mineral fertilizer in April, each year. Average fluxes were 1.13 and 0.90kgNha−1 yr−1 above fertilized and control plots, respectively. Monoliths from loess soil were used to study the effect of irrigation on N2O fluxes. In contrast to sandy soil there were detectable soil fluxes below 5°C. N2O production increases with soil temperature until 15–20°C above which lower emissions were detected. The optimum wetness for N2O production in loess soil was around 30–40 WFPS but above 70–80% (up to saturation) other, yet unexplained maximum was observed. Irrigation enhanced the soil flux by 70% in the dry year (2003), when measured fluxes were 1.56 and 0.92kgNha−1 yr−1 on irrigated and control plots, respectively. [Copyright &y& Elsevier]

Abstract: The emission of CO2 from Galician (NW Spain) forest, grassland and cropped soils was studied in a laboratory experiment, at different temperatures (10–35 °C) and at moisture contents of 100% and 160% of the field capacity (FC) of each soil (the latter value corresponds to saturated conditions, and represents between 120% and 140% of the water holding capacity, depending on the soil). In the forest soil, respiration in the flooded samples at all temperatures was lower than that at 100% field capacity. In the agricultural (grassland and cropped) soils the emission was higher (particularly at the highest incubation temperatures) in the soils wetted to 160% of the field capacity than in those wetted to 100% of the field capacity. In all cases the emission followed first order kinetics and the mineralization constants increased exponentially with temperature. In the forest soil, the Q 10 values were almost the same in the soils incubated at the two moisture contents. The grassland and cropped soils displayed different responses, as the Q 10 values were higher in the soils at 160% than in those at 100% of field capacity. In addition, and particularly at the highest temperatures, the rate of respiration increased sharply 9 and 17 days after the start of the incubation in the grassland and in the cropped soil, respectively. The above-mentioned anomalous response of the grassland and cropped soils under flooding conditions may be related to the agricultural use of the soils and possibly to the intense use of organic fertilizers in these soils (more than 150 kg N ha−1 year−1 added as cattle slurry or manure, respectively, in the grassland and cropped soils). The observed increase in respiration may either be related to the development of thermophilic facultative anaerobic microbes or to the formation during the incubation period of a readily metabolizable substrate, possibly originating from the remains of organic fertilizers, made accessible by physicochemical processes that occurred during incubation under conditions of high moisture. [Copyright &y& Elsevier]

Soils are a significant source for atmospheric NO. However, due to the limited number of measurements and in view of the high temporal and spatial variability of NO emissions, as originating from dependencies from a series of environmental constraints such as soil properties, meteorology or N fertilization, inventories of soil NO emissions are still highly uncertain. In this work, the agricultural DNDC model was modified and applied on site scale in order to evaluate its capability to simulate soil NO emissions. DNDC captured differences in the magnitude of NO emissions between sites, but was less successful when simulating observed day-by-day variations. However, major peak emission events, e.g. due to fertilizer application or following rainfall events, were mostly simulated. DNDC as well as its forest version Forest-DNDC were finally linked to a GIS to calculate NO emissions from agricultural and forest soils across Europe. Using the same databases for agricultural soils, we also compared our estimate with other commonly used methodologies (Skiba-EMEP/CORINAIR, Yienger and Levy, Stehfest and Bouwman). A canopy reduction factor was not applied in this study. Estimates for NO emissions for agricultural soils for EU15 states varied in a range of 48.9–189.8kt NO-N for the year 2000 depending on the approach used (Yienger and Levy > DNDC > Stehfest and Bouwman > Skiba-EMEP/CORINAIR). For forests, using the model Forest-DNDC as the only approach, we calculated soil NO emissions to be 75.1kt NO-Nyr−1. The results show that soils in EU15 states are significant sources of atmospheric NO, though the share of soil NO emissions on total NO x emissions (incl. NO x emissions by combustion processes) in EU15 was only 4–6%. Given that soil NO emissions are largely driven by the availability of inorganic nitrogen (fertilization) and temperature, emissions are larger during the vegetation period. Especially during early summer when fertilizer-induced NO emissions from agricultural soils are peaking, the contribution of soil emissions to total NO x emissions may most likely be well above 10%. [Copyright &y& Elsevier]

Nitrogen isotopic signatures are very useful for identifying sources of atmospheric NO x or NO3 −. Although soil is a major source of atmospheric nitric oxide (NO), yet nitrogen isotopic composition of soil-released NO has not been directly measured. Since a large portion of soil NO emission is induced by fertilizer application in food production, in the present study we determined N isotopic signatures of NO from cropland soils fertilized with urea and ammonium bicarbonate (ABC). NO was oxidized to NO2 and then converted to nitrite for nitrogen isotope analysis; tests with NO standard gas revealed no significant nitrogen isotopic fractioning during the trapping and processing procedures. While the applied urea and ABC had δ 15N values of +1.3‰ and +7.2‰, respectively, soil-released NO had δ 15N values increasing from −48.9‰ (day 2) to −28.0‰ (day 13) after urea fertilization and from −48.6‰ (day 2) to −19.9‰ (day 13) after ABC fertilization. This much 15N depleted isotopic composition of soil-released NO makes it possible to distinguish soil emission from fuel combustion for the contribution of atmospheric NO x or NO3 −. Nitrogen isotopic compositions of soil substrate NH4 + and NO3 − were also determined, and the instantaneous nitrogen isotopic enrichment factor of NO relative to those of substrate NH4 + and NO3 − indicated both nitrification and denitrification occurred for NO production, although only NH4 +-based fertilizers were applied. [Copyright &y& Elsevier]

El Niño–La Niña cycles strongly influence dry and wet seasons in the tropics and consequently nitrous oxide (N2O) emissions from tropical rainforest soils. We monitored whole-system and soil chamber N2O fluxes during 5-month-long droughts in the Biosphere 2 tropical forest to determine how rainfall changes N2O production. A consistent pattern of N2O flux changes during drought and subsequent wetting emerged from our experiments. Soil surface drying during the first days of drought, presumably increased gas transport out of the soil, which increased N2O fluxes. Subsequent drying caused an exponential decrease in whole-system (4.0±0.1% day−1) and soil chamber N2O flux (8.9±0.8% day−1; south chamber; and 13.7±1.1% day−1; north chamber), which was highly correlated with soil moisture content. Soil air N2O concentration ([N2O]) and flux measurements revealed that surface N2O production persisted during drought. The first rainfall after drought triggered a N2O pulse, which amounted to 25% of drought-associated reduction in N2O flux and 1.3±0.4% of annual N2O emissions. Physical displacement of soil air by water and soil chemistry changes during drought could not account for the observed N2O pulse. We contend that osmotic stress on the microbial biomass must have supplied the N source for pulse N2O, which was produced at the litter–soil interface. After the pulse, N2O fluxes were consistently 90% of predrought values. Nitrate change rate, nutrient, [N2O], and flux analyses suggested that nitrifiers dominated N2O production during the pulse and denitrifiers during wet conditions. N2O flux measurements in Biosphere 2, especially during the N2O pulse, demonstrate that large-scale integration methods, such as flux towers, are essential for improving ecosystem N2O flux estimates. [ABSTRACT FROM AUTHOR]

Soils have been widely acknowledged as important natural sources of nitric oxide (NO) and meanwhile sinks of nitric dioxide (NO 2). High nitrogen deposition across South China could potentially result in large NO emissions from subtropical forests soils there. In this study, the dynamic chamber method was applied to monitor NO and NO 2 fluxes at two subtropical forest sites in South China, namely "Qianyanzhou" (QYZ) and "Tieshanping" (TSP). Chronically higher N deposition occurred at TSP than that at QYZ. Besides soil water filled pore spaces (WFPS) and temperature, ambient NO concentration could also possibly be important in regulating temporal NO emissions, especially in the winter. For both sites, the optimum soil temperature was above 25 °C, while the optimum WFPS for NO release at QYZ was higher (65–70%) than that at TSP (<23%). Moreover, heavy rainfall could trigger NO emission pulses from moist soils at QYZ, while rainfall-induced NO pulses were only observed after a long drying period at TSP. Distinctly different contents of mineral nitrogen and soil moisture conditions between the two sites might induce the divergent preference of WFPS and responses to rainfall. The cumulative soil emission of NO reached 0.41 ± 0.01 and 0.76 ± 0.01 kg N ha−1 yr−1 at QYZ and TSP, contributing to 2.5% and 1.4% of the annual throughfall N input, respectively. At both sites, NO 2 were mainly deposited to soils, accounting for 2% and 21% of soil-emitted NO at QYZ and TSP, respectively. The observed annual NO emissions at these two sites were larger than the median values observed for tropical and temperate forests and unfertilized croplands. Higher N deposition could induce larger NO emission potential, while soil temperature and pH might also be important in regulating regional soil NO emissions as N-loss from subtropical forests. [Display omitted] • Soil NO emissions were 0.41 and 0.76 kg N ha−1 yr−1 at two subtropical forests. • NO 2 fluxes were bi-directional above subtropical forest soils. • Ambient NO concentration contributed to regulating variability of soil NO emissions. • N deposition induce larger potentials of soil NO emissions. [ABSTRACT FROM AUTHOR]

Soils have been widely acknowledged as important natural sources of nitric oxide (NO) and meanwhile sinks of nitric dioxide (NO 2 ). High nitrogen deposition across South China could potentially result in large NO emissions from subtropical forests soils there. In this study, the dynamic chamber method was applied to monitor NO and NO 2 fluxes at two subtropical forest sites in South China, namely "Qianyanzhou" (QYZ) and "Tieshanping" (TSP). Chronically higher N deposition occurred at TSP than that at QYZ. Besides soil water filled pore spaces (WFPS) and temperature, ambient NO concentration could also possibly be important in regulating temporal NO emissions, especially in the winter. For both sites, the optimum soil temperature was above 25 °C, while the optimum WFPS for NO release at QYZ was higher (65-70%) than that at TSP (<23%). Moreover, heavy rainfall could trigger NO emission pulses from moist soils at QYZ, while rainfall-induced NO pulses were only observed after a long drying period at TSP. Distinctly different contents of mineral nitrogen and soil moisture conditions between the two sites might induce the divergent preference of WFPS and responses to rainfall. The cumulative soil emission of NO reached 0.41 ± 0.01 and 0.76 ± 0.01 kg N ha -1 yr -1 at QYZ and TSP, contributing to 2.5% and 1.4% of the annual throughfall N input, respectively. At both sites, NO 2 were mainly deposited to soils, accounting for 2% and 21% of soil-emitted NO at QYZ and TSP, respectively. The observed annual NO emissions at these two sites were larger than the median values observed for tropical and temperate forests and unfertilized croplands. Higher N deposition could induce larger NO emission potential, while soil temperature and pH might also be important in regulating regional soil NO emissions as N-loss from subtropical forests., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

The impact of natural CO2 emissions in the development of geothermal areas is presently gaining more attention than ever before. In Italian geothermal fields, a reduction in the natural CO2 emissions has been observed. This paper reviews and provides an analysis of the historical production data of boric acid from 1818 to 1867 used to calculate the natural emissions of CO2 associated with boric acid production that pre-dates the use of geothermal resources for power production, which started in 1913. Boric acid was already being extracted from the natural geothermal fluids in geysers and natural ponds emitting steam and gases. After 1827 the 'lagone coperto' (covered lake) equipment optimized production, and the drilling of shallow wells (20–30 m) starting in 1836, which further increased the quantity of its extraction. The first geothermal reservoir was developed at the turn of the century and the Larderello geothermal field began to grow. The use of deep wells, keeping pace with the power production, led to the gradual disappearance of the natural ponds and the 'lagoni' (lakes) in the historical area, so the residual natural emission of CO2 is presently restricted to diffuse soil emission. Comparisons of the ancient CO2 emissions with those of the Geothermal Power Plant (GPP) in the Larderello area show that both amounts are in the same order of magnitude, suggesting a balance between the depletion of natural emissions and geothermal activity. [ABSTRACT FROM AUTHOR]

Uncertainties exist in the current estimates of atmospheric dry deposition and air-surface exchange of atmospheric mercury in chemical transport models and monitoring networks. To quantitatively assess these uncertainties, two bidirectional air-surface exchange models for gaseous elemental mercury (Hg0), originally developed by Wang et al. (2014, Atmos. Chem. Phys., doi:10.5194/acp-14-6273-2014) and Wright and Zhang (2015, J. Adv. Model. Earth Syst., doi:10.1002/2014MS000367), were compared quantitatively. The two models were applied to two vegetated land covers, including a deciduous broadleaf forest and a cropland, near a monitoring site in Georgia, USA for calculating air-surface exchange fluxes of Hg0. The model inputs include measured 2-hourly ambient Hg0 concentrations and archived surface meteorology data produced from a weather forecast model. The estimated annual net fluxes differed significantly between the two models, i.e., −0.7 μg m−2yr−1 by Wang et al.'s model vs. −8.6 μg m−2yr−1 by Wright & Zhang's model over the deciduous broadleaf forest and 8.4 μg m−2yr−1 vs. −10.7 μg m−2yr−1 over the cropland. When considering dry deposition and emission fluxes separately, similar deposition fluxes were produced by the two models, regardless of season and land cover, due to the similar canopy resistance formulas used in the two models. Much higher soil and lower stomatal emission fluxes were produced by Wang et al.'s model than Wright & Zhang's model (soil: 30 vs. 8.9 μg m−2yr−1 and stomata: 0.5 vs. 8.3 μg m−2yr−1, averaged over the two canopies) due to the very different emission potentials used in the two models. Cuticle emission fluxes contributed less than 0.1% to the total emission flux in Wang et al.'s model, and were not considered in Wright & Zhang's model. The differences in soil emission flux, total emission flux, and net flux were more pronounced in winter than in the other seasons. The large differences in the net fluxes between the two models were primarily caused by their very different schemes of soil emission potential. • Compared two bidirectional air-surface exchange models of gaseous elemental mercury. • Annual & seasonal net exchange fluxes differed significantly between the two models. • Separating deposition & emission fluxes allows analyzing reasons of differed fluxes. • Large differences in emissions due to different schemes of soil emission potential. • Different stomatal emission potentials also led to discrepancies in emissions. [ABSTRACT FROM AUTHOR]