Vertical Concentration Distribution Research Articles

Dynamics in C, N, and P stoichiometry and microbial biomass following soil depth and vegetation types in low mountain and hill region of China

Changes in soil carbon (C):nitrogen (N):phosphorus (P) stoichiometry have great significance on understand regulatory mechanism and restoration of ecosystem functions. However, the responses of C, N and P stoichiometry to soil depth and different vegetation types remains elusive. To address this problem, the study aims to explore the effects of soil depth and vegetation types on soil C, N, and P stoichiometry, and their relationships with microbial biomass in low mountain and hill region of China. The results indicated that soil SOC and TN concentrations in oak forest were markedly higher than those in grassland, and the vertical distribution of SOC and TN concentration showed an inverted triangle trend as the soil deepens. However, there was no significant change in soil TP concentration among 0–20 cm, 20–40 cm, and 40–60 cm. Soil C/N among different layers (0–20, 20–40, and 40–60 cm) is narrower fluctuation margin, and its value is basically stable within a certain range (11–14.5). Both soil C/P and N/P showed significant variability in different vegetation types, and soil N/P decreased with soil layers deepen. Both the microbial biomass C (MBC) and N (MBN) showed a decreasing trend with the increase of soil depth, and three soil layers from high to low was: oak forest > pine forest > grassland. Our results will potentially provide useful information for the vegetation restoration and forest management and great significance to enrich the scientific theory of ecological stoichiometry.

Structure of the Field of the Colored Dissolved Organic Matter Concentration in the Kerch Strait

Purpose. Using the data obtained in the expeditions, 2001–2014, the authors intend to identify the typical features of vertical structure of the colored dissolved organic matter (fDOM) concentration field in the Kerch Strait, to type the fDOM(z) profiles, to zone the region under consideration according to a given set of the qualitative features, and also to determine the features of statistical characteristics of the fDOM concentration distribution on the sea surface layer for the water areas with a typical structure. Methods and Results. The typing was carried out by the method of visual expert assessment of the curves of vertical distribution of concentration of the considered value. It was based on analyzing the fDOM(z) profile shapes. To reveal the boundaries of the areas with typical stratification of the fDOM content field, the thermohaline field structure was analyzed. Three types of water vertical structure were identified; they differed in the fDOM(z) profile shape and in statistical indices of empirical distribution of this substance concentration on the sea surface. These are the Azov Sea and the Black Sea types peculiar to the Azov and Black seas waters not contaminated by dissolved organic matter, and the type, the structure of which identifies the waters containing the anthropogenic component in the concentration field of the analyzed value. The latter type is characterized by a special intrusive shape of the fDOM(z) profile. For each of the identified stratification types, the histograms of the fDOM concentration distribution on the sea surface were calculated. Conclusions. The fDOM(z) profiles were typed. The Kerch Strait water area was zoned in accordance with a given set of the preliminary revealed qualitative features. The boundaries of the areas with typical stratification and their displacements were determined. It is shown that each structure type has its own statistical distribution of concentration of the considered value on the sea surface

Struktura polya kontsentratsii okrashennogo rastvorennogo organicheskogo veshchestva v Kerchenskom prolive

Purpose. Using the data obtained in the expeditions, 2001–2014, the authors intend to identify the typical features of vertical structure of the colored dissolved organic matter (fDOM) concentration field in the Kerch Strait, to type the fDOM(z) profiles, to zone the region under consideration according to a given set of the qualitative features, and also to determine the features of statistical characteristics of the fDOM concentration distribution on the sea surface layer for the water areas with a typical structure. Methods and Results. The typing was carried out by the method of visual expert assessment of the curves of vertical distribution of concentration of the considered value. It was based on analyzing the fDOM(z) profile shapes. To reveal the boundaries of the areas with typical stratification of the fDOM content field, the thermohaline field structure was analyzed. Three types of water vertical structure were identified; they differed in the fDOM(z) profile shape and in statistical indices of empirical distribution of this substance concentration on the sea surface. These are the Azov Sea and the Black Sea types peculiar to the Azov and Black seas waters not contaminated by dissolved organic matter, and the type, the structure of which identifies the waters containing the anthropogenic component in the concentration field of the analyzed value. The latter type is characterized by a special intrusive shape of the fDOM(z) profile. For each of the identified stratification types, the histograms of the fDOM concentration distribution on the sea surface were calculated. Conclusions. The fDOM(z) profiles were typed. The Kerch Strait water area was zoned in accordance with a given set of the preliminary revealed qualitative features. The boundaries of the areas with typical stratification and their displacements were determined. It is shown that each structure type has its own statistical distribution of concentration of the considered value on the sea surface.

Large scale mapping of soil organic carbon concentration with 3D machine learning and satellite observations

Canada has extensive forests and peatlands that play key roles in global carbon cycle. Canadian soils and peatlands are assumed to store approximately 20% of the world’s soil carbon stock. However, the spatial and vertical distributions of the soil organic carbon (SOC) concentration in Canada have not been systematically investigated. SOC concentration, expressed in g C kg−1 soil, affects the chemical and physical properties of the soil, such as water infiltration ability, moisture holding capacity, nutrient availability, and the biological activity of microorganisms. In this study, we tested a three dimensional (3D) machine learning approach and 40 spatial predictors derived from 20 years of optical and microwave satellite observations to estimate the spatial and vertical distributions of SOC concentration in Canada in six depth intervals up to 1 m. A quantile regression forest method was used to build an uncertainty map showing 80% of prediction intervals. Results showed that a random forest model associated with 25 covariates was successful in capturing 83% of spatial and vertical SOC variation over the country. Soil depth was the most important covariate to predict SOC concentration, followed by surface temperature and elevation. The SOC concentration in forested areas was highest in the top layers (0–5 cm), but soils located in peatlands showed higher C concentration in all soil depths. Among the terrestrial ecozones of Canada, Pacific Maritime and the Hudson Plain mostly covered by forest trees and peatlands, respectively, show highest SOC concentration, while the lowest concentration are observed in the Prairies and Mixed Wood Plain ecosystems that are the agricultural areas of the country. This study provides a deeper understanding of the major factors controlling SOC concentration in Canada and shows potential areas with high carbon reserves, which are crucial in view of the ongoing climate change. In addition, the presented methodological framework has great potential to be used in future soil carbon storage inventories using satellite observations. Mapping SOC concentration and associated uncertainties in Canada are fundamental to detect trends of gains or losses in SOC linked to recent and future national or global policy decisions related to soil quality and carbon sequestration.

Variation of Isoprenoid GDGTs in the Stratified Marine Water Column: Implications for GDGT-Based TEX86 Paleothermometry

Isoprenoid glycerol dialkyl glycerol tetraethers (isoGDGTs) derived from archaea are lipid biomarkers that exhibit high sensitivity to changes in water temperature, leading to the widespread application of the isoGDGT-based tetraether index of 86 carbon atoms (TEX86) in surface seawater temperature (SST) reconstruction. However, there remain some uncertainties regarding the robustness of TEX86 under changing water conditions (e.g., variations in water depth, oxygen and pH). Here, we analyzed isoGDGTs in suspended particles at different depths of the East China Sea (ECS) during summer 2020, aiming to constrain the applicability of the TEX86 proxy in coastal waters. Our data showed that the isoGDGTs were mainly derived from planktonic Thaumarchaeota, as revealed by the low ratio of GDGT-0/crenarchaeol (<0.5). The vertical distribution of isoGDGT concentration depicted a downward increase from the surface to the bottom. This observation was likely shaped by Thaumarchaeota, which regulate the extent of ammonia oxidation based on the availability of ammonium. The occurrence of maximal isoGDGT concentrations in the bottom layer suggests that the isoGDGTs in sediments are mainly controlled by bottom archaeal production rather than surface archaeal production. By reanalyzing the published isoGDGT data of surface sediments in the ECS inner shelf, we found that the sedimentary TEX86 relates much better to the annual mean bottom seawater temperature (BST) than to the annual mean SST, indicating that sedimentary TEX86 is more inclined to be a proxy for the BST in the shallow ECS. In addition, the positive bias of TEX86 driven by low dissolved oxygen and low pH was observed under the pycnocline, indicating that the application of TEX86 to reconstruct seawater temperature should be carefully appraised in coastal environments with strong water column stratification.

Modelling vertical concentration distributions of solids suspended in turbulent visco-plastic fluid

Abstract Vertical concentration distributions of solids conveyed in Newtonian fluids can be modelled using Rouse-Schmidt type distributions. Observations of solids conveyed in turbulent low Reynolds number visco-plastic carriers, suggest that solids are more readily suspended than their Newtonian counterparts, producing higher concentrations in the centre of the pipe. A Newtonian concentration profile model was adapted to include typical turbulent viscosity distributions within the pipe and particle motion calculated using non-Newtonian sheared settling. Predictions from this and the unmodified model, using the same wall viscosity, are compared with the chord averaged profile extracted from tomographic data obtained using a 50 mm horizontal pipe.

Application of homotopy analysis method to the determination of vertical sediment concentration distribution with shear-induced diffusivity

Application of homotopy analysis method to the determination of vertical sediment concentration distribution with shear-induced diffusivity

Meteorology and topographic influences on nocturnal ozone increase during the summertime over Shaoguan, China

Ozone (O3) is a typical photochemical product, generally with a maximum value in the late afternoon and a minimum value at night. This study aimed to investigate the variation characteristics of nocturnal O3 in a subtropical urban city (Shaoguan, Guangdong Province, China). The measurement campaigns were conducted from 23 July to July 28, 2020. O3 lidar, aerosol lidar, and wind profile lidar were utilised to detect the vertical distributions of the O3 concentrations, aerosol extinction coefficient, and wind velocity. The topographic features, pollutant data (PM10, PM2.5, O3, SO2, NO2, and CO), and meteorological parameters (temperature, humidity, wind speed, and wind direction) were also analysed. The results showed that the concentration of nocturnal O3 over Shaoguan peaked at midnight. The horizontal wind was dominated by southwest and south winds, and the vertical wind was dominated by downdrafts during the fixed-point observations in Shaoguan. Horizontal transport might have a high impact on the increase in the nocturnal O3 because of high pollutant emissions in upwind cities. This was further justified by the 24-h back trajectories of the air mass generated by the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model. Vertical transport of O3 in the lower or middle troposphere might be induced by the subtropical high and nocturnal mountain-valley breezes. Thus, the vertical mixing of O3 affects the O3 concentration at night.

Effects of non-locality on unsteady nonequilibrium sediment transport in turbulent flows: A study using space fractional ADE with fractional divergence

This study aims to develop a mathematical model that can describe the vertical distribution of suspended sediment particles in an open channel turbulent flow under unsteady nonequilibrium condition with non-local mixing effect. A space non-local transport of sediment is considered that arises due to turbulent bursting where the hopping height of a particle is not limited to a small distance as described by classical theory of turbulence, rather it can jump upto any height. To take into account this fact unlike previous researchers who used Rouse equation, Hunt equation or traditional advection–diffusion equation as the governing equation, the present study uses fractional advection–diffusion equation (fADE) where space fractional derivative for the local diffusive flux has been used that counts the effect of non-locality. The fractional derivative is considered in Caputo sense and the order α of the fractional derivative corresponds to α-order Le´vy stable distribution with value 1<α≤2. The non-local effect has been considered in the boundary conditions as well as in the non-linear models of sediment diffusivity. Four types of sediment diffusivity are considered which are generalized non-linear models for broad applicability of the study. The fADE together with the boundary and initial conditions, is solved by Chebyshev collocation method and Euler backward method. This proposed method is unconditionally convergent and converges more rapidly than other previous methods used in similar studies. Effects of non-local mixing have been investigated for transient and bottom concentration distributions. Proposed models have been validated for sediment distribution under steady and unsteady condition with existing experimental data and satisfactory results are obtained for all choices of sediment diffusivity. The variation of transient and bottom concentration with non-local effects are physically justified. Validation results show that the model can be applied to describe vertical concentration distribution in unsteady and steady turbulent flows in practical situation.

Wind Effects for Floating Algae Dynamics in Eutrophic Lakes

Wind-speed decline is an important impact of climate change on the eastern Asian atmospheric circulation. Although wind does not determine algae biomass in eutrophic lakes, it is a decisive factor in the formation and severity of algae blooms. Based on 2000–2018 MODIS images, this study compared the effects of wind speed on algal blooms in three typical eutrophic lakes in China: Lake Taihu, Lake Chaohu and Lake Dianchi. The results indicate that climate change has different effects on the wind speed of the three lakes, but a common effect on the vertical distribution of algae. A wind speed of 3.0 m/s was identified as the critical threshold in the vertical distribution of chlorophyll-a concentrations in the three study lakes. The basic characteristics of the periodic variation of wind speed were different, but there was a significant negative correlation between wind speed and floating algal bloom area in all three lakes. In addition, considering lake bathymetry, wind direction could be used to identify locations that were particularly susceptible to algae blooms. We estimated that algal bloom conditions will worsen in the coming decades due to the continuous decline of wind, especially in Lake Taihu, even though the provincial and national governments have made major efforts to reduce eutrophication drivers and restore lake conditions. These results suggest that early warning systems should include a wind-speed threshold of 3.0 m/s to improve control and mitigation of algal blooms on these intensively utilized lakes.

Spatial Variation of Organic Carbon Stocks in Peat Soils and Gleyzems in the Northeast of Sakhalin Island

Stocks of organic carbon in the northeast of Sakhalin Island average 109.8 kg/m2 in medium-deep oligotrophic peat soils, 75.8 kg/m2 in oligotrophic peat gley soils, 20.9–42.7 kg/m2 in peat gleyzems, and 16.6 kg/m2 in gleyzems. The vertical distribution of volumetric concentrations and the carbon stocks in different subtypes of peat soils and gleyzems have been studied. Linear regression equations have been developed to estimate carbon stocks in dependence on the depth of the peat layer. The coefficients of variation of the carbon stocks on test plots of 50 × 50 m in size increase in the following order: medium-deep oligotrophic peat soils (3.1–7.3%) < oligotrophic peat gley soils (3.3–12.9%) < peat gleyzems (9.2–21.7%) < gleyzems (22.9%). The proportion of the carbon stock variances has been estimated for three spatial scales (50 × 50 m, 5 × 5 km, and 10 × 10 km) with the use of the hierarchical analysis of variance. The required number of sampled profiles for reliable data on the mean carbon stocks in peat soils and gleyzems has been estimated. Nomograms for determining the least significant difference between the estimates of the mean soil carbon stocks have been proposed for studies with a small number of samples.

Long-Term Measurements of Radon and Thoron Exhalation Rates from the Ground Using the Vertical Distributions of Their Activity Concentrations.

A long-term measurement technique of radon exhalation rate was previously developed using a passive type radon and thoron discriminative monitor and a ventilated type accumulation chamber. In the present study, this technique was applied to evaluate the thoron exhalation rate as well, and long-term measurements of radon and thoron exhalation rates were conducted for four years in Gifu Prefecture. The ventilated type accumulation chamber (0.8 × 0.8 × 1.0 m3) with an open bottom was embedded 15 cm into the ground. The vertical distributions of radon and thoron activity concentrations from the ground were obtained using passive type radon-thoron discriminative monitors (RADUETs). The RADUETs were placed at 1, 3, 10, 30, and 80 cm above the ground inside the accumulation chamber. The measurements were conducted from autumn 2014 to autumn 2018. These long-term results were found to be in good agreement with the values obtained by another methodology. The radon exhalation rates from the ground showed a clearly seasonal variation. Similar to findings of previous studies, radon exhalation rates from summer to autumn were relatively higher than those from winter to spring. In contrast, thoron exhalation rates were not found to show seasonal variation.

Nitrogen Oxides Spatial Distribution and Emissions with Mobile Multi-Axis Differential Optical Absorption Spectroscopy in Wuhan City

For NOx, pollutions in Wuhan during the outbreak of COVID-19, we applied a mobile MAX-DOAS and a portable ultraviolet DOAS to cooperatively measure NOx, concentration in the third ring road of Wuhan from Feb. 29th to Mar. 14th, 2020. The mobile MAX-DOAS acquired the vertical column concentration (VCD) distribution of NO2 along its course and the portable ultraviolet DOAS measured the NO and NO2 concentrations to calculate [NOx]/[NO2]. Then, the NOx emission flux and its error of the third ring road of Wuhan were calculated in conjunction with the data of the wind field. The results show that the NO, emission flux during the measurements in the third ring of Wuhan ranges from 7.78 mol/s to 15.71 mol/s, about 10.78 mol/s on average. Compared with the average [NOx]/[NO2], the real-time [NOx]/[NO2] along the route of the mobile MAX-DOAS derived from the portable ultraviolet DOAS could effectively reduce the error of NOx emission flux caused by the [NOx,]/[NO2] error. However, this method is not recommended in scenarios with substantial near-surface NOx emission sources.

EFFECT OF GALLERIES ON THE WIND FLOW STRUCTURE AND POLLUTANT TRANSPORT WITHIN STREET CANYONS WITH OR WITHOUT FACADE ROUGHNESS ELEMENTS (BALCONIES)

This paper investigates how the structure of the flow field and the vertical distribution of the pollutant concentration near the wall facades of street canyons are affected by the presence of some elements such as street level galleries. Numerical results are presented for various gallery geometries in combination with facade roughness elements (balconies) for a canyon of an aspect ratio equal to h/w=2.33. The results were obtained by a Computational Fluid Dynamics (CFD) simulation employing the ANSYS-FLUENT suite that incorporated the k-e turbulent (RNG) model. The simulation generated several flow structures inside the canyon (mainly vortices), whose characteristic properties (e.g. number, strength and size) are discussed in terms of the effect of the galleries on the flow field structure and the roughness generated by the building façade balconies. The results indicate a significant influence on both the flow field structure and the mass concentration distribution of the polluting particles.

Seasonal Stages of Chlorophyll‐a Vertical Distribution and Its Relation to the Light Conditions in the Black Sea From Bio‐Argo Measurements

AbstractThe year‐to‐year seasonal variability of the vertical distribution of concentration of chlorophyll‐a (Chla) in the Black Sea, its relation to light (photosynthetically available irradiance [PAR]), and mixing conditions were studied based on the 6‐year (2014–2019) measurements of Bio‐Argo floats. Variations in PAR caused by changes in incoming solar radiation and light attenuation determine the position of the deep chlorophyll maximum (DCM). During all seasons, the DCM was located between isolume of daily integrated PAR of 0.080 and 10.0 mole photons m−2 d−1. Analysis of Bio‐Argo data allowed to distinguish seven different stages of Chla seasonal variability. In February, the minimum of Chla in the entire water column was often observed in areas with a deep mixed layer (Stage 1), followed by the March early spring peak, occupying both the mixed layer and the seasonal thermocline (Stage 2). In April–May, Chla decreased throughout the 0–40 m layer, which was accompanied by the maximum in light penetration and an increase in Chla in the deepest layers (Stage 3). In summer, two deep peaks of Chla were distinguished: the first, a thin and shallow peak in June, and the second, a large and deeper peak in August (Stage 4 and 5). The August peak was followed by the deepest seasonal minimum of Chla in September–October, coincided with the autumn rise of the zooplankton biomass (Stage 6). Autumn–winter convection in November–January led to the third seasonal peak of Chla (Stage 7). The study discusses the role of various abiotic and biotic factors in the formation of each of these stages.

Sediment diffusion coefficient model for predicting the vertical distribution of suspended sediment concentration in uniform open-channel flows

This paper presents a theoretical model for predicting the vertical distribution of suspended sediment concentrations in open-channel flows. The model developed uses a new sediment diffusivity coefficient obtained by the application of the Itakura and Kishi correction method to the Kerssens sediment diffusivity profile. The new coefficient is calculated using composite operators applied to the Rouse sediment diffusivity profile. The diffusivity profile proposed increases as a parabolic profile from zero at the bottom to a maximum value in the lower part of the flow, and then decreases slowly towards the water surface without reaching zero. The maximal value is calculated at a level between 20 and 30% of the total water depth as explained previously by Coleman. Based on this diffusivity profile, a theoretical formulation for computing sediment concentration is derived analytically, using the well-known convection–diffusion equation. We compare results from the proposed model with experimental measurements and existing theoretical models, obtained by previous researchers, in order to evaluate the applicability of the present model to predict particle concentration profiles in open-channel flows. The computed values of sediment concentrations are in good agreement with the experimental data reported in the literature.

Spatio-Temporal Validation of AIRS CO2 Observations Using GAW, HIPPO and TCCON

Carbon dioxide (CO2) is a significant atmospheric greenhouse gas and its concentrations can be observed by in situ surface stations, aircraft flights and satellite sensors. This paper investigated the ability of the CO2 satellite observations to monitor, analyze and predict the horizontal and vertical distribution of atmospheric CO2 concentration at global scales. CO2 observations retrieved by an Atmospheric Infrared Sounder (AIRS) were inter-compared with the Global Atmosphere Watch Program (GAW) and HIAPER Pole-to-Pole Observations (HIPPOs), with reference to the measurements obtained using high-resolution ground-based Fourier Transform Spectrometers (FTS) in the Total Carbon Column Observing Network (TCCON) from near-surface level to the mid-to-high troposphere. After vertically integrating the AIRS-retrieved values with the column averaging kernels of TCCON measurements, the AIRS observations are spatio-temporally compared with HIPPO-integrated profiles in the mid-to-high troposphere. Five selected GAW stations are used for comparisons with TCCON sites near the surface of the Earth. The results of AIRS, TCCON (5–6 km), GAW and TCCON (1 km) CO2 measurements from 2007 to 2013 are compared, analyzed and discussed at their respective altitudes. The outcomes indicate that the difference of about 3.0 ppmv between AIRS and GAW or other highly accurate in situ surface measurements is mainly due to the different vertical altitudes, rather than the errors in the AIRS. The study reported here also explores the potential of AIRS satellite observations for analyzing the spatial distribution and seasonal variation of CO2 concentration at global scales.

Vertical distribution of radiocesium concentrations among crown positions and year-to-year variation in four major tree species after the Fukushima Daiichi Nuclear Power Plant accident

To evaluate the distribution of radiocesium (137Cs) among crown positions in trees after the Fukushima Daiichi Nuclear Power Plant accident, we collected foliage and branch samples from different crown positions of four major tree species (Chamaecyparis obtusa, Cryptomeria japonica, Pinus densiflora, and Quercus serrata) from 2011 to 2019 in northeast Japan. We divided the samples into current-year and more than 1-year-old groups (called old foliage and old branches), which sometimes included directly contaminated parts. The 137Cs activity concentration in dry foliage and branches was measured using a germanium semiconductor detector. There were complex differences in the relative 137Cs activity concentration among species and organ types (i.e., foliage and branches) among crown positions. The relative 137Cs activity concentration in current-year foliage was higher in the upper crowns of C. obtusa, but higher in lower crown positions in C. japonica. No differences among crown positions were observed in P. densiflora and Q. serrata. In current-year branches, the relative 137Cs concentration in Q. serrata was similar among crown positions but higher in the upper crown in P. densiflora. The concentrations in old foliage and old branches in all species tended to be higher in the lower crown. The factors causing these interspecific and organ type differences among crown positions may be related to the organ turnover rate, dilution effect due to different growth rates, and potassium distribution within the crown. No year-to-year variation was observed in most foliage and branches in all species, except for current-year branches of Q. serrata, old foliage in C. japonica and P. densiflora, and old branches in P. densiflora. Our long-term data on the interspecific and inter-organ patterns of contamination, focusing on variation among crown positions and year-to-year trends, might help to improve the estimation of 137Cs deposition and dynamics in polluted forest ecosystems.

Spatiotemporal distribution of nitrous oxide (N2O) emissions from cascade reservoirs in Lancang‐Mekong River Yunnan section, Southwestern China

AbstractThe current issue of river damming causing the release of greenhouse gas nitrous oxide (N2O) from reservoirs has led to a debate over whether hydropower can still provide clean energy. In January (dry season) and August 2019 (wet season), we detected the N2O concentrations from cascade reservoirs in Lancang‐Mekong River Yunnan section by using static headspace gas chromatography and estimated the emission flux by the boundary layer approach to explore the influencing factors, especially the impact of cascade reservoirs development and operation. In the Lancang River (Yunnan section), the longitudinal distribution of N2O concentration along the cascade reservoirs showed seasonal differences. The average concentrations of N2O during the dry season and the wet season were 13.50 ± 2.00 nmol/L and 16.40 ± 4.10 nmol/L, respectively. The reservoirs with thermal stratification in both seasons were the Xiaowan (XW), Nuozhadu (NZD), and Jinghong (JH) reservoirs. The vertical distribution of N2O concentration was depth dependent (i.e., the deeper the location, the higher the concentration) in reservoirs with thermal stratification and uniform in reservoirs without thermal stratification. Dissolved oxygen (DO), water temperature, and other biogenic elements were the main factors affecting N2O distribution. The average N2O emission flux in the cascade reservoirs was 12.80 ± 2.60 μmol m2·day−1 during the dry season and 16.10 ± 4.75 μmol m2·day−1 during the wet season. The annual average N2O emission fluxes of all reservoirs were in an order of JH &gt; XW &gt; Dachaoshan (DCS) &gt; NZD &gt; Miaowei (MW) &gt; Gongguoqiao (GGQ) &gt; Manwan (Man W). In 2019, a total of 3.37 × 106 mol year−1 (94.39 ton N2O‐N year−1) was released from the water surface of the cascade reservoirs, which accounted for approximately 0.31% of the total N2O emissions from reservoirs worldwide. This study shows the cascade reservoirs development and operations have made the Lancang River (Yunnan section) a major area for N2O emissions.

Aerosol data assimilation in the MOCAGE chemical transport model during the TRAQA/ChArMEx campaign: lidar observations

Abstract. This paper presents the first results about the assimilation of CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) extinction coefficient measurements onboard the CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) satellite in the MOCAGE (MOdèle de Chimie Atmosphérique à Grande Echelle) chemistry transport model of Météo-France. This assimilation module is an extension of the aerosol optical depth (AOD) assimilation system already presented by Sič et al. (2016). We focus on the period of the TRAQA (TRAnsport à longue distance et Qualité de l’Air dans le bassin méditerranéen) field campaign that took place during summer 2012. This period offers the opportunity to have access to a large set of aerosol observations from instrumented aircraft, balloons, satellite and ground-based stations. We evaluate the added value of CALIOP assimilation with respect to the model free run by comparing both fields to independent observations issued from the TRAQA field campaign. In this study we focus on the desert dust outbreak which happened during late June 2012 over the Mediterranean Basin (MB) during the TRAQA campaign. The comparison with the AERONET (Aerosol Robotic Network) AOD measurements shows that the assimilation of CALIOP lidar observations improves the statistics compared to the model free run. The correlation between AERONET and the model (assimilation) is 0.682 (0.753); the bias and the root mean square error (RMSE), due to CALIOP assimilation, are reduced from −0.063 to 0.048 and from 0.183 to 0.148, respectively. Compared to MODIS (Moderate-resolution Imaging Spectroradiometer) AOD observations, the model free run shows an underestimation of the AOD values, whereas the CALIOP assimilation corrects this underestimation and shows a quantitative good improvement in terms of AOD maps over the MB. The correlation between MODIS and the model (assimilation) during the dust outbreak is 0.47 (0.52), whereas the bias is −0.18 (−0.02) and the RMSE is 0.36 (0.30). The comparison of in situ aircraft and balloon measurements to both modelled and assimilated outputs shows that the CALIOP lidar assimilation highly improves the model aerosol field. The evaluation with the LOAC (Light Optical Particle Counter) measurements indicates that the aerosol vertical profiles are well simulated by the direct model but with a general underestimation of the aerosol number concentration, especially in the altitude range 2–5 km. The CALIOP assimilation improves these results by a factor of 2.5 to 5. Analysis of the vertical distribution of the desert aerosol concentration shows that the aerosol dust transport event is well captured by the model but with an underestimated intensity. The assimilation of CALIOP observations allows the improvement of the geographical representation of the event within the model as well as its intensity by a factor of 2 in the altitude range 1–5 km.