High Atmospheric Concentrations Research Articles

Recent shift from dominant nitrogen to CO2 fertilization control on the growth of mature Qinghai spruce in China's Qilian Mountains

Terrestrial vegetation growth is stimulated by rising atmospheric CO2 concentration, a warmer climate, and increased soil nutrient availability. However, as plants age, progressive nutrient limitation is known to occur, especially in mature forests where soil nitrogen is deficient. Yet the long-term growth response of mature trees to rising CO2 accompanied by changing climate and nitrogen availability in semi-arid mountain regions is unclear. Here we used tree-ring widths and stable carbon (δ13C) and nitrogen (δ15N) isotopes to investigate the drivers of radial growth of mature Qinghai spruce (Picea crassifolia) in the central Qilian Mountains, northwest China, from 1840 through 2019. Tree growth benefited from improved nitrogen availability, chiefly via changes in bioavailable nitrogen pools modified by a favorable climate during 1930–1964. Enhanced intrinsic water-use efficiency (iWUE), driven by reduced stomatal conductance (gs) related to water deficit, lead to radial growth declines in 1985–2002. Recent acceleration of tree growth was largely attributed to a CO2 fertilization effect through enhanced iWUE during 2003–2019. Nitrogen availability was positively related to tree growth from the 1920s onward until greater CO2 fertilization ensued from 2000 onward. Hence, the negative effects of low nitrogen availability on growth could be mitigated or reversed by a high atmospheric CO2 concentration and warmer climate conditions. Our results suggest that mature spruce forests still harbor potential to increase ecosystem-level carbon sequestration and thereby partially mitigate climate warming. Such a nature-based solution in drought-prone forests would be achieved under warmer-wetter climate conditions in northwest China.

An Online Downscaling Method to Simulate High Resolution Atmospheric Concentrations of Pesticides with the 3D Chemistry-Transport Model CHIMERE: Application and Evaluation

High resolution databases on atmospheric concentrations of pesticides are necessary in order to perform epidemiological studies but there is currently no modeling method to provide high resolution mapping of pesticides concentrations over a whole region. In this study, we propose an online downscaling method for CHIMERE to perform simulations at a sub-kilometer resolution. The main idea of this downscaling approach is to redistribute or interpolate some information simulated on the coarse grid to simulate the transport over a finer subgrid. The performance of the downscaling is analyzed by comparing the CHIMERE nested simulation results at 0.02° and CHIMERE simulation results downscaled from 0.1° to 0.02°.By applying this method to S-metolachlor, we diagnosed an error generated by the downscaling of a few percents on both background and hotspot concentrations. The method was used to simulate concentrations over France at a resolution of 0.004° with a limited increase of the computational time. Based on these simulations, we estimated that around 3 000 inhabitants were exposed to concentrations of S-metolachlor above 10 ng/m3 from April 15th to May 15th 2014.

East Asian summer monsoon variations across the Miocene−Pliocene boundary recorded by sediments from the Guide Basin, northeastern Tibetan Plateau

Records of atmospheric carbon dioxide concentration, sea-surface temperature, and global vegetation show that Earth’s climate and environment changed significantly during the late Miocene−early Pliocene. Understanding the environmental response to insolation forcing during this transitional period may provide insights into future environmental variations resulting from the perturbation of the global carbon cycle caused by fossil fuel combustion. However, terrestrial paleoclimate records capable of resolving orbital time-scale environmental variations are mostly from Europe, especially from the region around the Mediterranean Sea. Here, we present high-resolution records of grain size, black carbon, and geochemistry from a sedimentary sequence from the northeastern margin of the Tibetan Plateau, where precipitation is mainly via the East Asian summer monsoon. We observed increases in sediment accumulation rate and black carbon mass accumulation rate at ca. 5.3 Ma, which we interpret as the result of intensified seasonal precipitation associated with the strengthening of the East Asian summer monsoon; concurrently, precessional and obliquity cycles became more prominent during the early Pliocene. Our results suggest that, in response to current and future high atmospheric carbon dioxide concentrations, changes in the East Asian summer monsoon are likely to result in increased precipitation and seasonality within its region of influence.

Effect of Temperature on Growth, Quality, Yield Attributing Characters and Yield of Rice – A Review

Rice (Oryza sativa L.) is the second most important food in the world after wheat. Most rice is now grown in areas where the temperature is higher than the optimum growing temperature (28/22°C); therefore, a further increase in average temperature or high temperature occurring in the sensitive phase of the crop can affect growth and yield. Clutter. For every 1°C increase in daytime maximum/night minimum temperature from 28°C/21°C to 34°C/27°C, rice yield decreases by 7% to 8%. Additionally, the benefits that crops derive from high atmospheric carbon dioxide concentrations must be lost due to warming. The thermal stability of cell membranes is thought to correlate well with yield performance. Temperature is important in photosynthesis, but too hot can cause reduced photosynthesis of leaves and reduced distribution of dry matter to shoots and roots. The disadvantage of temperature is not limited to the above-ground rice. The underground area is affected, if not more, by the flood, and the temperature of the soil changes due to the heat. Future increases in global temperatures threaten people worldwide who depend on crops for their health and food security. In the past, the stress of the crisis on rice production focused on the rice crop. This review highlights the importance of rice in the world, the effect of high temperature on the growth, quality, yield and properties of rice, and the need for future research.

Impact of Particulate Matter (PM10 and PM2.5) from a Thermoelectric Power Plant on Morpho-Functional Traits of Rhizophora mangle L. Leaves

A conventional thermoelectric plant (TP) in the sandy bar of the Tampamachoco Lagoon (Gulf of Mexico slope) emits particulate matter (PM) transporting trace metals that affect a mangrove forest. Wind transports the emission plume from north to south in the northerly wind season (NWS); the dry season (DS) showed calm periods. We analyzed whether PM2.5 and PM10 emissions from the TP and their trace metals impact Rhizophora mangle leaves. The experimental design included three sampling sites along the main lagoon axis (north to south) during the NWS and DS. Mangrove leaves were collected; PM was obtained with a cascade impactor and trace elements were analyzed by atomic absorption spectrophotometry. Leaves were measured and tested for metal and chlorophyll content, and for metal detection with SEM-EDX. Calm periods in the DS promote high atmospheric PM concentrations. Wet deposition in the NWS caused the highest trace metal deposition on mangrove leaves. A north-to-south gradient was identified on the mangrove forest, being the south site of the lagoon where lower chlorophyll and leaf area, higher stomatal width and density, and higher Cd concentrations were recorded. The morpho-physiological modifications observed on mangrove leaves affect functions such as photosynthesis and gas exchange.

Seasonal climate conditions impact the effectiveness of improving photosynthesis to increase soybean yield.

Photosynthetic stimulations have shown promising outcomes in improving crop photosynthesis, including soybean. However, it is still unclear to what extent these changes can impact photosynthetic assimilation and yield under long-term field climate conditions. In this paper, we present a systematic evaluation of the response of canopy photosynthesis and yield to two critical parameters in leaf photosynthesis: the maximum carboxylation rate of ribulose-1,5-bisphosphate carboxylase/oxygenase (Vcmax) and the maximum electron transport of the ribulose-1,5-bisphosphate regeneration rate (Jmax). Using the field-scale crop model Soybean-BioCro and ten years of observed climate data in Urbana, Illinois, U.S., we conducted sensitivity experiments to estimate the changes in canopy photosynthesis, leaf area index, and biomass due to the changes in Vcmax and Jmax. The results show that 1) Both the canopy photosynthetic assimilation (An) and pod biomass yields were more sensitive to the changes in Jmax, particularly at high atmospheric carbon-dioxide concentrations ([CO2]); 2) Higher [CO2] undermined the effectiveness of increasing the two parameters to improve An and yield; 3) Under the same [CO2], canopy light interception and canopy respiration were key factors that undermined improvements in An and yield; 4) A canopy with smaller leaf area index tended to have a higher yield improvement, and 5) Increases in assimilations and yields were highly dependent on growing-season climatic conditions. The solar radiation, temperature, and relative humidity were the main climate drivers that impacted the yield improvement, and they had opposite correlations with improved yield during the vegetative phase compared to the reproductive phase. In a world with elevated [CO2], genetic engineering crop photosynthesis should focus more on improving Jmax. Further, long-term climate conditions and seasonal variations must be considered to determine the improvements in soybean canopy photosynthesis and yield at the field scale. Quantifying the effectiveness of changing Vcmax and Jmax helps understand their individual and combined contributions to potential improvements in assimilation and yield. This work provides a framework for evaluating how altering the photosynthetic rate parameters impacts soybean yield and assimilation under different seasonal climate scenarios at the field scale.

Melatonin mediates elevated carbon dioxide-induced photosynthesis and thermotolerance in tomato.

Increasing carbon dioxide (CO2 ) promotes photosynthesis and mitigates heat stress-induced deleterious effects on plants, but the regulatory mechanisms remain largely unknown. Here, we found that tomato (Solanum lycopersicum L.) plants treated with high atmospheric CO2 concentrations (600, 800, and 1000 µmol mol-1 ) accumulated increased levels of melatonin (N-acetyl-5-methoxy tryptamine) in their leaves and this response is conserved across many plant species, including Arabidopsis, rice, wheat, mustard, cucumber, watermelon, melon, and hot pepper. Elevated CO2 (eCO2 ; 800 µmol mol-1 ) caused a 6.8-fold increase in leaf melatonin content, and eCO2 -induced melatonin biosynthesis preferentially occurred through chloroplast biosynthetic pathways in tomato plants. Crucially, manipulation of endogenous melatonin levels by genetic means affected the eCO2 -induced accumulation of sugar and starch in tomato leaves. Furthermore, net photosynthetic rate, maximum photochemical efficiency of photosystem II, and transcript levels of chloroplast- and nuclear-encoded photosynthetic genes, such as rbcL, rbcS, rbcA, psaD, petB, and atpA, significantly increased in COMT1 overexpressing (COMT1-OE) tomato plants, but not in melatonin-deficient comt1 mutants at eCO2 conditions. While eCO2 enhanced plant tolerance to heat stress (42°C) in wild-type and COMT1-OE, melatonin deficiency compromised eCO2 -induced thermotolerance in comt1 plants. The expression of heat shock proteins genes increased in COMT1-OE but not in comt1 plants in response to eCO2 under heat stress. Further analysis revealed that eCO2 -induced thermotolerance was closely linked to the melatonin-dependent regulation of reactive oxygen species, redox homeostasis, cellular protein protection, and phytohormone metabolism. This study unveiled a crucial mechanism of elevated CO2 -induced thermotolerance in which melatonin acts as an essential endogenous signaling molecule in tomato plants.

Investigating the hygroscopicities of calcium and magnesium salt particles aged with SO2 using surface plasmon resonance microscopy

The hygroscopicities of calcium and magnesium salts strongly affect the environment and climate, but the aging products of these salts at high relative humidities (RHs) are still poorly understood. In this study, surface plasmon resonance microscopy (SPRM) was used to determine the hygroscopic growth factors (GFs) of Ca(NO3)2 and Mg(NO3)2 separately or mixed with galactose at different mass ratios at different RHs before and after aging. For all particles, the measured GFs showed no indication of deliquescence across the range of RHs tested, and overall hygroscopicity was clearly lower after than before aging. The Ca(NO3)2 and Mg(NO3)2 GFs at 90 % RH were 1.80 and 1.66, respectively, before aging and 1.33 and 1.42, respectively, after 4 h aging, meaning aging decreased the GFs by 26.11 % and 14.46 %, respectively. Aging decreased the hygroscopicity because insoluble or sparingly soluble substances (CaSO3, CaSO4, MgSO3) formed and strongly changed the overall hygroscopicity. For bicomponent aerosols with different mass ratios, the GFs (calculated using the Zdanovskii-Stokes-Robinson method) of the other components except galactose at 90 % RH after 1 h aging were all lower, respectively, than the measured GFs of pure Ca(NO3)2 and Mg(NO3)2 after aging for 1 h, especially with the mass ratio of 1:2, their GFs have decreased by 14.63 % and 7.50 %, respectively. Subsequently, Ion chromatograms indicated that the peak area ratio of SO42− to NO3− ratios were higher for the aged bicomponent particles than aged single-component particles, possibly because adding galactose improved the gas–liquid state stability during drying after the aging process and therefore promoted nitrate consumption and sulfate formation. The results indicated that organic components may play important roles in heterogeneous reactions between trace gases and multicomponent aerosols and should be considered in evaluating the impacts on submicron aerosol composition of high atmospheric SO2 concentrations at high humidities.

Increased fire activity under high atmospheric oxygen concentrations is compatible with the presence of forests

Throughout Earth’s history, the abundance of oxygen in our atmosphere has varied, but by how much remains debated. Previously, an upper limit for atmospheric oxygen has been bounded by assumptions made regarding the fire window: atmospheric oxygen concentrations higher than 30–40% would threaten the regeneration of forests in the present world. Here we have tested these assumptions by adapting a Dynamic Global Vegetation Model to run over high atmospheric oxygen concentrations. Our results show that whilst global tree cover is significantly reduced under high O2 concentrations, forests persist in the wettest parts of the low and high latitudes and fire is more dependent on fuel moisture than O2 levels. This implies that the effect of fire on suppressing global vegetation under high O2 may be lower than previously assumed and questions our understanding of the mechanisms involved in regulating the abundance of oxygen in our atmosphere, with moisture as a potentially important factor.

Distinct effects of Tibetan Plateau growth and global cooling on the eastern and central Asian climates during the Cenozoic

The evolution of the climate in eastern and central Asia during the Cenozoic was affected by regional paleogeographic developments and global climate change. Previous studies have mainly investigated the effects of Tibetan Plateau (TP) growth and global cooling for specific time periods. However, the respective contributions of these two factors over time are still poorly understood. In this study, we comprehensively compared the effects of TP growth and secular climate change by integrating existing paleobotanical records and model results across a total of 67 experiments. Our results demonstrate that the effects of TP growth and global cooling on the eastern and central Asian climates differed. During the early Eocene, high atmospheric CO2 concentrations contributed greatly to the relatively wet conditions in eastern and central Asia. Subsequent global cooling tended to cause long-term aridification in eastern Asia. By comparison, TP growth was the key factor for the increasing precipitation in eastern Asia and the decreasing precipitation in central Asia between the late Oligocene and the early Miocene. High atmospheric CO2 concentrations contributed to the increased wetness in eastern Asia in the geological past, and this fact has far-reaching implications for future wetter conditions in this region under anthropogenic forcing.

Elevation-dependent temperature response in early Eocene using paleoclimate model experiment

Mountains become warmer with elevation in response to greenhouse gas warming, an effect known as elevation-dependent warming. The Eocene is considered a replica of the future climate in an epoch with high atmospheric carbon dioxide concentration (CO2). Therefore, the topographic features of the Eocene strata are of interest. However, obtaining proxy data for mountain regions during the Eocene hothouse is challenging. Paleoclimate model simulation is an effective tool for exploring past climate change. Therefore, we conducted sensitivity experiment simulations employing the Community Earth System Model version 1.2 forced by proxy-estimated CO2 levels. This is the first Eocene study demonstrating the elevation-dependent temperature changes and illustrated using the surface energy budget decomposition. Here five major mountain ranges have been chosen based on their paleogeographic continental location. We found a nonlinear response of elevation-dependent temperature change to CO2 concentrations regulated by seasonal variations. The radiative and non-radiative feedback compensation is responsible for the elevation-dependency temperature changes. Our results suggest temperature perturbations regulate elevation-dependent changes in skin temperature through a combination of feedback under greenhouse warming in the early Eocene. These findings also show future paradox response exhibiting elevation-dependent cooling overall mountain regions due to lower elevation warming.

Chemical characteristics and deposition amounts of carbonaceous species and inorganic ions in precipitation in the Bangkok Metropolitan Region

A comprehensive study on the chemical characteristics and deposition fluxes of precipitation components, including water-insoluble organic carbon (WIOC), water-soluble organic carbon (WSOC), and elemental carbon (EC), including Char-EC and Soot-EC, and major inorganic ions, was conducted from September 2015 to March 2017 at suburban (AIT) and urban (PCD) sites in the Bangkok Metropolitan Region (BMR), Thailand. This is the first study of this kind conducted in tropical areas. To study the scavenging effect of atmospheric particles by wet deposition, atmospheric particulate carbonaceous components were simultaneously measured. The average concentrations of carbonaceous components in precipitation were higher at AIT than at PCD (Bangkok City Center). The contribution of WIOC to total organic carbon (OC) in precipitation was more important at AIT than at PCD sites, whereas the opposite was observed for the contribution of EC. The concentrations of all components in precipitation during the dry season were higher than those during the wet season. The washout processes efficiently removed atmospheric carbonaceous components in the study area, a tropical urban region with a high atmospheric particle concentration. The scavenging ratios (SRs) followed the order of main anthropogenic ions (NO3− and SO42−) > OC > Soot-EC > Char-EC. The annual mean SRs of NO3−, SO42−, OC, Soot-EC, and Char-EC were 1.61, 1.13, 0.75, 0.09, and 0.03 at AIT and 0.96, 1.04, 0.63, 0.08, and 0.03 at PCD, respectively. The washout process was dominant for water-insoluble components (EC and WIOC), whereas the rain-out process was relatively more prominent for water-soluble components (WSOC, SO42− and NO3−). The wet deposition amounts of carbonaceous and main inorganic anions ranked in the order of NO3−> WSOC> SO42− >WIOC>EC, suggesting that the influence of secondary particles was more significant than that of the primary particles. The volume-weighted average pH values of rainwater at suburban and urban sites were 6.25 and 6.04, respectively. NO3− was observed to play a relatively more important role than SO42− in the acidity of rainwater in the BMR. The acidity in the precipitation was almost neutralized by the alkalinity.

Continental weathering and recovery from ocean nutrient stress during the Early Triassic Biotic Crisis

Following the latest Permian extinction ∼252 million years ago, normal marine and terrestrial ecosystems did not recover for another 5-9 million years. The driver(s) for the Early Triassic biotic crisis, marked by high atmospheric CO2 concentration, extreme ocean warming, and marine anoxia, remains unclear. Here we constrain the timing of authigenic K-bearing mineral formation extracted from supergene weathering profiles of NW-Pangea by Argon geochronology, to demonstrate that an accelerated hydrological cycle causing intense chemical alteration of the continents occurred between ∼254 and 248 Ma, and continued throughout the Triassic period. We show that enhanced ocean nutrient supply from this intense continental weathering did not trigger increased ocean productivity during the Early Triassic biotic crisis, due to strong thermal ocean stratification off NW Pangea. Nitrogen isotope constraints suggest, instead, that full recovery from ocean nutrient stress, despite some brief amelioration ∼1.5 million years after the latest Permian extinction, did not commence until climate cooling revitalized the global upwelling systems and ocean mixing ∼10 million years after the mass extinction.

Simulation of Arctic sea ice within the DeepMIP Eocene ensemble: Thresholds, seasonality and factors controlling sea ice development

The early Eocene greenhouse climate maintained by high atmospheric CO2 concentrations serves as a testbed for future climate changes dominated by increasing CO2 forcing. In particular, the early Eocene Arctic region is important in the context of future CO2 driven climate warming in the northern polar region and associated shrinking Arctic sea ice. Here, we present early Eocene Arctic sea ice simulations carried out by six coupled climate models within the framework of the Deep-Time Model Intercomparison Project (DeepMIP). We find differences in sea ice responses to CO2 changes across the ensemble and compare the results with available proxy-based sea ice reconstructions from the Arctic Ocean. Most of the models simulate seasonal sea ice presence at high CO2 levels (≥ 840 ppmv = 3× pre-industrial (PI) level of 280 ppmv). However, the threshold when sea ice permanently disappears from the ocean varies considerably between the models (from <840 ppmv to >1680 ppmv). Based on a one-dimensional energy balance model analysis we find that the greenhouse effect likely caused by increased atmospheric water vapor concentration plays an important role in the inter-model spread in Arctic winter surface temperature changes in response to a CO2 rise from 1× to 3× the PI level. Furthermore, differences in simulated surface salinity in the Arctic Ocean play an important role in the control of local sea ice formation. These differences result from different implementations of river run-off between the models, but also from differences in the exchange of waters between a brackish Arctic and a more saline North Atlantic Ocean that are controlled by the width of the gateway between both basins. As there is no geological evidence for Arctic sea ice in the early Eocene, its presence in most of the simulations with 3× PI CO2 level indicates either a higher CO2 level and/or an overly weak polar sensitivity in these models.

Relict sand wedges suggest a high altitude and cold temperature during the Early Cretaceous in the Ordos Basin, North China

ABSTRACT The Cretaceous, with relatively high atmospheric CO2 concentrations, temperatures, and sea levels, is a typical greenhouse period in the geologic history of the Earth. Recently, gradual changes in the understanding of the Early Cretaceous climate have led to the proposal of small-scale polar glaciers or cooling events in polar regions. However, the cooling events in North China at mid-latitudes are still poorly understood. In this study, 48 wedge structures that are 35-240 cm wide and from 120 cm to more than 300 cm in depth down through the bottom of Lower Cretaceous Luohe Formation conglomerate and penetrated vertically downward into Jurassic Anding Formation mudstone in the Ordos Basin, North China. According to findings, these sand wedges are distinguished by large-scale V shapes, vertical to steeply dipping laminations and pebbles, aeolian abrasion of sand grains, ventifacts, upturned host strata, and other features that are most likely the source of thermal contraction cracking in periglacial desert region. The sand wedges formed when thermal contraction cracks were filled with wind-blown deposits and other material in dry, cold, and windy regions. This record may support the hypothesis that the Ordos Basin, western North China, may have been at a high altitude and was cold during the Early Cretaceous. During the Early Cretaceous, the complex topography and climate of North China allowed the Jehol Fauna to coexist with permafrost and glaciers.

Secondary PM&amp;lt;sub&amp;gt;2.5&amp;lt;/sub&amp;gt; decreases significantly less than NO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; emission reductions during COVID lockdown in Germany

Abstract. This study estimates the influence of anthropogenic emission reductions on the concentration of particulate matter with a diameter smaller than 2.5 µm (PM2.5) during the 2020 lockdown period in German metropolitan areas. After accounting for meteorological effects, PM2.5 concentrations during the spring 2020 lockdown period were 5 % lower compared to the same time period in 2019. However, during the 2020 pre-lockdown period (winter), PM2.5 concentrations with meteorology accounted for were 19 % lower than in 2019. Meanwhile, NO2 concentrations with meteorology accounted for dropped by 23 % during the 2020 lockdown period compared to an only 9 % drop for the 2020 pre-lockdown period, both compared to 2019. SO2 and CO concentrations with meteorology accounted for show no significant changes during the 2020 lockdown period compared to 2019. GEOS-Chem (GC) simulations with a COVID-19 emission reduction scenario based on the observations (23 % reduction in anthropogenic NOx emission with unchanged anthropogenic volatile organic compounds (VOCs) and SO2) are consistent with the small reductions of PM2.5 during the lockdown and are used to identify the underlying drivers for this. Due to being in a NOx-saturated ozone production regime, GC OH radical and O3 concentrations increased (15 % and 9 %, respectively) during the lockdown compared to a business-as-usual (BAU, no lockdown) scenario. Ox (equal to NO2+O3) analysis implies that the increase in ozone at nighttime is solely due to reduced NO titration. The increased O3 results in increased NO3 radical concentrations, primarily during the night, despite the large reductions in NO2. Thus, the oxidative capacity of the atmosphere is increased in all three important oxidants, OH, O3, and NO3. PM nitrate formation from gas-phase nitric acid (HNO3) is decreased during the lockdown as the increased OH concentration cannot compensate for the strong reductions in NO2, resulting in decreased daytime HNO3 formation from the OH + NO2 reaction. However, nighttime formation of PM nitrate from N2O5 hydrolysis is relatively unchanged. This results from the fact that increased nighttime O3 results in significantly increased NO3, which roughly balances the effect of the strong NO2 reductions on N2O5 formation. Ultimately, the only small observed decrease in lockdown PM2.5 concentrations can be explained by the large contribution of nighttime PM nitrate formation, generally enhanced sulfate formation, and slightly decreased ammonium. This study also suggests that high PM2.5 episodes in early spring are linked to high atmospheric ammonia concentrations combined with favorable meteorological conditions of low temperature and low boundary layer height. Northwest Germany is a hot-spot of NH3 emissions, primarily emitted from livestock farming and intensive agricultural activities (fertilizer application), with high NH3 concentrations in the early spring and summer months. Based on our findings, we suggest that appropriate NOx and VOC emission controls are required to limit ozone, and that should also help reduce PM2.5. Regulation of NH3 emissions, primarily from agricultural sectors, could result in significant reductions in PM2.5 pollution.

Elevated Gaseous Oxidized Mercury Revealed by a Newly Developed Speciated Atmospheric Mercury Monitoring System.

Gaseous oxidized mercury (Hg2+) monitoring is one of the largest challenges in the mercury research field, where existing methods cannot simultaneously satisfy the measurement requirements of both accuracy and time precision, especially in high-particulate environments. Here, we verified that dual-stage cation exchange membrane (CEM) sampler is incapable of gaseous elemental mercury (Hg0) uptake even if particulate matter is trapped on CEM, whereas the Hg2+ capture efficiency of the sampler is more than 90%. We then developed a Cation Exchange Membrane-Coupled Speciated Atmospheric Mercury Monitoring System (CSAMS) by coupling the dual-stage CEM sampler with the commercial Tekran 2537/1130/1135 system and configuring a new sampling and analysis procedure, so as to improve the monitoring accuracy of Hg2+ and ensure the simultaneous measurement of Hg0, Hg2+, and Hgp in 2 h time resolution. We deployed the CSAMS in urban Beijing in September 2021 and observed an unprecedented elevated Hg2+ during the daytime with an average amplitude of 510 pg m-3. Using a zero-dimensional box model, the elevated Hg2+ production rate was attributed to high atmospheric oxidant concentrations, Hg0 heterogeneous and interfacial oxidation processes on the surface of atmospheric particles, or potential unknown oxidants.

Full straw incorporation into a calcareous soil increased N2O emission despite more N2O being reduced to N2 in the winter crop season

Crop straw application in combination with fertilizer nitrogen (N) dose reduction is recommended to improve crop yields and carbon sequestration in soil. This practice may also promote soil nitrous oxide (N2O) emission, thus partially counterbalancing the expected benefits. However, the full straw return effect on the reduction of soil N2O to dinitrogen (N2) is not yet well known, owing to the methodological difficulties in quantifying soil N2 fluxes against the high atmospheric N2 concentration. This study was carried out in a long-term experimental field of a calcareous soil cultivated with summer maize and winter wheat in rotation. For the three field treatments since 2006, i.e., optimal fertilizer N with and without full straw return, and the control (without N and straw application), we conducted in- or ex-situ observations on field N2O fluxes, soil N2 emissions, crop yields, soil organic carbon (SOC) contents and soil/environmental factors. During a rotation cycle, we found that soil ammonium and nitrite concentrations, moisture and temperature jointly determined the N2O emissions, while nitrate concentration, dissolvable organic carbon to nitrate-N ratio and moisture jointly dominated the N2 emissions. Compared to straw removal, the straw return promoted reduction of more soil N2O to N2 in the wheat season than in the maize season, showing increases in the N2 emissions by 57% versus − 10% (P = 0.06). Nevertheless, it significantly enhanced the N2O emissions measured in situ by approximately 137% and 21% in the wheat and maize seasons, respectively (P < 0.05). It also significantly increased the annual crop yields by 20% on average (P < 0.05). Meanwhile it tended to enhance the SOC stock (0−20 cm) by 15‰ yr−1 (P = 0.14), showing a trend of more intensive carbon sequestration than the direct soil N2O emission (−948 versus 378 kg CO2e ha−1 yr−1 on average). We conclude that the long-term full straw return helps to sequester more carbon that offsetting the enhanced N2O emissions from the calcareous soil in the rotation system as it promotes reduction of more N2O to N2 in the wheat season.

Source Apportionment and Toxic Potency of PM2.5-Bound Polycyclic Aromatic Hydrocarbons (PAHs) at an Island in the Middle of Bohai Sea, China

Polycyclic aromatic hydrocarbons (PAHs) have attracted more attention because of their high atmospheric concentration and toxicity in recent decades. In this study, a total of 60 PM2.5 samples were collected from Beihuangcheng Island in Bohai Sea, China, from August 2017 to March 2018 for analyzing 16 congeners of PAHs (Σ16PAHs). Sources of PAHs were apportioned by a positive matrix factorization (PMF) model and the carcinogenic risk due to exposure to the PAHs was estimated by the toxicity equivalent of BaP (BaPeq). The results showed that the average concentration of Σ16PAHs was 35.3 ± 41.8 ng/m3. The maximum concentration of Σ16PAHs occurred in winter, followed by spring and autumn, and summer. The PMF modeling apportioned the PAHs into four sources, coal combustion, biomass burning, vehicle exhaust, and petroleum release, contributing 43.1%, 25.8%, 24.7%, and 6.39%, respectively. The average ΣBaPeq concentration was 2.32 ± 4.95 ng/m3 during the sampling period, and vehicle exhaust was the largest contributor. The finding indicates that more attention should be paid to reduce the emissions from coal combustion and vehicle exhaust because they were the largest contributors to the PAH concentration in PM2.5 and ΣBaPeq concentration, respectively.

Climate and ocean circulation in the aftermath of a Marinoan snowball Earth

Abstract. When a snowball Earth deglaciates through a very high atmospheric CO2 concentration, the resulting inflow of freshwater leads to a stably stratified ocean, and the strong greenhouse conditions drive the climate into a very warm state. Here, we use a coupled atmosphere–ocean general circulation model, applying different scenarios for the evolution of atmospheric CO2, to conduct the first simulation of the climate and the three-dimensional ocean circulation in the aftermath of the Marinoan snowball Earth. The simulations show that the strong freshwater stratification breaks up on a timescale of the order of 103 years, mostly independent of the applied CO2 scenario. This is driven by the upwelling of salty waters in high latitudes, mainly the Northern Hemisphere, where a strong circumpolar current dominates the circulation. In the warmest CO2 scenario, the simulated Marinoan supergreenhouse climate reaches a global mean surface temperature of about 30 ∘C under an atmospheric CO2 concentration of 15×103 parts per million by volume, which is a moderate temperature compared to previous estimates. Consequently, the thermal expansion of seawater causes a sea-level rise of only 8 m, with most of it occurring during the first 3000 years. Our results imply that the surface temperatures of that time were potentially not as threatening for early metazoa as previously assumed. Furthermore, the short destratification timescale found in this study implies that Marinoan cap dolostones accumulated during the deglacial period, given that they were deposited under the influence of a freshwater environment.