Organic Carbon Emissions Research Articles

Rapid decline in atmospheric organic carbon deposition in rural Beijing, North China between 2016 and 2020

Atmospheric deposition of dissolved organic carbon (DOC) is equivalent to the magnitude of riverine export of organic carbon (OC) to the oceans. Interpreting the fluctuations of DOC in precipitation is therefore essential in understanding the global carbon balance. This study measured DOC in 137 rain events collected from November 2016 to November 2020 at a rural site in agricultural areas of Beijing on the North China Plain. Concentrations of DOC ranged from 0.09 to 19.69 mg C L−1 with a volume weighted mean value of 2.76 ± 0.27 mg C L−1, which is comparable with those measured in North China a decade ago (3.0 ± 0.4 mg C L−1) and the global mean level (2.64 ± 2.04 mg C L−1). While differences in these values were small, their overall mean values were statistically different (p < 0.05). When classified via air mass back-trajectories, precipitation events with trajectories from south demonstrated higher DOC concentrations than those from north, matching with the spatial distribution of OC emission in the region. The annual precipitation DOC fluxes varied from 6.60 to 15.85 kg C ha−1 yr−1, with an average of 11.05 ± 3.83 kg C ha−1 yr−1 in this study. Both the annual mean concentrations and fluxes of precipitation DOC decreased by approximately 60% between 2017 and 2020, coinciding with the declining trend in OC emissions and aerosol OC concentrations due to the clean air actions. These unique data will allow for a better understanding of current status of rainwater DOC deposition on the global scale and will be critical for evaluating the impacts of future changes, e.g., replacing coal with natural gas, on atmospheric composition.

Water reuse as a strategy for mitigating atmospheric emissions and protecting water resources for the circularity of the swine production chain

High greenhouse gas emissions, high water demand, and waste with high pollution potential are critical points for waste management generated in animal production. With significant contributions in global emissions of air pollutants, sustainable practices for agriculture are fundamental to mitigate global climate change, besides ensuring protection to water resources, which is as critical as climate issues. Despite the importance of these issues, some gaps exist in the literature to develop practices capable of fostering water security and mitigation of greenhouse gas emissions. In this sense, the present study aimed to evaluate the impacts of reusing NO3− rich effluents inside the facilities for cleaning the swine houses and consequent atmospheric emissions of nitrous oxide (N2O) and methane (CH4). In swine manure, the generation of volatile fatty acids (VFA) was strongly influenced by temperature; a change in temperature from 10 to 18 °C increased by ten times the rate of VFA production, reflecting directly in methane emission and availability of organic carbon for the denitrification process. The effluent reuse practice, rich in nitrate, considering the organic carbon bioavailability in the pit storage, decreased methanogenic activity with a consequent VFA use as a bioavailable carbon source for denitrification, reducing greenhouse gas (GHG) emissions and consequently, the environmental impacts of swine production. In this way, the water reuse of 40% can mitigate up to 80% of GHG emission, with a minimum C/N ratio of 20, to ensure that at all temperatures the denitrifying process occurs efficiently since the carbon limitation negatively affected the N2O emission due to incomplete denitrification. Therefore, our results demonstrate the importance of this practice for swine sustainability and the capacity to adopt simple measures in favor of circularity in the swine production chain.

Aging behavior of microplastics affected DOM in riparian sediments: From the characteristics to bioavailability

Riparian zone is a hub for microplastics (MPs), and MPs accumulation also changes the function of the riparian zone (e.g., carbon pool) to pose a great threat to river ecosystems. Although it is known that MPs can be aged for changing their characteristic after accumulating in riparian sediment, the effect of MP aging behavior on sediment dissolved organic matter (DOM) bioavailability and carbon emission has not been elucidated. In this study, effects of pristine and aged MPs on the DOM characteristics and components were investigated in sediment. The results showed that pristine MPs increased DOM humification and promoted the formation of larger molecular weight components, thereby reducing DOM bioavailability by approximately 16~23% and inducing negative priming effect. However, inhibition of MPs on DOM bioavailability and the priming effect decreased with aging behavior. Mathematical models revealed that the fulvic acid-like substance of sediment DOM was the driven factor in the influence of sediment carbon stability. Further microbial analysis found that higher carbohydrate metabolism promoted DOM humification, thereby reducing CO2 emissions approximately by 19~26% after MPs accumulation. Thus, this study provided an integrated picture to understand the risk of MPs accumulation in sediment for a long term on terrestrial and aquatic ecosystems.

High concentrations of ice crystals in upper-tropospheric tropical clouds: is there a link to biomass and fossil fuel combustion?

Abstract. Eight years of upper-tropospheric (UT) ice crystal measurements with the backscatter cloud probe (BCP), installed on commercial aircraft operated as part of the In-Service Aircraft for a Global Observing System (IAGOS), have been analyzed to assess the frequency and characteristics of extreme ice crystal events (EIEs), defined in this study as encounters with clouds that have number concentrations exceeding 5000 L−1. A total of 3196 events, in clouds of horizontal extent ≥ 2.5 km, were identified during the period from December 2011 to March 2020 in the latitude band between 30∘ S and 30∘ N. Regions of anthropogenic sources of carbon monoxide, with particles that can alter cloud microphysics, were attributed to these EIEs in UT clouds using the SOFT-IO model. The evaluation of low- and upper-level kinematic variables from the European Centre for Medium-Range Weather Forecasts (ERA5) reanalysis, combined with spatial distributions of aerosol optical depth and regions of biomass burning, highlights the physical mechanisms by which the particles are lofted to flight levels in regions of deep convection. The maps of lightning frequency, derived from the World Wide Lightning Location Network (WWLLN), provide additional evidence of the role of deep convection in transporting aerosol particles, cloud hydrometeors and carbon monoxide to aircraft cruising altitudes. The evaluation of aerosol particle mass concentrations and composition from the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) contributes additional evidence for a link between regions of EIEs and surface emissions of dust, black carbon (BC), organic carbon (OC) and sulfate particles. Given the composition of the source aerosols and the role of deep convection in their transport to the UT, the sampled ice clouds likely originate from the homogeneous or heterogeneous freezing of droplets formed on these particles, as has been reported in previous studies. The results from this study, which have been obtained from a large sample of measurements, have ramifications related to satellite measurement validation, weather forecasting and climate change. In addition, over 2000 of the randomly sampled clouds had derived ice water contents larger than 1 g m−3, a concentration that is considered potentially hazardous to commercial aircraft operations.

A Comprehensive 2018-Based Vehicle Emission Inventory and Its Spatial-Temporal Characteristics in the Central Liaoning Urban Agglomeration, China.

Rapid economic expansion and urbanisation have seriously affected the atmospheric environmental quality of the Central Liaoning Urban Agglomeration (CLUA). This study aimed to establish a detailed vehicle emission inventory of the CLUA with a 3 km × 3 km gridded spatiotemporal distribution. A top-down methodology using vehicle kilometres travelled annually, emission factors, and activity data of each city was established. Carbon monoxide (CO), nitrogen oxides (NOx), sulfur dioxide (SO2), ammonia (NH3), volatile organic compounds (VOCs), particulate matter with an aerodynamic diameter less than 2.5 μm (PM2.5), particulate matter with an aerodynamic diameter less than 10 μm (PM10), Black Carbon (BC), and organic carbon (OC) emissions were 291.0, 221.8, 3.6, 2.2, 42.8, 9.3, 10.3, 5.2, and 1.6 Gg in 2018, respectively. The contribution of diesel heavy-duty trucks to NOx, SO2, PM2.5, PM10, BC, and OC emissions was greater than 54.5%, the largest contribution of all vehicles. Gasoline small passenger vehicles were the primary contributor to CO, VOC, and NH3 emissions, contributing 37.3%, 39.5%, and 75.3% of total emissions, respectively. For emission standards, Pre-China 1 vehicles were the largest contributor to CO and VOC emissions and China 3 vehicles contributed the largest amount of NOx, SO2, PM2.5, PM10, BC, and OC emissions. The spatial distribution of pollutants showed “obvious lines” and grids with high emissions were concentrated in expressways, national highways, and provincial highways. The temporal variation showed morning–evening peaks during diurnal variations, which was consistent with resident behaviour. This work can help us understand vehicular emission characteristics of the CLUA and provide basic data for air quality modelling. Future research should investigate traffic flow by vehicle types and emission factors at a local level, which will be helpful for transport management planning.

Existence and Formation Pathways of High- and Low-Maturity Elemental Carbon from Solid Fuel Combustion by a Time-Resolved Study.

Elemental carbon (EC) from various sources contains different sub-fractions with different properties; however, this variability poses several challenges for the accurate assessment of EC emission inventory. EC is defined using thermo-optical analysis (TOA), and its different fractions have different maturation and formation pathways. High- and low-maturity ECs have similar detection signals to those of Soot-EC and Char-EC in TOA. The emission characteristics of Soot-EC and Char-EC were affected by fuel composition and combustion temperatures. Biomass combustion generated more Char-EC than coal combustion, resulting in lower Soot-EC to Char-EC ratios. Soot-EC emissions always increased with an increasing temperature. Char-EC emissions increased with an increasing temperature at 300-900 °C in biomass combustion and decreased in coal combustion when the temperature was >600 °C, suggesting that the two ECs have different formation pathways. Time-resolved analyses of organic carbon (OC), EC, and polycyclic aromatic hydrocarbons showed that Char-EC was preferentially generated in the ignition stage with the rapid emission of OC through direct conversion of OC, whereas Soot-EC was preferentially generated during the flaming stage through gas-phase polymerization of small molecules generated from the decomposition of OC.

Changing Emissions Results in Changed PM2.5 Composition and Health Impacts

In the period of 2005 to 2016, multiple air pollution control regulations have entered into effect in the United States at both the Federal and state level. In addition, economic changes have also occurred primarily in the electricity generation sector that substantially changed the emissions from this sector. This combination of policy implementations and economics has led to substantial reductions in PM2.5, its major constituents, and source specific PM2.5 concentrations across the New York State, particularly those of sulfate, nitrate, and primary organic carbon. However, secondary organic carbon and spark-ignition vehicular emission contributions have increased. Related studies of changes in health outcomes, the excess rates of emergency department visits and hospitalizations for a variety of cardiovascular and respiratory diseases and respiratory infections have increased per unit mass of PM2.5. It appears that the increased toxicity per unit mass was due to the reduction in low toxicity constituents such that the remaining mass had greater impacts on public health.

Gasoline Direct Injection Engine Emissions of OC and EC: Laboratory Comparisons with Port Fuel Injection Engine

To better understand carbonaceous aerosol emissions from gasoline vehicles, a gasoline direct injection (GDI) vehicle with and without a gasoline particle filter (GPF) installed and a port fuel injection (PFI) vehicle were tested on a chassis dynamometer using standard emission drive cycles. Carbonaceous particles emitted from the vehicles were collected on quartz filters and analyzed using three different thermal optical protocols to assess the sensitivity of organic carbon (OC) and elemental carbon (EC) emission estimates to the methods, showing OC obtained by the IMPROVE and EC by the NIOSH protocol was the lowest. Compared to the PFI vehicle, the GDI vehicle had higher EC and OC emissions under cold-start cycles by 1415% and 46%, respectively. However, the OC emission from the PFI vehicle was higher than GDI during an aggressive driving cycle by 146%. By considering OC collected on a quartz filter behind a Teflon filter, the emissions from PFI vehicle were found to be more volatile than the GDI vehicle. This is consistent with the OC forming characteristics for GDI and PFI engines, which are pyrolyzed particles from incomplete combustion and incomplete volatilization of fuel droplets, respectively. Generally, the particle phase OC emissions from gasoline engines are more volatile than other sources (e.g., biomass burning), supported by the very low level of pyrolyzed organic carbon (POC) and small differences among protocols in the current study. Once the GDI vehicle was equipped with a GPF, the removal efficiency of EC was > 98%, but OC emissions could increase as a result of regeneration, suggesting that the effect of a GPF on total carbon emitted to the atmosphere needs further evaluation, especially considering the formation of secondary organic aerosol.

Effects of a barium-based additive on gaseous and particulate emissions of a diesel engine

The addition of barium-based additives is one of the main methods used to suppress smoke emissions in non-road diesel engines. Herein, a commercial barium-based additive was added to diesel fuel at the manufacturer's recommended concentration and used in a non-road four-cylinder supercharged diesel engine, without an after-treatment system, in bench experiments. Regulated emissions of the diesel engine were measured, volatile organic compounds (VOCs) and particulate matter (PM) were sampled. The carbonaceous fraction, water-soluble ions and inorganic elements in the PM were analyzed. Results indicated that the additive effectively reduced carbon monoxide (CO), hydrocarbon (HC) and smoke emissions from the engine. A 71% reduction in smoke was observed at the rated working condition, which was the maximum reduction of the three tested conditions. The additive produced a 36% reduction of VOCs at the rated working condition. The proportion of high carbon number hydrocarbons in the VOCs increased while the atmospheric reactivity of the VOCs decreased. The additive suppressed the concentration of organic carbon (OC) and elemental carbon (EC) emissions with a maximum reduction (40%) of total carbon achieved under the rated working condition. After the application of the additive, the concentration of water-soluble ions (Cl-, SO42‐, NO3‐, Na+, K+, Ca2+, NH4+) and elements (Fe, Mn, S, Ca, Ba) in the PM increased. A trend of increasing Barium content in the PM matched a similar trend of decreasing smoke.

Effect of ozonation on the biodegradability of urban wastewater treatment plant effluent

The present work aimed to study the effect of ozonation on the organic sum parameters linked to enhanced biodegradability. Laboratory experiments were conducted with the effluent of four Austrian urban wastewater treatment plants with low food to microorganism ratios and different matrix characteristics. Biochemical oxygen demand over 5 days (BOD5) was measured before ozonation and after application of different specific ozone doses (Dspec) (0.4, 0.6 and 0.8 g O3/g DOC). Other investigated organic parameters comprised chemical oxygen demand (COD), dissolved organic carbon (DOC), UV absorption at 254 nm (UV254), which are parameters that are applied in routine wastewater analysis. Carbamazepine and benzotriazole were measured as reference micropollutants. The results showed a dose-dependent increase in biological activity after ozonation; this increase was linked to the enhanced biodegradability of substances that are recalcitrant to biodegradation in conventional activated sludge treatment. The highest relative change was determined for BOD5, which already occurred between 0 and 0.4 g O3/g DOC for all samples. Increasing the Dspec to 0.6 and 0.8 g O3/g DOC resulted in a less pronounced increase. DOC was not substantially decreased after ozonation, which was consistent with a low reported degree of mineralization, while partial oxidation led to a quantifiable decrease in COD (7 to 17%). Delta UV254 and the decline in specific UV absorption after ozonation clearly correlated with Dspec. In contrast, for COD and biodegradable DOC (BDOC), a clear dose-response pattern was identified only after exposure to BOD5 measurement. Indications for improved biodegradability were further supported by the rise in the BOD5/COD ratio. The results indicated that subsequent biological processes have a higher degradation potential after ozonation. The further reduction in biodegradable organic carbon emission by the combination of ozonation and biological post treatment represents another step towards sustainable water resource management in addition to micropollutant abatement.

Проблеми та можливості моделювання потенціалу секвестрації діоксиду карбону грунтами України

The article examines approaches to modelling carbon dioxide sequestration by soils at different scale levels and describes a number of problems encountered in this process. The main problems in the modelling of organic carbon reserves for the territory of Ukraine have been identified, among which: lack of high-resolution data (hard to access), including types of land use; need for harmonization of existing data; the need for predicative modelling of indicators (clay and organic carbon content) for areas where data are not available; significant amounts of machine time for actual modelling. The need for open access to archived data (technical reports) from large-scale soil surveys 1957-1990 is highlighted. Also, the need to access large-scale topographic data as in the form of scanned topographic maps M 1:10000 and vectorized isolines are substantiated. It is shown that calculations of areas based on rasters in the geographical coordinate system to ensure the same pixel size, regardless of the location within Ukraine, it is proposed to use the “Ukraine Albers conic equal area” projection based on the Datum Pulkovo 1942 for which the error in the lengths of the lines is only 0.1%. Within areas can be used as a proposed projection, as well as precise Gauss-Kruger projections (EPSG 28404-28407, 5565-5583). In this case, it is necessary to take into account the likelihood of finding individual areas in several of the listed zones. It is demonstrated that simulation allows to establish territories in which even the best practices of management do not provide neutralization of emission of organic carbon from soils. However, it is necessary to introduce a priority introduction of adaptive management of the soil resources of agro-landscapes that will contribute to carbon sequestration or minimization of its emission.

Soil burial reduces decomposition and offsets erosion-induced soil carbon losses in the Indian Himalaya.

The extent to which soil erosion is a net source or sink of carbon globally remains unresolved but has the potential to play a key role in determining the magnitude of CO2 emissions from land-use change in rapidly eroding landscapes. The effects of soil erosion on carbon storage in low-input agricultural systems, in acknowledged global soil erosion hotspots in developing countries, are especially poorly understood. Working in one such hotspot, the Indian Himalaya, we measured and modelled field-scale soil budgets, to quantify erosion-induced changes in soil carbon storage. In addition, we used long-term (1-year) incubations of separate and mixed soil horizons to better understand the mechanisms controlling erosion-induced changes in soil carbon cycling. We demonstrate that high rates of soil erosion did not promote a net carbon loss to the atmosphere at the field scale. Furthermore, our experiments showed that rates of decomposition in the organic matter-rich subsoil layers in depositional areas were lower per unit of soil carbon than from other landscape positions; however, these rates could be increased by mixing with topsoils. The results indicate that, the burial of soil carbon, and separation from fresh carbon inputs, led to reduced rates of decomposition offsetting potential carbon losses during soil erosion and transport within the cultivated fields. We conclude that the high rates of erosion experienced in these Himalayan soils do not, in isolation, drive substantial emissions of organic carbon, and there is the potential to promote carbon storage through sustainable agricultural practice.

Volatile Chemical Product Enhancements to Criteria Pollutants in the United States.

Volatile chemical products (VCPs) are a significant source of reactive organic carbon emissions in the United States with a substantial fraction (>20% by mass) serving as secondary organic aerosol (SOA) precursors. Here, we incorporate a new nationwide VCP inventory into the Community Multiscale Air Quality (CMAQ) model with VCP-specific updates to better model air quality impacts. Model results indicate that VCPs mostly enhance anthropogenic SOA in densely populated areas with population-weighted annual average SOA increasing 15-30% in Southern California and New York City due to VCP emissions (contribution of 0.2-0.5 μg m-3). Annually, VCP emissions enhance total population-weighted PM2.5 by ∼5% in California, ∼3% in New York, New Jersey, and Connecticut, and 1-2% in most other states. While the maximum daily 8 h ozone enhancements from VCP emissions are more modest, their influence can cause a several ppb increase on select days in major cities. Printing Inks, Cleaning Products, and Paints and Coatings product use categories contribute ∼75% to the modeled VCP-derived SOA and Cleaning Products, Paints and Coatings, and Personal Care Products contribute ∼81% to the modeled VCP-derived ozone. Overall, VCPs enhance multiple criteria pollutants throughout the United States with the largest impacts in urban cores.

Urban residential energy switching in China between 1980 and 2014 prevents 2.2 million premature deaths

Urban residential energy switching in China between 1980 and 2014 prevents 2.2 million premature deaths

Biochar and its manure-based feedstock have divergent effects on soil organic carbon and greenhouse gas emissions in croplands

Applying organic amendments to soil can increase soil organic carbon (SOC) storage and reduce greenhouse gas (GHG) emissions generated by agriculture, helping to mitigate climate change. However, it is necessary to determine which type of amendment produces the most desirable results. We conducted a 3-y field study comparing one-time addition of manure compost and its biochar derivative to a control to assess their effects on SOC and GHG emissions at ten annually cropped sites in central Alberta, Canada. Manure compost and biochar were applied at equivalent carbon rates (7 Mg ha−1) and tilled into the surface 10 cm of soil. Two years post-treatment, biochar addition increased surface (0–10 cm) SOC by 12 and 10 Mg ha−1 relative to the control and manure addition, respectively. Therefore, biochar addition led to the sequestration of SOC at a rate of 2.5 Mg ha−1 y−1 relative to the control. No treatment effect on deeper (10–100 cm) or cumulative SOC was found. In 2018 and 2019, manure addition increased cumulative GHG (sum of CO2, CH4, and N2O) emissions by 33%, on average, due to greater CO2 emissions relative to both the control and biochar addition. In contrast, in 2020, biochar addition reduced cumulative GHG emissions by an average of 21% due to lower CO2 emissions relative to both the control and manure addition. Our study shows that the application of biochar, rather than its manure compost feedstock, increased surface SOC sequestration and had either no effect on (first two years) or reduced GHG emissions (year three) relative to the control. We recommend that policy and carbon sequestration initiatives focus on optimizing biochar production-application systems to fully realize the potential of biochar application as a viable climate change mitigation practice in agriculture.

Characteristics of fine carbonaceous aerosols in Wuhai, a resource-based city in Northern China:Insights from energy efficiency and population density

As one of the predominant compositions of PM2.5 (particulate matter with aerodynamic diameter ≤2.5 μm), carbonaceous aerosols not only have adverse effects on air quality, but also can affect climate change. Although there are extensive recent studies on carbonaceous aerosols, comprehensive studies on their socioeconomic influencing factors in a resource-based city are relatively limited. In this study, the spatial-temporal variations of organic carbon (OC), elemental carbon (EC), and secondary organic carbon (SOC) were investigated in January, July, and October in 2015 and April in 2016 in Wuhai and its surrounding areas. The population distribution and industry layout have led to the uneven spatial-temporal distribution of carbonaceous aerosols. The concentrations of carbonaceous aerosols were higher in winter due to the unfavorable meteorology and the increased emissions from heating. The SOC is a significant contributor to OC in the cold season (52.0% for January). Primary carbonaceous aerosols pollution is higher in the industrial sites of resource-based cities, whereas the SOC makes a significant contribution in the residential sites. The results of backward-trajectory and concentration-weighted trajectory analysis suggest that the local emissions and short-range atmospheric transport from nearby areas have a significant impact on PM2.5 and carbonaceous aerosols. A strong correlation between population density and OC/EC ratio was found, indicating that the megacities with high population density have a higher SOC contribution than the resource-based cities. Resource-based cities are characterized by high level of primary OC emissions, whereas cities with high energy efficiency have a more significant SOC contribution. These results provide a more comprehensive understanding of carbonaceous aerosols in a resource-based city.

Toward a cleaner domestic wood heating by the optimization of firewood stoves?

This study aims to determine the evolution of many pollutants, especially the particles and their precursors, by four generations of wood-burning domestic heating appliances between 2000 and 2015. As the particles emissions issue remains relevant, the second part of this work concerns the simulation of the firewood fleet emissions evolution. Many characteristics of the particles were measured: mass, number, size distribution, Organic and Elemental Carbon composition, SEM imaging … We also followed the emissions of NOx, Total Volatile Organic Compounds (TVOC) and Polycyclic Aromatic Hydrocarbons (PAHs). The particles emissions, in mass or number, has decreased drastically overall size fractions. All the technologies that increase the turbulence in the combustion chamber increase impaction mechanisms and therefore limit the flying ashes/coal. The secondary airflow introduction reduces the amount of pollutants emitted. Organic Carbon emissions decrease by the chamber insulation, sealing and the design of the device. Optimizing combustion drastically reduces the amount of PAHs emitted, but the emissions profile remains stable. The simulation results are that with the actual firewood stove renewal rate, the emissions will considerably decrease in the next decade: −14% for the TVOC, −50% for the PAH16, -42% for the TSP and −26% for the OC.

Evaluation and intercomparison of wildfire smoke forecasts from multiple modeling systems for the 2019 Williams Flats fire

Abstract. Wildfire smoke is one of the most significant concerns of human and environmental health, associated with its substantial impacts on air quality, weather, and climate. However, biomass burning emissions and smoke remain among the largest sources of uncertainties in air quality forecasts. In this study, we evaluate the smoke emissions and plume forecasts from 12 state-of-the-art air quality forecasting systems during the Williams Flats fire in Washington State, US, August 2019, which was intensively observed during the Fire Influence on Regional to Global Environments and Air Quality (FIREX-AQ) field campaign. Model forecasts with lead times within 1 d are intercompared under the same framework based on observations from multiple platforms to reveal their performance regarding fire emissions, aerosol optical depth (AOD), surface PM2.5, plume injection, and surface PM2.5 to AOD ratio. The comparison of smoke organic carbon (OC) emissions suggests a large range of daily totals among the models, with a factor of 20 to 50. Limited representations of the diurnal patterns and day-to-day variations of emissions highlight the need to incorporate new methodologies to predict the temporal evolution and reduce uncertainty of smoke emission estimates. The evaluation of smoke AOD (sAOD) forecasts suggests overall underpredictions in both the magnitude and smoke plume area for nearly all models, although the high-resolution models have a better representation of the fine-scale structures of smoke plumes. The models driven by fire radiative power (FRP)-based fire emissions or assimilating satellite AOD data generally outperform the others. Additionally, limitations of the persistence assumption used when predicting smoke emissions are revealed by substantial underpredictions of sAOD on 8 August 2019, mainly over the transported smoke plumes, owing to the underestimated emissions on 7 August. In contrast, the surface smoke PM2.5 (sPM2.5) forecasts show both positive and negative overall biases for these models, with most members presenting more considerable diurnal variations of sPM2.5. Overpredictions of sPM2.5 are found for the models driven by FRP-based emissions during nighttime, suggesting the necessity to improve vertical emission allocation within and above the planetary boundary layer (PBL). Smoke injection heights are further evaluated using the NASA Langley Research Center's Differential Absorption High Spectral Resolution Lidar (DIAL-HSRL) data collected during the flight observations. As the fire became stronger over 3–8 August, the plume height became deeper, with a day-to-day range of about 2–9 km a.g.l. However, narrower ranges are found for all models, with a tendency of overpredicting the plume heights for the shallower injection transects and underpredicting for the days showing deeper injections. The misrepresented plume injection heights lead to inaccurate vertical plume allocations along the transects corresponding to transported smoke that is 1 d old. Discrepancies in model performance for surface PM2.5 and AOD are further suggested by the evaluation of their ratio, which cannot be compensated for by solely adjusting the smoke emissions but are more attributable to model representations of plume injections, besides other possible factors including the evolution of PBL depths and aerosol optical property assumptions. By consolidating multiple forecast systems, these results provide strategic insight on pathways to improve smoke forecasts.

Changes of lake organic carbon sinks from closed basins since the Last Glacial Maximum and quantitative evaluation of human impacts

BackgroundClosed basins occupy 21% of the world’s land area and can substantially affect global carbon budgets. Conventional understanding suggests that the terminal areas of closed basins collect water and carbon from throughout the entire basin, and changes in lake organic carbon sinks are indicative of basin-wide organic carbon storages. However, this hypothesis lacks regional and global validation. Here, we first validate the depositional process of organic carbon in a typical closed-basin region of northwest China using organic geochemical proxies of both soil and lake sediments. Then we estimate the organic carbon sinks and human impacts in extant closed-basin lakes since the Last Glacial Maximum (LGM).ResultsResults show that 80.56 Pg organic carbon is stored in extant closed-basin lakes mainly found in the northern mid-latitudes. Carbon accumulation rates vary from 17.54 g C m−2 yr−1 during modern times, 6.36 g C m−2 yr−1 during the mid-Holocene and 2.25 g C m−2 yr−1 during the LGM. Then, we evaluated the influence by human activities during the late Holocene (in the past three thousand years). The ratio of human impacts on lake organic carbon storage in above closed basins is estimated to be 22.79%, and human-induced soil organic carbon emissions in the past three thousand years amounted to 207 Pg.ConclusionsWhile the magnitude of carbon storage is not comparable to those in peatland, vegetation and soil, lake organic carbon sinks from closed basins are significant to long-term terrestrial carbon budget and contain information of climate change and human impact from the whole basins. These observations improve our understanding of carbon sinks in closed basins at various time scales, and provide a basis for the future mitigation policies to global climate change.

Effects of long-term no tillage and straw return on greenhouse gas emissions and crop yields from a rice-wheat system in central China

Extensive attention has been attracted to no tillage and straw return due to its carbon sequestration and greenhouse gas (GHG) emissions alteration properties. However, the impacts of perceived long-term no tillage and straw return on GHG emissions and crop yields in the rice-wheat system remain unclear. A six-year field experiment was conducted to investigate the temporal impacts of no tillage and straw return on soil organic carbon (SOC), CH4 and N2O emissions, and crop yields. Significant effects of no tillage and straw return on SOC were observed after 5 years of the experiment. The influence of no tillage and straw return on N2O and CH4 emissions and crop yields presented temporal disparities. No tillage significantly increased N2O emission by 28.9%, but reduced CH4 emission by 18.3% during 6-year field experiment relative to conventional tillage. Moreover, no tillage had no significant effect on the annual crop yield. By contrast, straw return remarkably increased N2O emissions, CH4 emissions and annual crop yield by 41.2%, 47.5% and 4.1% over the 6-year field experiment relative to straw removal. Besides, no tillage significantly decreased net global warming potential (GWP) by 27.7%, and had no significant effect on net ecosystem economic budget (NEEB). Inversely, straw return markedly increased the net GWP by 46.2% and the NEEB by 3.4%. Together, these results showed that agricultural strategy of long-term no tillage with straw return is likely to result in low GHG emissions and high crop yields and economic profit in rice-wheat system, suggesting the potential benefit of no tillage with straw return for GHG mitigation and food security.