Distribution Of Black Carbon Research Articles

Numerical prediction of the distribution of black carbon in a street canyon using a semi-Lagrangian finite element formulation

We present a procedure for coupling the fluid and transport equations to model the distribution of a pollutant in a street canyon, in this case, black carbon (BC). The fluid flow is calculated with a stabilized finite element method using the Quasi-Static Variational Multiscale (QS-VMS) technique. For the temperature and pollutant transport we use a semi-Lagrangian procedure, based on the Particle Finite Element Method (PFEM) combined with an Eulerian method based on a Finite Increment Calculus (FIC) formulation. Both methods are implemented on the open-source KRATOS Multiphysics platform. The coupled numerical formulation is applied to the prediction of the transport of BC in a street canyon, which can be a useful tool to lessen the impact of pollutants on pedestrians. Two test cases have been studied: a 2D simplified case and a more complex 3D one. The main goal of this study is to propose a useful tool to study the effect of pollution on pedestrians in a street-level scale. Good comparison with experimental results is obtained.

Photochemical Transformation and Catalytic Activity of Dissolved Black Nitrogen Released from Environmental Black Carbon.

Biomass combustion results in the formation and wide distribution of black carbon (BC) in soils, wherein the dissolved fractions are among the most active components. Although the presence of dissolved black nitrogen (DBN) in BC has been identified, its environmental behavior and implication are not understood. This study investigated the photochemical transformation and catalytic activity of DBN under simulated solar irradiation. DBN is more easily transformed than dissolved BC due to its photoactive heteroaromatic N structure, and the half-life of DBN produced at 500 °C (8.6 h) is two times shorter than that of the dissolved BC counterpart (23 h). Meanwhile, solar irradiation is favorable for the homoaggregation of DBN. During irradiation, DBN generates not only reactive oxygen species (e.g., 1O2, O2-, and •OH) but also reactive nitrogen species (mainly •ON), which account for its higher photocatalytic degradation of bisphenol A than dissolved BC. These findings shed new light on the impact of heteroatoms on the phototransformation and activity of BC as well as cycling of N in terrestrial systems.

Improved Simulations of Global Black Carbon Distributions by Modifying Wet Scavenging Processes in Convective and Mixed‐Phase Clouds

AbstractIn‐cloud wet scavenging dominates the wet removal of aerosols in the atmosphere, but is not well represented in climate models. Aircraft measurements of black carbon (BC) concentrations suggest that models commonly overestimate BC concentrations in the upper troposphere of the tropics by more than one order of magnitude but underestimate BC burdens in polar latitudes. In this study, we improved the in‐cloud wet scavenging parameterizations for convective clouds and mixed‐phase clouds to better characterize BC abundances in the remote atmosphere (remote oceans and polar regions) with a global model, CAM5‐ATRAS2. The modified wet scavenging processes in the model achieved a more realistic simulation of BC concentrations over both the tropics and the Arctic. The new, unified scheme for vertical transport and wet removal during deep convection generally reproduced the observed low mixing ratios (about 0.1 ng kg−1) of BC in the middle and upper troposphere over the tropics, and the Wegener–Bergeron–Findeisen process (WBF) lowered the wet removal efficiency of BC from mixed‐phase clouds and consequently increased BC burdens in the Arctic by about a factor of 2. The BC direct radiative forcings increased by 20% globally (from 0.26 to 0.31 W m−2), and more importantly by a factor of 2 in the Arctic (from 0.09 to 0.18 W m−2). Our results indicated that good agreement between modeled and observed BC concentrations could be obtained in the remote atmosphere without requiring the relatively short global BC lifetime (∼4 days) suggested by previous studies.

Observations of Emissions and the Influence of Meteorological Conditions during Wildfires: A Case Study in the USA, Brazil, and Australia during the 2018/19 Period

Wildfires can have rapid and long-term effects on air quality, human health, climate change, and the environment. Smoke from large wildfires can travel long distances and have a harmful effect on human health, the environment, and climate in other areas. More recently, in 2018–2019 there have been many large fires. This study focused on the wildfires that occurred in the United States of America (USA), Brazil, and Australia using Cloud-Aerosol Lidar with Orthogonal Polarisation (CALIOP) and a TROPOspheric Monitoring Instrument (TROPOMI). Specifically, we analyzed the spatial-temporal distribution of black carbon (BC) and carbon monoxide (CO) and the vertical distribution of smoke. Based on the results, the highest detection of smoke (~14 km) was observed in Brazil; meanwhile, Australia showed the largest BC column burden of ~1.5 mg/m2. The meteorological conditions were similar for all sites during the fires. Moderate temperatures (between 32 and 42 °C) and relative humidity (30–50%) were observed, which resulted in drier conditions favorable for the burning of fires. However, the number of active fires was different for each site, with Brazil having 13 times more active fires than the USA and five times more than the number of active fires in Australia. However, the high number of active fires did not translate to higher atmospheric constituent emissions. Overall, this work provides a better understanding of wildfire behavior and the role of meteorological conditions in emissions at various sites.

The black carbon content variations in the Arctic region during 2011 - 2018

Data on black carbon (BC) concentrations obtained from the board of research vessels (R/V), “Acad. Mstislav Keldysh”, “Acad. M. A. Lavrentyev” and “Prof. Molchanov” in 2011–2018. They were used to study the quantitative distribution of black carbon in the driving air layer over the seas of the Russian Arctic in the summer-autumn period and to determine its main source regions. Variations in the BC content in the near water layer of the atmosphere at the North Pole, in the Norwegian, Barents, Kara, East Siberian Seas and the Laptev Sea are obtained. As a result of 12 marine expeditions in the summer-autumn period of 2011 - 2018 the BC concentration in the atmospheric drive layer in the Arctic was mainly at the background level and averaged 47 ng/m3 (9-95 ng/m3). An increase in the BC concentration by several times, as shown by trajectory analysis, occurs occasionally upon receipt of air masses from the mainland, from areas of associated gas combustion. Low BC values were observed when air masses passed over the water surface from the northern regions of the Arctic. The BC concentration above the water surface depends on the state of the atmosphere in the region of soot sources on the mainland.

Concentration and Isotopic Composition of Methane, Associated Gases, and Black Carbon over Russian Arctic Seas (Shipborne Measurements)

In Russian Arctic seas, observations of surface methane concentrations (CH4), ozone, nitrogen and carbon oxides, as well as the content of $${{\delta }^{{13}}}{{{\text{C}}}_{{{\text{C}}{{{\text{H}}}_{4}}}}}$$ isotope and black carbon (BC, soot aerosol), were carried out from onboard of the R/V Academician Mstislav Keldysh. The areas of local methane releasing from bottom sediments were investigated. It was shown that the studied methane releasing on the Arctic shelf are of a local nature and, on the whole, insignificantly affect the composition of the atmosphere in the region. The average concentration of methane in the surface air in the Arctic seas is mainly determined by large-scale processes of air mass transfer. An analysis of the distribution of black carbon along the route of the vessel was carried out. It was found that the excess in the concentration of black carbon over the background values is observed occasionally during advection of air masses from the mainland and from the areas of associated gases burning and forest fires. The effect of emissions from a ship’s chimney on the data obtained was analyzed.

Efficient Vertical Transport of Black Carbon in the Planetary Boundary Layer

AbstractVertical distribution of black carbon (BC) determines the layer where its heating impacts exert. This study presents continuous and simultaneous measurements at surface and on a mountain site above the wintertime planetary boundary layer influenced by uplifted surface anthropogenic emissions. BC was observed efficiently transported upwards by daytime convective mixing. However, this vertical transport was less for other particulate masses. An about twofold higher BC mass fraction was thus present at mountain than surface, hereby a lowered single‐scattering albedo (SSA) by 0.06. This may be caused by the evaporative loss of condensed semivolatile materials, prevailing the secondary particulate formation, in a cleaner environment containing less precursors. The elevated BC mass corresponded with the most intensive solar radiation at midday, wielding more heating impacts over the planetary boundary layer (PBL). This phenomenon may apply to other remote regions where a reduced SSA will introduce more positive radiative effects.

Concentrations and Size Distributions of Black Carbon in the Surface Snow of Eastern Antarctica in 2011

AbstractKnowledge of black carbon (BC) concentrations and size distributions within surface snow in Antarctica is limited. However, these measurements are important to understanding global aerosol transport from combustion sources, and BC contributes to positive radiative forcing. This study analyzed the concentrations and size distributions of BC and inorganic ions in snow samples collected at the Syowa station in Antarctica from April to December 2011 and along a traverse route to an inland (Mizuho) station. The BC size distributions in snow were bimodal with mass median diameters of ~140 and ~690 nm. We also estimated the mass median diameter from unimodal distributions and found smaller diameters than were reported by other studies. The mass concentrations of BC in snow were higher in inland samples than in Syowa samples. Among Syowa samples, the BC concentrations in December (2117.3 ng L−1 on average) were higher than in other periods (288.2 ng L−1 on average). The December samples experienced ambient temperatures above 0 °C, and the atmospheric BC concentrations did not increase simultaneously. Inorganic ions originated from the ocean and decreased with increasing distance from the coastal area. We conclude that the BC concentrations in surface snow increased mainly by postdeposition processes through the loss of water mass due to melting, evaporation, and sublimation. Our study is the first to report detailed BC concentrations and size distributions in eastern Antarctica, and the results will help to evaluate BC global transport, the snow albedo estimations in this region, and the climate impacts of BC.

Visualizing the distribution of black carbon's electron storage capacity using silver

We have developed a method that combines chemical reduction, silver tagging, and electron microscopy (EM) for visualizing the electron storage capacity (ESC) of black carbon (BC). ESC is a BC's capacity to store and reversibly exchange electrons with abiotic and microbial agents, processes that are relevant to biochemistry, greenhouse gas production, contaminant fate, and remediation. In addition to the amount of electrons BC can store, the locations and spatial distribution of ESC on and inside biochar are critical for understanding the bioaccessibility of ESC and the kinetics of redox reactions involving BC. To locate the ESC in a BC particle, we fully reduced a BC, removed excess reductant, and applied silver ion (Ag+) as a tagging agent that diffused into BC to react with functional groups where electrons were stored (i.e., ESC) to form silver nanoparticles (nAg). The nAg deposited on and inside BC were then imaged using multiple EM techniques to visualize the locations and distribution of the ESC. The method is a new and potentially useful tool for investigating ESC production and for elucidating BC-mediated redox transformation.•Novel method to probe and assess the distribution of ESC on/within BC.•Visual confirmation of significant ESC both on the surface and in the interior of BC.•A new method to incorporate silver or other redox-sensitive elements into a carbon medium.

Interdecadal variation in aerosol optical properties and their relationships to meteorological parameters over northeast China from 1980 to 2017

Northeast China has undergone rapid urbanisation with increased anthropogenic emissions, and the types and absorption properties of aerosols may affect regional climate change. MERRA-2 (Modern-Era Retrospective analysis for Research and Applications, version 2) distributions of aerosol optical depth (AOD), Ångström exponent (AE), and absorption aerosol optical depth (AAOD) from 1980 to 2017 was studied to estimate the climatology of aerosol optical properties over Northeast China. The highest AOD and AAOD occurred in Liaoning Province range from 0.3 to 0.4 and 0.02–0.03, respectively. The spacial distribution of black carbon (BC) AOD was similar to AAOD with maximum value in Liaoning province about 0.04 related to the emission sources and human activities. The seasonal interdecadal distribution indicated larger dust (DU) AOD in Liaoning (0.12) and organic carbon (OC) AOD in Heilongjiang (0.18). The contribution of SO4 to total AOD was significant in autumn and winter, and BC particles contributed 70% to total AAOD in all seasons. The decadal change in AOD was positive for 2000–2009 (0.2/decadal) due to the increased dust events happening in spring. The positive correlation between AOD and relative humidity (RH) at surface was about 0.4–0.6; the negative correlation between AOD and surface wind speed (WS) (−0.6), planetary boundary layer height (PBLH) (−0.2 to −0.6), sea level pressure (SLP) (−0.2) was found over the study period. This study’s findings enable more comprehensive understanding of the distribution of aerosols optical properties and regional climatology in Northeast China.

Polycyclic aromatic hydrocarbons and heavy metals in urban environments: Concentrations and joint risks in surface soils with diverse land uses

AbstractAlthough polycyclic aromatic hydrocarbons (PAHs) and heavy metals (HMs) are abundant around cities, few researchers have studied the complex concentrations and joint risks of these pollutants in urban surface soils containing diverse land uses. We collected 69 urban surface soil samples from roadside districts, green belts, public green space, commercial districts, and residential district in urban areas of Nanjing, China to determine the concentrations, distributions, deposition patterns, and joint risks of PAH and HM contaminants. No significant differences were found among the five studied land uses, but a wide range of PAH levels were found in these land uses, as these diverse land uses have similar PAH pollution sources. As these areas persistently generate high PAH levels by gasoline/diesel engine or coal combustion, the PAH distribution characteristics indicated that commercial centers or city centers are the most heavily contaminated sites. The distributions of black carbon and HMs, except for Pb, were found to be significantly correlated. Except for Cd and As, HM levels among diverse land uses also showed no significant differences, possibly stemming from the non‐point source pollution of these metals in the study areas. Factor analysis showed that 46.2% of the elevated pollutant concentrations resulted from combustion processes, 24.3% were caused by natural background fluctuations, and 11.9% resulted from non‐combustion processes. The studied PAHs and As presented low carcinogenic risks. Cd, Cu, Pb, and Zn depicted acceptable total non‐carcinogenic risks in all land uses; however, the risks associated with these HMs possessed detailed differences.

Assessing Spatio-Temporal Variability of Wildfires and their Impact on Sub-Saharan Ecosystems and Air Quality Using Multisource Remotely Sensed Data and Trend Analysis

Globally, wildfires are considered the most commonly occurring disasters, resulting from natural and anthropogenic ignition sources. Wildfires consist of burning standing biomass at erratic degrees of intensity, severity, and frequency. Consequently, wildfires generate large amounts of smoke and other toxic pollutants that have devastating impacts on ambient air quality and human health. There is, therefore, a need for a comprehensive study that characterizes land–atmosphere interactions with regard to wildfires, critical for understanding the interrelated and multidimensional impacts of wildfires. Current studies have a limited scope and a narrow focus, usually only focusing on one aspect of wildfire impacts, such as air quality without simultaneously considering the impacts on land surface changes and vice versa. In this study, we use several multisource data to determine the spatial distribution, frequency, disturbance characteristics of and variability and distribution of pollutants emitted by wildfires. The specific objectives were to (1) study the sources of wildfires and the period they are prevalent in sub-Saharan Africa over a 9 year period, i.e., 2007–2016, (2) estimate the seasonal disturbance of wildfires on various vegetation types, (3) determine the spatial distribution of black carbon (BC), carbon monoxide (CO) and smoke, and (4) determine the vertical height distribution of smoke. The results show largest burned areas in December–January–February (DJF), June–July–August (JJA) and September–October–November (SON) seasons, and reciprocal high emissions of BC, CO, and smoke, as observed by Modern-Era Retrospective Analysis for Research and Applications version 2 (MERRA-2) and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO). In addition, the results reveal an increasing trend in the magnitude of BC, and CO concentration driven by meteorological conditions such as low precipitation, low relative humidity, and low latent heat flux. Overall, this study demonstrates the value of multisource remotely sensed data in characterising long-term wildfire patterns and associated emissions. The results in this study are critical for informing better regional fire management and air quality control strategies to preserve endangered species and habitats, promote sustainable land management, and reduce greenhouse gases (GHG) emissions.

Chemical and source characterization of PM2.5 in summertime in severely polluted Lahore, Pakistan

Abstract Lahore is considered the most polluted city in Pakistan with high levels of atmospheric particulate matter. The PM2.5 chemical composition and sources in Lahore were investigated in this study in an effort to effectively mitigate the pollution of PM2.5 in Lahore. In the month of July 2018, the day and night samples of PM2.5 in Lahore were collected and analyzed. Principal component analysis (PCA), concentration weighted trajectory (CWT) calculation and analysis of the spatial distribution of black carbon in Lahore obtained from MERRA-2 (Modern-Era Retrospective Analysis for Research and Applications, Version 2) reanalysis data were employed to identify the sources and contributing regions of PM2.5. The fuel consumption situation in Pakistan was also examined to further identify the major contributing sectors to air pollution. The most abundant species in the identified mass of PM2.5 were carbonaceous compounds, followed by ionic species such as SO42−, NO3−, Cl− and NH4+. Although secondary organic carbon showed a high percentage in OC (47%), primary organic carbon was still dominant in OC in Lahore. PM2.5 showed no correlation with meteorological parameters. Based on the CWT calculation and black carbon spatial distribution, local emission sources were the main sources of air pollution in Lahore, with an additional contribution from the western states of India. Overall, primary emissions from local sources showed a dominant contribution to PM2.5 pollution and controlling the emissions from industry, transportation, and power plants would show immediate effects for mitigating PM2.5 in Lahore. Capsule Comprehensive analyses of PM2.5 concentration and composition, meteorological conditions, PM2.5 sources, and consumption status of fossil fuel demonstrated the affecting factors of PM2.5 pollution in Lahore, Pakistan.

Impact of mixing state on aerosol optical properties during severe wildfires over the Euro-Mediterranean region

The impact of mixing state of particles from biomass burning on aerosol optical properties (aerosol optical depth (AOD) and single-scattering albedo (SSA)) is studied over the Euro- Mediterranean region during the severe fire event in the Balkans between 20 and 31 July 2007, also characterized by high dust concentrations. When the mixing state is resolved in chemistry-transport models, chemical compounds are grouped for computational reasons, and internal mixing is assumed within each group. Up to six groups are defined here (dust, black carbon, two inorganic groups and two organic groups). The influence of different grouping assumptions is studied here and compared to the influence of the distribution of black carbon (BC) in particles (“pure homogeneous” representation and “core-shell” one), and the influence of modeling the water absorbed by both inorganic and organic compounds. The comparisons of simulated AODs to observations from the surface network AERONET show that AOD is slightly underestimated when aerosol compounds are assumed to be externally mixed and slightly overestimated when they are assumed to be internally mixed. The mixing state of dust with other compounds, as well as the distribution of BC in particles, strongly influence the optical properties. The impact of the mixing state on AOD is higher than the impact of the distribution of BC in particles, reaching 8–12% on average over the fire regions and 16% in the fire plume. Analysis related to the impact of particle mixing state and BC distribution on SSA shows results similar to AOD. The impact of the mixing state on SSA can reach −8.5% over the fire regions and it is higher than the impact of the BC representation, which is lower than 2%. At the location of fires, water absorbed by inorganics and organics is shown to influence the AOD by about 2%, which is in the lower range of the influence of water on AOD over the region (between 0 and 40%). This low influence of water on AOD during fire is due to assumptions made in the modelling, where most of secondary organic aerosols formed during fires are assumed to be hydrophobic.

Assessment of absorbing aerosols on austral spring snow albedo reduction by several basins in the Central Andes of Chile from daily satellite observations (2000–2016) and a case study with the WRF-Chem model

Changes in snow albedo (SA) on the Limari, Choapa, Aconcagua and Maipo basins of the Central Andes of Chile (CAC) are associated with the possible deposition of light-absorbing particles in the austral spring. We correlate SA with daily data of snow cover, aerosol optical depth (AOD) and land surface temperature (LST) available from the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard the NASA Terra satellite between 2000 and 2016, and other derived parameters such as days after albedo (DAS) and snow precipitation (SP). We used satellite pixels with 100% snow cover to obtain monthly average value of SA, LST, AOD, DAS and SP from September to November performing multiple regression analysis. We show that in Maipo, after considering LST, AOD represents an important role in changes induced to SA. The multiple regression model illustrates that AOD increases can reduce the SA during spring months by 13.59, 0.01, 0.77 and 3.8% in Limari, Choapa, Aconcagua and Maipo, respectively. In addition, we used a numerical prediction Weather Research and Forecasting model coupled with Chemistry (WRF-Chem), showing that the black carbon distribution and average daily AOD are associated with the SA decrease of 0.15 in the Maipo basin between September 29 and 30, 2016. The WRF-Chem output showed aerosols are transported mainly with dominating westerly winds to the Limari and Maipo basins. Our results further suggest that SA decrease due to AOD may be originated in the largest industrial and urban areas in Chile, producing a negative impact on the hydrological resource, generated in the CAC.

Overview paper: New insights into aerosol and climate in the Arctic

Abstract. Motivated by the need to predict how the Arctic atmosphere will change in a warming world, this article summarizes recent advances made by the research consortium NETCARE (Network on Climate and Aerosols: Addressing Key Uncertainties in Remote Canadian Environments) that contribute to our fundamental understanding of Arctic aerosol particles as they relate to climate forcing. The overall goal of NETCARE research has been to use an interdisciplinary approach encompassing extensive field observations and a range of chemical transport, earth system, and biogeochemical models. Several major findings and advances have emerged from NETCARE since its formation in 2013. (1) Unexpectedly high summertime dimethyl sulfide (DMS) levels were identified in ocean water (up to 75 nM) and the overlying atmosphere (up to 1 ppbv) in the Canadian Arctic Archipelago (CAA). Furthermore, melt ponds, which are widely prevalent, were identified as an important DMS source (with DMS concentrations of up to 6 nM and a potential contribution to atmospheric DMS of 20 % in the study area). (2) Evidence of widespread particle nucleation and growth in the marine boundary layer was found in the CAA in the summertime, with these events observed on 41 % of days in a 2016 cruise. As well, at Alert, Nunavut, particles that are newly formed and grown under conditions of minimal anthropogenic influence during the months of July and August are estimated to contribute 20 % to 80 % of the 30–50 nm particle number density. DMS-oxidation-driven nucleation is facilitated by the presence of atmospheric ammonia arising from seabird-colony emissions, and potentially also from coastal regions, tundra, and biomass burning. Via accumulation of secondary organic aerosol (SOA), a significant fraction of the new particles grow to sizes that are active in cloud droplet formation. Although the gaseous precursors to Arctic marine SOA remain poorly defined, the measured levels of common continental SOA precursors (isoprene and monoterpenes) were low, whereas elevated mixing ratios of oxygenated volatile organic compounds (OVOCs) were inferred to arise via processes involving the sea surface microlayer. (3) The variability in the vertical distribution of black carbon (BC) under both springtime Arctic haze and more pristine summertime aerosol conditions was observed. Measured particle size distributions and mixing states were used to constrain, for the first time, calculations of aerosol–climate interactions under Arctic conditions. Aircraft- and ground-based measurements were used to better establish the BC source regions that supply the Arctic via long-range transport mechanisms, with evidence for a dominant springtime contribution from eastern and southern Asia to the middle troposphere, and a major contribution from northern Asia to the surface. (4) Measurements of ice nucleating particles (INPs) in the Arctic indicate that a major source of these particles is mineral dust, likely derived from local sources in the summer and long-range transport in the spring. In addition, INPs are abundant in the sea surface microlayer in the Arctic, and possibly play a role in ice nucleation in the atmosphere when mineral dust concentrations are low. (5) Amongst multiple aerosol components, BC was observed to have the smallest effective deposition velocities to high Arctic snow (0.03 cm s−1).

High Arctic aircraft measurements characterising black carbon vertical variability in spring and summer

Abstract. The vertical distribution of black carbon (BC) particles in the Arctic atmosphere is one of the key parameters controlling their radiative forcing and thus role in Arctic climate change. This work investigates the presence and properties of these light-absorbing aerosols over the High Canadian Arctic (>70∘ N). Airborne campaigns were performed as part of the NETCARE project (Network on Climate and Aerosols: Addressing Key Uncertainties in Remote Canadian Environments) and provided insights into the variability of the vertical distributions of BC particles in summer 2014 and spring 2015. The observation periods covered evolutions of cyclonic disturbances at the polar front, which favoured the transport of air pollution into the High Canadian Arctic, as otherwise this boundary between the air masses largely impedes entrainment of pollution from lower latitudes. A total of 48 vertical profiles of refractory BC (rBC) mass concentration and particle size, extending from 0.1 to 5.5 km altitude were obtained with a Single-Particle Soot Photometer (SP2). Generally, the rBC mass concentration decreased from spring to summer by a factor of 10. Such depletion was associated with a decrease in the mean rBC particle diameter, from approximately 200 to 130 nm at low altitude. Due to the very low number fraction, rBC particles did not substantially contribute to the total aerosol population in summer. The analysis of profiles with potential temperature as vertical coordinate revealed characteristic variability patterns within specific levels of the cold and stably stratified, dome-like, atmosphere over the polar region. The associated history of transport trajectories into each of these levels showed that the variability was induced by changing rates and efficiencies of rBC import. Generally, the source areas affecting the polar dome extended southward with increasing potential temperature (i.e. altitude) level in the dome. While the lower dome was mostly only influenced by low-level transport from sources within the cold central and marginal Arctic, for the mid-dome and upper dome during spring it was found that a cold air outbreak over eastern Europe caused intensified northward transport of air from a corridor over western Russia to central Asia. This sector was affected by emissions from gas flaring, industrial activity and wildfires. The development of transport caused rBC concentrations in the second lowest level to gradually increase from 32 to 49 ng m−3. In the third level this caused the initially low rBC concentration to increase from <15 to 150 ng m−3. A shift in rBC mass-mean diameter, from above 200 nm in the lower polar dome dominated by low-level transport to <190 nm at higher levels, may indicate that rBC was affected by wet removal mechanisms preferential to larger particle diameters when lifting processes were involved during transport. The summer polar dome had limited exchange with the mid-latitudes. Air pollution was supplied from sources within the marginal Arctic as well as by long-range transport, but in both cases rBC was largely depleted in absolute and relative concentrations. Near the surface, rBC concentrations were <2 ng m−3, while concentrations increased to <10 ng m−3 towards the upper boundary of the polar dome. The mass mean particle diameter of 132 nm was smaller than in spring; nonetheless the summer mean mass size distribution resembled the spring distribution from higher levels, with depletion of particles >300 nm. Our work provides vertical, spatial and seasonal information of rBC characteristics in the polar dome over the High Canadian Arctic, offering a more extensive dataset for evaluation of chemical transport models and for radiative forcing assessments than those obtained before by other Arctic aircraft campaigns.

Distribution of Black Carbon in Topsoils of the Northeastern Qinghai-Tibet Plateau Under Natural and Anthropogenic Influences.

Black carbon (BC), ubiquitous in soils, plays an important role in global carbon cycles, the radiative heat balance of the Earth, pollutant fate, emissions of greenhouse gas, soil fertility, soil microbial community, and ecosystem stability. However, information on BC in topsoils of the northeastern Qinghai-Tibet Plateau is limited. Therefore, this study performed field sampling and analyzed contents of total BC and soot BC in topsoils. The results indicated that the contents of total BC in all soil samples ranged from 0.504 to 74.381gkg-1 with an average value of 5.152gkg-1, whereas those of soot BC were in the range of 0.400-15.200gkg-1 with a mean value of 1.719gkg-1. Contents of BC were significantly correlated with those of total carbon and total organic carbon. Soil types affected the distribution of soil BC. The contents of total BC in the loam soils were larger than those in the clay soils, whereas soot BC was more easily enriched in the clay soils. Total BC was negatively correlated with Ca, and soot BC was negatively correlated with Ti. The contents of soil BC in functional areas, such as agricultural and pastoral areas, industrial areas, and mining areas, were significantly higher than those in other areas, illustrating that anthropogenic activities drastically affected the distribution of soil BC. This study exhibits the fundamental information on soil BC in the northeastern Qinghai-Tibet Plateau to provide important knowledge on global soil carbon sink.

Distribution of black carbon and black nitrogen in physical soil fractions from soils seven years after an intense forest fire and their role as C sink

After vegetation fires, incorporation of pyrogenic organic matter (PyOM) into soil organic matter (SOM) shifts its composition toward higher aromaticity and to an increase of N-heterocyclic constituents, formerly introduced as black nitrogen (BN). To investigate the medium-term impact of these shifts on the quality of SOM and its role as an important C sink, the A horizon from soils of the fire-prone Sierra de Aznalcóllar (Southern Spain) were sampled 4 weeks and 7 years after a severe fire. The solid-state 13C and 15N nuclear magnetic resonance (NMR) spectra of the samples obtained 4 weeks after the fire indicated quick incorporation of PyOM into SOM. Correspondingly, pyrrole-type N dominated the organic N fraction. Seven years after the fire, the aryl C contribution decreased from 46% to 23% of organic C, although it was still higher at the burnt sites than in the unburnt reference soil (16%). This fast loss of PyOM may be due to erosion, transport into deeper soils or microbial decomposition. The contribution of the latter is in line with former incubation experiments with burnt soils from the same area. Comparably, in the recovered soil, BN was almost completely substituted by amide N. Studying the partitioning of PyOM among the density and particle size fractions of the soils, indicated that after medium-term recuperation, most PyOM occurred in the free and occluded particulate OM fractions (fPOM and oPOM). The low protection against microbial degradation and the low density of these fractions may explain the high PyOM losses from the studied soils either by decomposition or by transport. We suggested that formation of PyOM-soil mineral associates represents an important step for reducing losses of fire-derived charcoal due to biochemical mineralization and thus to its sequestration in soils.

Climate Impact of a Regional Nuclear Weapons Exchange: An Improved Assessment Based On Detailed Source Calculations

AbstractWe present a multiscale study examining the impact of a regional exchange of nuclear weapons on global climate. Our models investigate multiple phases of the effects of nuclear weapons usage, including growth and rise of the nuclear fireball, ignition and spread of the induced firestorm, and comprehensive Earth system modeling of the oceans, land, ice, and atmosphere. This study follows from the scenario originally envisioned by Robock, Oman, Stenchikov, et al. (2007, https://doi.org/10.5194/acp-7-2003-2007), based on the analysis of Toon et al. (2007, https://doi.org/10.5194/acp-7-1973-2007), which assumes a regional exchange between India and Pakistan of fifty 15 kt weapons detonated by each side. We expand this scenario by modeling the processes that lead to production of black carbon, in order to refine the black carbon forcing estimates of these previous studies. When the Earth system model is initiated with 5 × 109 kg of black carbon in the upper troposphere (approximately from 9 to 13 km), the impact on climate variables such as global temperature and precipitation in our simulations is similar to that predicted by previously published work. However, while our thorough simulations of the firestorm produce about 3.7 × 109 kg of black carbon, we find that the vast majority of the black carbon never reaches an altitude above weather systems (approximately 12 km). Therefore, our Earth system model simulations conducted with model‐informed atmospheric distributions of black carbon produce significantly lower global climatic impacts than assessed in prior studies, as the carbon at lower altitudes is more quickly removed from the atmosphere. In addition, our model ensembles indicate that statistically significant effects on global surface temperatures are limited to the first 5 years and are much smaller in magnitude than those shown in earlier works. None of the simulations produced a nuclear winter effect. We find that the effects on global surface temperatures are not uniform and are concentrated primarily around the highest arctic latitudes, dramatically reducing the global impact on human health and agriculture compared with that reported by earlier studies. Our analysis demonstrates that the probability of significant global cooling from a limited exchange scenario as envisioned in previous studies is highly unlikely, a conclusion supported by examination of natural analogs, such as large forest fires and volcanic eruptions.