Atmospheric Residence Time Research Articles

Increasing aerosol direct effect despite declining global emissions in MPI-ESM1.2

Abstract. Anthropogenic aerosol particles partially mask global warming driven by greenhouse gases, both directly by reflecting sunlight back to space and indirectly by increasing cloud reflectivity. In recent decades, emissions of anthropogenic aerosols have declined globally and at the same time shifted from the North American and European regions, foremost to Southeast Asia. Using simulations with the Max Planck Institute Earth System Model version 1.2 (MPI-ESM1.2), we find that the direct effect of aerosols has continued to increase despite declining emissions. Concurrently, the indirect effect has diminished in approximate proportion to the emissions. In this model, which employs parameterized aerosol effects with constant regional direct effect efficiency, the enhanced efficiency of aerosol radiative forcing in emissions is associated with less cloud masking, longer atmospheric residence times, and differences in aerosol optical properties.

A new procedure to validate and optimize 210Po measurements in atmospheric aerosols

The exposure to air fine aerosols can cause health effects due to inhalations of alpha emitters such as 222Rn daughters. Lead-210 and 210Po are mainly associated to aerosols with median aerodynamic diameter lower than 1 μm. The 210Po is characterized by having a high radiotoxicity. The precise measurement of 210Po in surface air aerosols is usually quite complex due to the significant contribution of the 210Pb on their concentrations. Additionally, there is no possible means to manufacture a certified material to validate the measurements of 210Pb and 210Po concentrations in surface air aerosols. For these reasons, this study aims to develop a novel and comprehensive methodology to validate 210Po measurements in surface air aerosols by preparing in our laboratory “standard samples” with known activities of both 210Pb and 210Po. A detailed sensitivity analysis on the precision of 210Po concentration measurements has been carried out as a function of the involved variables such as sampling time, time elapsed between the sampling start and 210Po self-deposition and the 210Po/210Pb activity ratio in surface air aerosols. This study is necessary to find the optimum conditions for a precise measurement of 210Po in surface air aerosols. In addition, this methodology has been applied for the determination of 210Po concentrations in 30 samplings campaigns of atmospheric aerosols carried out at the El Carmen campus (Huelva province) from March 25th to July 15th, 2022. The results obtained for 210Pb and 210Po concentrations and atmospheric aerosol residence times (via 210Po/210Pb activity ratio) were consistent with other previous works.

Natural Aerosols, Gaseous Precursors and Their Impacts in Greece: A Review from the Remote Sensing Perspective

The Mediterranean, and particularly its Eastern basin, is a crossroad of air masses advected from Europe, Asia and Africa. Anthropogenic emissions from its megacities meet over the Eastern Mediterranean, with natural emissions from the Saharan and Middle East deserts, smoke from frequent forest fires, background marine and pollen particles emitted from ocean and vegetation, respectively. This mixture of natural aerosols and gaseous precursors (Short-Lived Climate Forcers—SLCFs in IPCC has short atmospheric residence times but strongly affects radiation and cloud formation, contributing the largest uncertainty to estimates and interpretations of the changing cloud and precipitation patterns across the basin. The SLCFs’ global forcing is comparable in magnitude to that of the long-lived greenhouse gases; however, the local forcing by SLCFs can far exceed those of the long-lived gases, according to the Intergovernmental Panel on Climate Change (IPCC). Monitoring the spatiotemporal distribution of SLCFs using remote sensing techniques is important for understanding their properties along with aging processes and impacts on radiation, clouds, weather and climate. This article reviews the current state of scientific know-how on the properties and trends of SLCFs in the Eastern Mediterranean along with their regional interactions and impacts, depicted by ground- and space-based remote sensing techniques.

Trans-boundary spatio-temporal analysis of Sentinel 5P tropospheric nitrogen dioxide and total carbon monoxide columns over Punjab and Haryana Regions with COVID-19 lockdown impact.

This study conducts a spatio-temporal analysis of tropospheric nitrogen dioxide (NO2) and total carbon monoxide (CO) concentrations in the Punjab and Haryana regions of India and Pakistan, using datasets from the Sentinel 5-Precursor (S5P) satellite. These regions, marked by diverse economic growth factors including population expansion, power generation, transportation, and agricultural practices, face similar challenges in atmospheric pollution, particularly evident in major urban centers like Delhi and Lahore, identified as pollution hotspots. The study also spotlights pollution associated with power plants. In urban areas, tropospheric NO2 levels are predominantly elevated due to vehicular emissions, whereas residential activities mainly contribute to CO pollution. However, precisely attributing urban CO sources is complex due to its longer atmospheric residence time and intricate circulation patterns. Notably, the burning of rice crop residue in November significantly exacerbates winter pollution episodes and smog, showing a more pronounced correlation with total CO than with tropospheric NO2 levels. The temporal analysis indicates that the months from October to December witness peak pollution, contrasted with the relatively cleaner period during the monsoon months of July to September. The severe pollution in the OND quarter is attributed to factors such as variations in boundary layer height and depletion of OH radicals. Furthermore, the study highlights the positive impact of the COVID-19 lockdown on air quality, with a significant decrease in NO2 concentrations during April, 2020 (Delhi: 59%, Lahore: 58%). However, the reduction in total CO columns was less significant. The study also correlates lockdown stringency with tropospheric NO2 columns (R2: 0.37 for Delhi, 0.25 for Lahore, 0.22 for Rawalpindi/Islamabad), acknowledging the influence of various meteorological and atmospheric variables. The research highlights the significant impact of crop residue burning on winter pollution levels, particularly on total CO concentrations. The study also shows the notable effect of the COVID-19 lockdown on air quality, significantly reducing NO2 levels. Additionally, it explores the correlation between lockdown stringency and tropospheric NO2 columns, considering various meteorological factors.

On the response of daily precipitation extremes to local mean temperature in the Yangtze River basin

This study explores the response of daily extreme precipitation (PEX) to local mean temperatures (T) of the previous 0-day (T0), 1-day (T1), and 1 to 9-days (T1–9) in the Yangtze River basin (YRB) using the non-stationarity test, binning method and copula theory. Results show that the annual scaling rate of PEX with T during 1961–2020 exhibits positive, negative and positive changing trends from southwest to northeast with the maximum magnitudes in the west, and experiences significant abrupt change only at 14.1% grids. The PEX-T scaling relation in the entire study period is predominantly characterized by a peak pattern over the YRB, with precipitation peaking at about 8 °C in the western highlands and at 25 °C in the east-central lowlands. However, the use of T1–9 yields a positive PEX-T pattern at more grids compared to T1 and T0, which highlights the important role of atmospheric moisture residence time in minimizing cooling artefacts in the scaling estimation. Generally, the full scaling rate of PEX with T in the study period is larger in the west-central part but smaller in the eastern YRB, and more sensitive to antecedent temperatures, with the ranges of −8–20%/°C, −8–30%/°C and −10–30%/°C against T0, T1 and T1–9, respectively. As precipitation intensifies, the full scaling decreases in plateau-mountain areas but increases in low-lying regions, gradually approaching the Clausius-Clapeyron (CC) scaling and exhibiting a “super-CC, CC-like and sub-CC scaling” pattern from west to east. Additionally, heavier precipitation events are most likely to occur at higher local temperatures in most areas even with peak structure. These findings provide new insights into the PEX-T relationships, which is conducive to understanding future changes in precipitation extremes and assessing precipitation-related risks under climate change.

Behavior of 222Rn, 220Rn and their progenies along a daily cycle for different meteorological situations: Implications on atmospheric aerosol residence times and Rn daughters' equilibrium factors

The correct assessment of the radiological hazard from radon and daughters, external and internal doses, residence times and equilibrium factors, implies the need to properly determine 222Rn (radon), 220Rn (thoron) and their respective short-lived progenies (214Pb and 214Bi, and 212Pb and 212Bi, respectively), where the precise measurements of both progenies are quite complex due to their very short half-lives. In addition, it is important to study the temporal behavior of all these radionuclides along daily cycles. Therefore, the aim of this study was to analyze the temporal evolution of radon, thoron and their progenies, and of their activity ratios along daily cycles for two different meteorological situations (synoptic and mesoscale processes). Radon and thoron were measured using a radon monitoring system, while their respective progenies were collected onto atmospheric filters using an ASS-500 sampler, and then measured by gamma-ray spectrometry. Furthermore, the different relationships between the concentrations of radionuclides and the different meteorological variables of interest (temperature, ABL height, and speed and direction of the wind) were found. Finally, the atmospheric aerosol residence times and Rn daughters’ equilibrium factors were estimated for each sampling carried out along the two daily cycles, finding results consistent with previous studies.

Assessing the role of atmospheric dispersion vs. emission strength in the southern Po Valley (Italy) using dispersion-normalised multi-time receptor modelling

In this paper, we applied the Dispersion Normalised Positive Matrix Factorisation (DN-PMF) approach recently proposed in the literature to provide a more realistic picture of the relative importance of emission strength vs. atmospheric dispersion conditions. The disentanglement of such effects is of great concern in pollution hot spots like the Po Valley (Italy), where particulate matter limit values are exceeded despite the existing abatement measures. To explore the potentiality of the DN-PMF approach – still scarcely applied in the literature – a well-chemically characterised PM1 (atmospheric particles with aerodynamic diameter <1 μm) dataset comprising samples collected at different time resolutions at an urban background site (Bologna) in the southern Po Valley was used. Indeed, it is well known that shallow mixing layers promote pollutant accumulation but this observation is not enough to exclude an enhancement of emission strength which could be tackled by appropriate abatement strategies.The source apportionment of sub-micron sized aerosols having a quite long atmospheric residence time in a complex environment like the Po Valley - which is also strongly impacted by secondary aerosol formation on a basin-scale - is generally quite challenging when using receptor models. Due to the availability of a huge dataset with variables having multiple time resolutions, in this work the DN-PMF was implemented in a multi-time resolution approach (MT) to achieve a better source identification and to gain knowledge about the relative importance of atmospheric dilution vs. emissions. A comparison between results obtained by the application of the regular multi time resolution (REG-MT) vs. the DN-MT approach is presented here for the five factors identified (nitrate-dominated, sulphate-dominated, biomass burning, mineral dust, and urban aerosol). The first interesting outcome is that REG-MT and DN-MT results do not point at significant differences in temporal patterns for aerosol components and sources impacting at the basin-scale (i.e. sulphate- and nitrate-dominated aerosol, biomass burning) thus suggesting that the diel modulation of these PM1 emissions is somehow masked by the stronger variability of the mixing layer. Conversely, contributions from local sources with more pronounced diel variation like traffic are quite well reproduced by DN-MT and the ambient concentrations are enhanced compared to REG-MT. This is an important piece of information highlighting that PM1 concentrations from local sources have been likely underestimated by REG-MT assessments.To our knowledge, this is one of the very few applications of DN-MT and the first one at a European site where the huge effort made to implement air pollution containment measures is still not very much effective in reducing PM levels; moreover, in this paper a detailed discussion about the possible interpretation of the output of DN-MT in terms of temporal patterns is reported.

Molecular Self-Organization in Surfactant Atmospheric Aerosol Proxies.

ConspectusAerosols are ubiquitous in the atmosphere. Outdoors, they take part in the climate system via cloud droplet formation, and they contribute to indoor and outdoor air pollution, impacting human health and man-made environmental change. In the indoor environment, aerosols are formed by common activities such as cooking and cleaning. People can spend up to ca. 90% of their time indoors, especially in the western world. Therefore, there is a need to understand how indoor aerosols are processed in addition to outdoor aerosols.Surfactants make significant contributions to aerosol emissions, with sources ranging from cooking to sea spray. These molecules alter the cloud droplet formation potential by changing the surface tension of aqueous droplets and thus increasing their ability to grow. They can also coat solid surfaces such as windows ("window grime") and dust particles. Such surface films are more important indoors due to the higher surface-to-volume ratio compared to the outdoor environment, increasing the likelihood of surface film-pollutant interactions.A common cooking and marine emission, oleic acid, is known to self-organize into a range of 3-D nanostructures. These nanostructures are highly viscous and as such can impact the kinetics of aerosol and film aging (i.e., water uptake and oxidation). There is still a discrepancy between the longer atmospheric lifetime of oleic acid compared with laboratory experiment-based predictions.We have created a body of experimental and modeling work focusing on the novel proposition of surfactant self-organization in the atmosphere. Self-organized proxies were studied as nanometer-to-micrometer films, levitated droplets, and bulk mixtures. This access to a wide range of geometries and scales has resulted in the following main conclusions: (i) an atmospherically abundant surfactant can self-organize into a range of viscous nanostructures in the presence of other compounds commonly encountered in atmospheric aerosols; (ii) surfactant self-organization significantly reduces the reactivity of the organic phase, increasing the chemical lifetime of these surfactant molecules and other particle constituents; (iii) while self-assembly was found over a wide range of conditions and compositions, the specific, observed nanostructure is highly sensitive to mixture composition; and (iv) a "crust" of product material forms on the surface of reacting particles and films, limiting the diffusion of reactive gases to the particle or film bulk and subsequent reactivity. These findings suggest that hazardous, reactive materials may be protected in aerosol matrixes underneath a highly viscous shell, thus extending the atmospheric residence times of otherwise short-lived species.

Assessment Vertical and Spatial Distribution of SO2 Concentration over Baghdad City (Case Study at 2022)

Abstract One of the most important issues at the present time in developed and developing countries alike is air pollution. Sulfur dioxides consider one of important gases pollutant that product from fossil fuel combustion such as oil and coal. It is considered one of the principal air pollutants that has contributed to premature deaths and respiratory illnesses. Globally SO2 also has a high spatial and temporal variability because of its short atmospheric residence time. In this study reanalysis data of SO2 concentration values is download from ERA5 website (fifth generation ECMWF reanalysis for global climate and weather) for months (Jan., April, July and Oct.) from year 2022, and for 8-height levels from ground surface to 5000 meter, for all area of Baghdad province, other atmospheric parameter also download such as boundary layer height BLH and wind and direction. Results show high values of SO2 in January relative to other months and the smallest values is in July at all 8-levels nearly. Spatial Speed and direction given opposite relation with SO2 concentration, while most high concentration of SO2 in located in Baghdad city center and area around because its represent the sources of pollutant.

Modeling atmospheric microplastic cycle by GEOS-Chem: An optimized estimation by a global dataset suggests likely 50 times lower ocean emissions

Modeling atmospheric microplastic cycle by GEOS-Chem: An optimized estimation by a global dataset suggests likely 50 times lower ocean emissions

Firework smoke: Impacts on urban air quality and deposition in the human respiratory system

Particle number concentrations and size distributions resulting from the firework displays held in Budapest, Hungary every year on St. Stephen's Day were studied over a period of seven years. In the year most impacted, the total particle number concentration reached its peak measured level of 369 × 103 cm−3 5 min after the end of the display, and returned to the pre-event state within 45 min. The fireworks increased hourly mean concentrations by a factor of 5–6, whereas the concentrations in the diameter range of 100–1000 nm, in which the magnitude of the increase was the greatest, were elevated by a factor of 20–25. An extra particle size mode at 203 nm was manifested in the size distributions as result of the fireworks. The PM10 mass concentrations at peak firework influence and as 1-h mean increased 123 and 58 times, respectively, relative to the concentration before the display. The smoke was characterised by a relatively short overall atmospheric residence time of 25 min. Spatiotemporal dispersion simulations revealed that there were substantial vertical and horizontal concentration gradients in the firework plume. The affected area made up a large part of the city. Not only the spectators of the display at the venue and nearby areas, but the population located further away downwind of the displays and more distant, large and populous urban quarters were affected by the plume and its fallout. The fireworks increased the deposition rate in the respiratory system of females by a factor of 4, as a conservative estimate. The largest surface density deposition rates were seen in the segmental and sub-segmental bronchi, which represents an excessive risk to health. Compared to adults, children were more susceptible to exposure, with the maximum surface density deposition rates in their case being three times those of adults in the trachea.

Unexpected self-lofting and dynamical confinement of volcanic plumes: the Raikoke 2019 case

Recent research has provided evidence of the self-lofting capacity of smoke aerosols in the stratosphere and their self-confinement by persistent anticyclones, which prolongs their atmospheric residence time and radiative effects. By contrast, the volcanic aerosols—composed mostly of non-absorptive sulphuric acid droplets—were never reported to be subject of dynamical confinement. Here we use high-resolution satellite observations to show that the eruption of Raikoke volcano in June 2019 produced a long-lived stratospheric anticyclone containing 24% of the total erupted mass of sulphur dioxide. The anticyclone persisted for more than 3 months, circumnavigated the globe three times, and ascended diabatically to 27 km altitude through radiative heating of volcanic ash contained by the plume. The mechanism of dynamical confinement has important implications for the planetary-scale transport of volcanic emissions, their stratospheric residence time, and atmospheric radiation balance. It also provides a challenge or “out of sample test” for weather and climate models that should be capable of reproducing similar structures.

The lifetime of charged dust in the atmosphere.

Wind-blown dust plays a critical role in numerous geophysical and biological systems, yet current models fail to explain the transport of coarse-mode particles (>5 μm) to great distances from their sources. For particles larger than a few microns, electrostatic effects have been invoked to account for longer-than-predicted atmospheric residence times. Although much effort has focused on elucidating the charging processes, comparatively little effort has been expended understanding the stability of charge on particles once electrified. Overall, electrostatic-driven transport requires that charge remain present on particles for days to weeks. Here, we present a set of experiments designed to explore the longevity of electrostatic charge on levitated airborne particles after a single charging event. Using an acoustic levitator, we measured the charge on particles of different material compositions suspended in atmospheric conditions for long periods of time. In dry environments, the total charge on particles decayed in over 1 week. The decay timescale decreased to days in humid environments. These results were independent of particle material and charge polarity. However, exposure to UV radiation could both increase and decrease the decay time depending on polarity. Our work suggests that the rate of charge decay on airborne particles is solely determined by ion capture from the air. Furthermore, using a one-dimensional sedimentation model, we predict that atmospheric dust of order 10 μm will experience the largest change in residence time due to electrostatic forces.

Structure and Protein-Protein Interactions of Ice Nucleation Proteins Drive Their Activity

Microbially-produced ice nucleating proteins (INpro) are unique molecular structures with the highest known catalytic efficiency for ice formation. Airborne microorganisms utilize these proteins to enhance their survival by reducing their atmospheric residence times. INpro also have critical environmental effects including impacts on the atmospheric water cycle, through their role in cloud and precipitation formation, as well as frost damage on crops. INpro are ubiquitously present in the atmosphere where they are emitted from diverse terrestrial and marine environments. Even though bacterial genes encoding INpro have been discovered and sequenced decades ago, the details of how the INpro molecular structure and oligomerization foster their unique ice-nucleation activity remain elusive. Using machine-learning based software AlphaFold 2 and trRosetta, we obtained and analysed the first ab initio structural models of full length and truncated versions of bacterial INpro. The modeling revealed a novel beta-helix structure of the INpro central repeat domain responsible for ice nucleation activity. This domain consists of repeated stacks of two beta strands connected by two sharp turns. One beta-strand is decorated with a TxT amino acid sequence motif and the other strand has an SxL[T/I] motif. The core formed between the stacked beta helix-pairs is unusually polar and very distinct from previous INpro models. Using synchrotron radiation circular dichroism, we validated the β-strand content of the central repeat domain in the model. Combining the structural model with functional studies of purified recombinant INpro, electron microscopy and modeling, we further demonstrate that the formation of dimers and higher-order oligomers is key to INpro activity. Using computational docking of the new INpro model based on rigid-body algorithms we could reproduce a previously proposed homodimer structure of the INpro CRD with an interface along a highly conserved tyrosine ladder and show that the dimer model agrees with our functional data. The parallel dimer structure creates a surface where the TxT motif of one monomer aligns with the SxL[T/I] motif of the other monomer widening the surface that interacts with water molecules and therefore enhancing the ice nucleation activity. This work presents a major advance in understanding the molecular foundation for bacterial ice-nucleation activity.

The impact of different atmospheric phenomena to cosmogenic 22Na/7Be ratio

The isotopic ratio of two cosmogenic isotopes, 22Na and 7Be, has been recognized as a possible tracer for atmospheric dynamics. We studied how different atmospheric phenomena affect the 22Na/7Be ratio that are known to affect the ground level 7Be concentrations. The 22Na/7Be ratio was studied in the following context: estimation of aerosol residence time, in the intrusions of stratospheric air after Sudden Stratospheric Warming (SSW) events, seasonal variations due to different atmospheric mixing conditions and finally the interannual variations caused by the large-scale atmospheric circulation such as North Atlantic Oscillation (NAO), Arctic Oscillation (AO), Scandinavian Pattern (SCAND) and Quasi-Biennial Oscillation (QBO). This study utilized airborne radioactivity monitoring data from three Finnish stations located in Rovaniemi (66.51 °N, 25.73 °E), Kajaani (64.08 °N, 27.71 °E) and Kotka (60.48 °N, 26.92 °E). The theoretical calculations were performed to see how the 22Na/7Be ratio changes as a function of altitude during when produced by the galactic cosmic rays. The calculations showed that the 22Na/7Be ratio is higher in the stratosphere and lower in the troposphere. At mid-stratosphere level the ratio was 0.001, at tropopause level approximately 0.0007 and at ground level approximately 0.00045. Due to the different half-lives of 22Na and 7Be the mean atmospheric residence time can be estimefrom the radioactive decay law by assuming an initial activity concentration ratio of 0.0007 and using the measured ground level 22Na/7Be ratios. This resulted in the median atmospheric residence time as 91–95 days. The atmospheric impact on 22Na/7Be ratio was studied at different time scales starting from short-term impact from SSW, the known seasonal cycle and variations at interannual timescale. SSW events caused rapid increases in the ground level 7Be and 22Na concentrations while the impact on 22Na/7Be ratio was relatively small. A clear seasonal cycle in the 22Na/7Be ratio was observed where the 22Na/7Be ratio was at low value during November–February, increased during March–May, stayed at stable high value during June–July and steadily decreased during August–October. The long-term average for 22Na/7Be ratio was established to be 1.1 × 10−4 by using the Kotka data from 1993 to 2020. During 1995–2009, the 22Na/7Be ratio was below the long-term average, and during 2010–2020, generally above. The interannual variations in the 22Na/7Be ratio were studied by using wavelet transform analysis of the Kotka data. The analysis showed 4-6-year and 11-year periodicities. The wavelet coherence analyses with AO, NAO, SCAND, QBO and Southern Oscillation (SO) indices showed that the shorter periodicity was caused by the NAO/AO effects the atmospheric circulation in Scandinavia and hence the transport of the isotopes from upper atmosphere to ground level. The observed coherence with the Southern Oscillation Index (SOI) starting from 2012 onwards appeared at an approximately 3–4year scale while the AO and NAO had a coherence at an approximately 6-year scale. The observed 11-year periodicity was caused by the Solar cycle which modulates the 7Be and 22Na production in the upper atmosphere.

The importance of continental evaporation for precipitation in Colombia: A baseline combining observations from stable isotopes and modelling moisture trajectories

AbstractThe hydroclimatology of Northern South America responds to the coupling between the Pacific and Atlantic oceans, the Amazon–Andes interactions, and the orographic barrier of the regional Andes. The relative contributions of oceanic and terrestrial moisture sources have been mostly evaluated in modelling studies, with limited observational data for validation. We combine observations from stable isotopes in precipitation and output from the Lagrangian moisture trajectory tracking model FLEXPART to characterize and contrast the relative contribution of oceanic (from the Atlantic and the Pacific) and terrestrial (from different regions in the continent) moisture sources to mean monthly precipitation in the Andes and Caribbean regions of Colombia. Our results indicate that most moisture becoming rain in the region has an atmospheric residence time that deviates from commonly assumed 10 days. These residence times vary between source and sink regions from 1 day in the case of recycling to more than 10 days in Andean precipitation originating in the Atlantic Ocean. Common integration times for both regions from all sources are commonly in the order of three to 7 days. Most precipitation in the region comes from terrestrial sources including moisture recycling from the same region (&gt;30% for all months), the Orinoco River basin (up to 28% in April), and the northern Amazon basin (up to 17% in June, July, and August); followed by individually considered oceanic sources including the Tropical South Pacific (up to 30% monthly in October, November and December) and Tropical North Atlantic (up to 30% monthly for January). The fact that a significant proportion of rainfall is recycled highlights that water availability in the Andean and Caribbean regions of Colombia could potentially be altered by current widespread and pervasive changes in vegetation cover. More generally, our results highlight the need to assess the hydrological consequences of land cover change in South America, particularly in a country like Colombia where water, food, and energy security all depend directly on precipitation.

Spatial and Temporal Trends in Mineral Dust Provenance in the South Pacific—Evidence From Mixing Models

AbstractMineral dust is an important component of the Earth system due to its role in oceanic nutrient supply, cloud formation and its radiative properties. Changes in transport pathways and fluxes of mineral dust have attracted increased attention using radiogenic isotope analysis for detailed investigation of changing dust sources through time. However, multi‐isotope studies provide complex datasets of dust provenance, often without exact quantification of source contributions. Here we use Bayesian mixing models and existing radiogenic isotope data to quantify changes in South Pacific dust provenance for the Holocene and the Last Glacial Maximum (LGM; ∼18–24 ka BP). Testing different model configurations showed grouping small source regions to single continental scale end members prior to modeling can lead to biased results, and so we group model outputs post‐modeling. During the LGM, a higher proportion (mean 53%) of dust entering the South Pacific was South American in origin, compared to a Holocene mean of 31%. In contrast, Australian dust contributions were lower during the LGM (mean 38%) than Holocene (mean 55%), with significant spatial gradients for both time slices. In the subpolar South Pacific, the high representation of South American dust during the LGM (up to ∼75%) coincides with larger dust particles; together indicating that far‐traveled dust transport was facilitated by long atmospheric residence times and an accelerated westerly wind circulation during this time. Our study shows how Bayesian mixing models provide valuable constraints for dust source contributions, an approach which may help in the calibration of atmospheric models, using complex isotopic datasets.

A Study on the N2O Reduction Rate According to Temperature and Residence Time in the Exhaust Gas Atmosphere Emitted on Combustion of Air and Oxygen.

N2O is a hazardous greenhouse gas. It should be reduced to solve global warming problems. In this study, experiments of N2O thermal decomposition were conducted by simulating the exhaust gas atmosphere emitted during the combustion of air and pure oxygen in an actual circulating fluidized bed system and incinerator system. As a result of comparing the N2O reduction rate in N2 and CO2 atmospheres, the N2O reduction rate in the CO2 atmosphere was 20% higher than that in the N2 atmosphere. It is judged that the N2O reduction rate is high in a CO2 atmosphere (exhaust gas from pure oxygen combustion) due to complex factors such as the reverse reaction, the diffusion coefficient, and static pressure-specific heat. Therefore, pure oxygen combustion increases the reduction rate of nitrous oxide. In addition, when operated with an appropriate residence time and temperature, a reduction effect of more than 95% can be expected, and the fuel consumption rate is also expected to improve.

Emerging Major Role of Organic Aerosols in Explaining the Occurrence, Frequency, and Magnitude of Haze and Fog Episodes during Wintertime in the Indo Gangetic Plain.

Aerosols are an important part of Earth’s atmosphere. They can absorb, scatter, or reflect the incoming solar radiation, which results in heating or cooling of Earth, thus impacting its climate. It affects the health of exposed human population adversely, reduces visibility, disturbs environmental systems, and causes material damage. This study summarizes the research carried out to understand the role of aerosol load and its physicochemical characteristics on occurrence, frequency, and magnitude of haze and fog events during wintertime within the Indo Gangetic Plain (IGP) in the past decade. For most species, the highest concentration was measured during foggy events at night-time over the winter season. A few species such as water-soluble organic and inorganic carbon (WSOC and WSIC), K+, SO42–, and NO3–, owing to their hygroscopic nature, were efficiently scavenged, resulting in their lower concentration within the interstitial aerosol during fog episodes. Oligomerization with hydroxy and carbonyl functional groups during AFP (activating fog period) and DFP (dissipating fog period), respectively, accompanied by acidic aerosol (having catalytic ability) and high aerosol liquid water content conditions was found to be significant. Whereas the fragmentation process was dominant along with functionalization of −RCOOH or carbonyl (aldehyde/ketone) and −RCOOH moieties during FP (fog period) and PoFP (post-fog period), respectively. Transition metals play an important role in aqueous production of secondary organic aerosol (SOA) especially during the night-time. Crustal sources had the highest scavenging efficiency along with WSOC playing an important role in nucleation scavenging. Fine droplets had a higher concentration of species with a larger fraction of highly oxidized organic matter (OM) as compared to coarse or medium size droplets. Also, a new approach to calculate absorption by black carbon (BC) and brown carbon (BrC) was proposed, which found the water-soluble brown carbon (WSBrC) absorption value in aerosol to be up to 1.8 times higher than that measured in their corresponding aqueous extracts. Organic aerosol plays a vital role in facilitating fog formation and is responsible for the longer residence time in the ambient atmosphere. Ammonia plays an important role in stabilizing organic aerosol and aids to this recurring haze–fog–haze cycle that is dominant during wintertime in the IGP. Therefore, controlling the major anthropogenic sources of organic aerosol and ammonia should be our top priority in this part of the world.

Size-Resolved Community Structure of Bacteria and Fungi Transported by Dust in the Middle East.

The atmosphere plays an important role in transporting microorganisms on a global scale, yet the processes affecting the composition of the airborne microbiome, the aerobiome, are not fully outlined. Here we present the community compositions of bacteria and fungi obtained by DNA amplicon-sequencing of aerosol samples collected in a size-resolved manner during nine consecutive days in central Israel. The campaign captured dust events originating from the Sahara and the Arabian deserts, as well as days without dust (“clear days”). We found that the source of the aerosol was the main variable contributing to the composition of both fungal and bacterial communities. Significant differences were also observed between communities representing particles of different sizes. We show evidence for the significant transport of bacteria as cell-aggregates and/or via bacterial attachment to particles during dust events. Our findings further point to the mixing of local and transported bacterial communities, observed mostly in particles smaller than 0.6 μm in diameter, representing bacterial single cells. Fungal communities showed the highest dependence on the source of the aerosols, along with significant daily variability, and without significant mixing between sources, possibly due to their larger aerodynamic size and shorter atmospheric residence times. These results, obtained under highly varied atmospheric conditions, provide significant assurances to previously raised hypotheses and could set the course for future studies on aerobiome composition.