Sulfate alters aerosol absorption properties in East Asian outflow

Black carbon (BC) and brown carbon (BrC) aerosols that are released from the combustion of fossil fuels and biomass are of great concern because of their light-absorbing ability and great abundance associated with various anthropogenic sources, particularly in East Asia. However, the optical properties of ambient aerosols are dependent on the mixing state and the chemical composition of absorbing and non-absorbing aerosols. Here we examined how, in East Asian outflows, the parameters of the aerosol optical properties can be altered seasonally in conjunction with the mixing state and the chemical composition of aerosols, using 3-year aerosol measurements. Our findings highlight the important role played by sulfate in East Asia during the warm season in both enhancing single scattering albedo (SSA) and altering the absorption properties of aerosols-enhancing mass absorption cross section of BC (MAC(BC)) and reducing MAC of BrC (MAC(BrC),(370)). Therefore we suggest that in global radiative forcing models, particular attention should be paid to the consideration of the accurate treatment of the SO2 emission changes in the coming years in this region that will result from China's air quality policy.Peer reviewe

Source signatures from combined isotopic analyses of PM2.5 carbonaceous and nitrogen aerosols at the peri-urban Taehwa Research Forest, South Korea in summer and fall.

Isotopes are essential tools to apportion major sources of aerosols. We measured the radiocarbon, stable carbon, and stable nitrogen isotopic composition of PM2.5 at Taehwa Research Forest (TRF) near Seoul Metropolitan Area (SMA) during August-October 2014. PM2.5, TC, and TN concentrations were 19.4 ± 10.1 μg m-3, 2.6 ± 0.8 μg C m-3, and 1.4 ± 1.4 μg N m-3, respectively. The δ13C of TC and the δ15N of TN were - 25.4 ± 0.7‰ and 14.6 ± 3.8‰, respectively. EC was dominated by fossil-fuel sources with Fff (EC) of 78 ± 7%. In contrast, contemporary sources were dominant for TC with Fc (TC) of 76 ± 7%, revealing the significant contribution of contemporary sources to OC during the growing season. The isotopic signature carries more detailed information on sources depending on air mass trajectories. The urban influence was dominant under stagnant condition, which was in reasonable agreement with the estimated δ15N of NH4+. The low δ15N (7.0 ± 0.2‰) with high TN concentration was apparent in air masses from Shandong province, indicating fossil fuel combustion as major emission source. In contrast, the high δ15N (16.1 ± 3.2‰) with enhanced TC/TN ratio reveals the impact of biomass burning in the air transported from the far eastern border region of China and Russia. Our findings highlight that the multi-isotopic composition is a useful tool to identify emission sources and to trace regional sources of carbonaceous and nitrogen aerosols

Regional characteristics of fine aerosol mass increase elucidated from long-term observations and KORUS-AQ campaign at a Northeast Asian background site

Funding Information: This research was supported by the National Research Foundation of Korea (NRF), funded by the Ministry of Science and ICT (MSIT) (NRF2020M3G1A111499813). S. Lim was supported by the National Research Foundation of Korea (NRF) from the Ministry of Science and ICT (2018R1D1A1B07050849 and 2021R1C1C2011543). M. Lee thanks to the support by the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT (NRF2020R1A2C301459213). S.-W. Kim was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF), funded by the Ministry of Education (2017R1D1A1B06032548). Funding to K.-S. Kang was provided by the National Institute of Environmental Research (NIER-RP2017-166). Funding Information: This research was supported by the National Research Foundation of Korea (NRF), funded by the Ministry of Science and ICT (MSIT) (NRF2020M3G1A111499813). S. Lim was supported by the National Research Foundation of Korea (NRF) from the Ministry of Science and ICT (2018R1D1A1B07050849 and 2021R1C1C2011543). M. Lee thanks to the support by the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT (NRF2020R1A2C301459213). S.-W. Kim was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF), funded by the Ministry of Education (2017R1D1A1B06032548). Funding to K.-S. Kang was provided by the National Institute of Environmental Research (NIER-RP2017-166). Publisher Copyright: © 2022 The Author(s)Northeast Asia has suffered from severe PM2.5 pollution and the exact mechanisms have yet to be fully understood. Here, we investigated the transformation processes of submicron aerosols using a 4-year data set obtained at Jeju, a Northeast Asian background site. The diurnal-cycle constrained empirical orthogonal function analysis of nanoparticle size-number distribution distinguished 2 modes: burst of nucleation-Aitken particles and increase in accumulation mode particles, representing “new particle formation and growth” and “PM2.5 mass increase,” respectively. In these events, aerosol and meteorological characteristics changed progressively over several days, revealing that the PM2.5 mass increase is an episodic event occurring on a regional scale. The increase in PM2.5 mass was accompanied by an increase in aerosol liquid water content, which correlated well with SO4-2 and NO3, and a decrease in incoming solar radiation (-14.1 Wm-2 day-1) constituting a positive feedback. The “transport/haze” episode of KOREA-U.S. Air Quality campaign corresponds to “PM2.5 mass increase,” during which the vertical evolution of particles demonstrates that nanoparticles ≥3.5 nm were entrained into the shallow boundary layer upon vertical mixing and converted to accumulation-mode particles ≥0.3 mm at relative humidity (RH) exceeding the deliquescence RH of secondary inorganic aerosol (SIA). Coincidently, at ground, the coating thickness of refractory black carbon (rBC) (48 ± 39 nm) and SIA concentration increased. Furthermore, the diameter of rBC (180-220 nm)-containing particle in core-shell configuration linearly increased with PM2.5 mass, reaching 300-400 nm at PM2.5 ≥ 40 mg m-3.This observational evidence suggests that the thick coating of rBCs resulted from the active conversion of condensable gases into the particulate phase on the rBC surface, thereby increasing the mass of the accumulation-mode aerosol. Consequently, this result complies with the strategy to reduce primary emissions of gaseous precursors for SIA and particulates such as rBC as a way to effectively mitigate haze pollution as well as climate change in Northeast Asia.Peer reviewe

La variabilité et de l'évolution de carbone-suie en Europe au cours des 140 dernières années, extraites d'une carotte de glace du Caucase

Le carbone-suie, ou "black carbon" (BC), est considéré comme le deuxième plus grand contributeur d'origine anthropique au changement climatique, après le dioxyde de carbone, en raison de son importante capacité à absorber la lumière (Bond et al., 2013). Malgré son influence sur le système climatique, les observations pluriannuelles des teneurs atmosphériques de BC demeurent rares, particulièrement en Europe. Cette étude propose une reconstruction nouvelle de la variabilité passée du BC atmosphérique à partir de l'analyse d'une carotte de glace forée au glacier de l'Elbrus (ELB), situé dans le Caucase en Russie. Un analyseur de carbone-suie SP2 (Single Particle Soot Photometer) a été exploité pour l'analyse du BC réfractaire (rBC) sur 153m de carotte de glace couvrant les derniers 140 ans. Un nouveau système analytique couplant un nébuliseur APEX-Q et le SP2, intégré au sein d'un système d'Analyse en Flux Continu, a été développée et a permis d'obtenir un enregistrement unique quasi-continu du rBC. La glace de l'Elbrus révèle une augmentation marquée des teneurs en rBC entre les années 1870 et 1980, suivie d'une diminution des concentrations jusqu'en 2000 environ. Au cours de la dernière décennie, les concentrations en rBC demeurent stables. Parallèlement, une augmentation des niveaux de fond jusqu'en 1980 indique clairement un impact non négligeable des émissions anthropiques sur la charge en BC atmosphérique à des échelles spatiales très larges, et notamment dans la troposphère libre. Une étude fine des inventaires d'émissions de BC disponibles et la modélisation FLEXPART viennent confirmer que l'augmentation forte de rBC depuis 1920 est principalement due aux émissions anthropiques de BC. Une analyse du gradient est-ouest des dépôts de rBC à haute altitude au cours de la dernière décennie a été réalisée, en comparant l'archive récente (10 ans) de l'Elbrus avec deux autres enregistrements provenant du Col du Dôme (CDD, France) et du Colle Gnifetti (CG, Italie). Les concentrations à l'Elbrus se révèlent deux à trois fois supérieures à celles des autres sites, une différence liée à l'intensité plus forte des sources en Europe de l'Est et confirmée par la modélisation FLEXPART. Les combustions de biomasse se trouvent identifiées comme la principale cause de variabilité interannuelle à l'Elbrus en été. Sur les derniers 10 ans, une diminution statistiquement significative des concentrations en rBC dans la neige est détectée au CDD, un résultat qui s'oppose aux observations réalisées à l'Elbrus où une tendance à l'augmentation au cours des périodes estivales est identifiée. Ces tendances, aussi bien CDD et ELB, sont relativement cohérentes avec les inventaires d'émissions de BC anthropiques disponibles. Ces enregistrements nouveaux et continus de rBC dans plusieurs carottes de glace européennes viennent faire progresser notre compréhension des évolutions passées des sources et de la charge atmosphérique du BC en Europe. Ces enregistrements peuvent participer à une meilleure évaluation de l'efficacité des politiques passées et actuelles de réduction des émissions de BC, ainsi qu'à une amélioration des inventaires d'émission.Black carbon (BC) is considered as the second largest man-made contributor to global warming after carbon dioxide due to its highly light-absorbing ability (Bond et al., 2013). Despite its climatic role, multi-year observations of ambient BC concentrations are scarce, in particular over Europe. In this thesis, we reconstructed past variability of atmospheric BC using an ice core from the Elbrus glacier (ELB), Caucasus in Russia. We have used a single particle soot photometer (SP2) to retrieve refractive BC (rBC) along 153 m of ice core covering the last 140 years. We have developed and validated a novel analytical system coupling of APEX-Q nebulization to SP2 in a Continuous-flow Analysis system to derive a unique quasi-continuous record of rBC. Results reveal a substantial rBC increase since 1870s lasting until 1980, followed by a decrease until ~2000. In the last decade, rBC concentrations remained constant. In parallel, an increase in background concentration until 1980 clearly highlights that anthropogenic BC emissions have substantially affected the atmospheric BC loading on a very large spatial scale, particularly in the free troposphere. A comparison with the estimated BC reaching the ELB site using a BC emission inventory/FLEXPART modeling confirms that the strong rBC increase since around 1920 is mainly due to anthropogenic BC emissions. Analysis of the East-West gradient of rBC deposited in snow over the last decade is investigated comparing the recent archive (10-year) at ELB with two other records from Col du Dôme (CDD), France, and Colle Gnifetti (CG), Italy. Concentrations at ELB are 2-3 times higher than at other sites, which is linked to source intensity in the Eastern part of Europe, as confirmed by the FLEXPART modelling. Biomass burning is identified as a main cause of inter-annual variability at ELB during summer time. Over the last decade, a statistically significant reduction of rBC concentration in snow is found at CDD, opposite to what is found at ELB with an increasing trend observed for summer periods. These trends are also fairly consistent with anthropogenic BC emissions inventories. Availability of continuous records of rBC in European ice cores improved our understanding of past evolution of atmospheric BC over Europe. They can be used to assess efficiency of past and current emission reduction policies and improve emission inventories

Oxidation pathways and emission sources of atmospheric particulate nitrate in Seoul: based on δ<SUP>15</SUP>N and Δ<SUP>17</SUP>O measurements

International audiencePM2.5 haze pollution driven by secondary inorganic NO3- has been a great concern in East Asia. It is, therefore, imperative to identify its sources and oxidation processes, for which nitrogen and oxygen stable isotopes are powerful tracers. Here, we determined the δ15N (NO3-) and Δ17O (NO3-) of PM2.5 in Seoul during the summer of 2018 and the winter of 2018-2019 and estimated quantitatively the relative contribution of oxidation pathways for particulate NO3- and investigated major NOx emission sources. In the range of PM2.5 mass concentration from 7.5 µg m−3 (summer) to 139.0 µg m−3 (winter), the mean δ15N was −0.7 ‰ ± 3.3 ‰ and 3.8 ‰ ± 3.7 ‰, and the mean Δ17O was 23.2 ‰ ± 2.2 ‰ and 27.7 ‰ ± 2.2 ‰ in the summer and winter, respectively. While OH oxidation was the dominant pathway for NO3- during the summer (87 %), nighttime formation via N2O5 and NO3 was relatively more important (38 %) during the winter, when aerosol liquid water content (ALWC) and nitrogen oxidation ratio (NOR) were higher. Interestingly, the highest Δ17O was coupled with the lowest δ15N and highest NOR during the record-breaking winter PM2.5 episodes, revealing the critical role of photochemical oxidation process in severe winter haze development. For NOx sources, atmospheric δ15N (NOx) estimated from measured δ15N (NO3-) considering isotope fractionation effects indicates vehicle emissions as the most important emission source of NOx in Seoul. The contribution from biogenic soil and coal combustion was slightly increased in summer and winter, respectively. Our results built on a multiple-isotope approach provide the first explicit evidence for NO3- formation processes and major NOx emission sources in the Seoul megacity and suggest an effective mitigation measure to improve PM2.5 pollution

Dust Criteria Derived from Long-Term Filter and Online Observations at Gosan in South Korea

Dust and pollution are frequently mixed together in East Asia, causing large uncertainties in assessing climate change and environmental influence and in relevant policymaking. To discern the dust effect on particle mass, we carried out long-term measurements of the mass and key chemical compositions of PM10, PM2.5, and PM1 from August 2007 to February 2012 and collected hourly data of PM10 and PM2.5 concentrations from January 2012 to October 2020 at Gosan, South Korea. The principal component analysis of measured species reveals two dominant factors, pollution and dust, accounting for 46% and 16% of the total variance, respectively. The mode distribution of PM10, PM2.5, and PM1 mass in addition to the dust events helps to provide a robust criterion of the dust impact. Dust can be identified by the mean + standard deviation (σ) of PM10, while the threshold is down to the mean concentration when dust particles experience precipitation. High PM2.5 concentration also presents dust impact; however, the criterion decreases from mean + σ in 2007–2012 to mean in 2012–2020. It indicates that dust is no longer a high-concentration event of PM2.5, but its influence gradually appears in low-concentration particles. Therefore, the dust criterion obtained from long-term PM10 concentration data is robust; however, the standard is based on PM2.5 changes over time and still needs to be determined by follow-up long-term observations

Robust Evidence of 14C, 13C, and 15N Analyses Indicating Fossil Fuel Sources for Total Carbon and Ammonium in Fine Aerosols in Seoul Megacity.

Carbon- and nitrogen-containing aerosols are ubiquitous in urban atmospheres and play important roles in air quality and climate change. We determined the 14C fraction modern (fM) and δ13C of total carbon (TC) and δ15N of NH4+ in the PM2.5 collected in Seoul megacity during April 2018 to December 2019. The seasonal mean δ13C values were similar to -25.1‰ ± 2.0‰ in warm and -24.2‰ ± 0.82‰ in cold seasons. Mean δ15N values were higher in warm (16.4‰ ± 2.8‰) than in cold seasons (4.0‰ ± 6.1‰), highlighting the temperature effects on atmospheric NH3 levels and phase-equilibrium isotopic exchange during the conversion of NH3 to NH4+. While 37% ± 10% of TC was apportioned to fossil-fuel sources on the basis of fM values, δ15N indicated a higher contribution of emissions from vehicle exhausts and electricity generating units (power-plant NH3 slip) to NH3: 60% ± 26% in warm season and 66% ± 22% in cold season, based on a Bayesian isotope-mixing model. The collective evidence of multiple isotope analysis reasonably supports the major contribution of fossil-fuel-combustion sources to NH4+, in conjunction with TC, and an increased contribution from vehicle emissions during the severe PM2.5 pollution episodes. These findings demonstrate the efficacy of a multiple-isotope approach in providing better insight into the major sources of PM2.5 in the urban atmosphere

Black carbon variability since preindustrial times in the eastern part of Europe reconstructed from Mt. Elbrus, Caucasus, ice cores

International audienceBlack carbon (BC), emitted by fossil fuel combustion and biomass burning, is the second largest man-made contributor to global warming after carbon dioxide (Bond et al., 2013). However, limited information exists on its past emissions and atmospheric variability. In this study, we present the first high-resolution record of refractory BC (rBC, including mass concentration and size) reconstructed from ice cores drilled at a high-altitude eastern European site in Mt. Elbrus (ELB), Caucasus (5115 m a.s.l.). The ELB ice core record, covering the period 1825–2013, reflects the atmospheric load of rBC particles at the ELB site transported from the European continent with a larger rBC input from sources located in the eastern part of Europe. In the first half of the 20th century, European anthropogenic emissions resulted in a 1.5-fold increase in the ice core rBC mass concentrations with respect to its level in the preindustrial era (before 1850). The summer (winter) rBC mass concentrations increased 5-fold (3.3-fold) in 1960–1980, followed by a decrease until  ∼  2000. Over the last decade, the rBC signal for summertime slightly increased. We have compared the signal with the atmospheric BC load simulated using past BC emissions (ACCMIP and MACCity inventories) and taken into account the contribution of different geographical regions to rBC distribution and deposition at the ELB site. Interestingly, the observed rBC variability in the ELB ice core record since the 1960s is not in perfect agreement with the simulated atmospheric BC load. Similar features between the ice core rBC record and the best scenarios for the atmospheric BC load support anthropogenic BC increase in the 20th century being reflected in the ELB ice core record. However, the peak in BC mass concentration observed in  ∼  1970 in the ice core is estimated to occur a decade later from past inventories. BC emission inventories for the period 1960s–1970s may be underestimating European anthropogenic emissions. Furthermore, for summertime snow layers of the 2000s, the slightly increasing trend of rBC deposition likely reflects recent changes in anthropogenic and biomass burning BC emissions in the eastern part of Europe. Our study highlights that the past changes in BC emissions of eastern Europe need to be considered in assessing ongoing air quality regulation