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• Comparison of portable black carbon monitors with standard aethalometer AE33. • The effect of ambient environment and built-in algorithms were investigated. • Suggestion on application scenario of each micro monitor proposed. Black carbon (BC) is associated with adverse human health and climate change. Mapping BC spatial distribution imperatively requires low-cost and portable devices. Several portable BC monitors are commercially available, but their accuracy and reliability are not always satisfactory during continuous field observation. This study evaluated three models of portable black carbon monitors, C12, MA350 and DST, and investigates the factors that affect their performance. The monitors were tested in urban Beijing, where portable devices running for one month alongside a regular-size reference aethalometer AE33. The study considers several factors that could influence the monitors' performance, including ambient weather, aerosol composition, loading artifacts, and built-in algorithms. The results show that MA350 and DST present considerable discrepancies to the reference instrument, mainly occurring at lower concentrations (0–500 ng/m3) and higher concentrations (2500–8000 ng/m3), respectively. These discrepancies were likely caused by the anomalous noise of MA350 and the loading artifacts of DST. The study also suggests that the ambient environment has limited influence on the monitors' performance, but loading artifacts and accompanying compensation algorithms can result in unrealistic data. Based on the evaluation, the study suggests that C12 is the best choice for unsupervised field measurement, DST should be used in scenarios where frequent maintenance is available, and MA350 is suitable for research purposes with post-processing applicable. The study highlights the importance of assigning portable BC monitors to appropriate applications and the need for optimized real-time compensation algorithms. [Display omitted] [ABSTRACT FROM AUTHOR]

In 2013, several tombs were discovered and excavated in Southeastern Beijing, China, yielding various burial products. Among these were pottery towers, a representative artifact of the Han Dynasty rarely found in the area. Many studies on architectural aspects, such as construction type and construction situation, have been conducted based on the excavated pottery towers, but only a few have examined their raw materials or pigments. In this study, black, white, and red pigments were identified as carbon black, calcite, and cinnabar, respectively, through a multi-analysis approach. The manufacturing method of the pigment was established based on the crystal form and particle size of the pigment, by factoring in the pigment characteristics, which cannot be distinguished by component analysis and crystal structure analysis. We recommend that a continuous database be prepared and used in the future, not only for an interpretation of ancient pigments but also to identify the factors to be considered (physical characteristics, such as pigment particle size among others) when estimating the manufacturing process and conservation treatment. [ABSTRACT FROM AUTHOR]

Black carbon (BC) aerosols in the atmosphere play a significant role in climate systems due to their strong ability to absorb solar radiation. The lifetime of BC depends on atmospheric transport, aging and consequently on wet scavenging processes (in-cloud and below-cloud scavenging). In this study, sequential rainwater samples in eight rainfall events collected in 2 mm interval were measured by a tandem system including a single particle soot photometer (SP2) and a nebulizer. The results showed that the volume-weighted average (VWA) mass concentrations of refractory black carbon (rBC) in each rainfall event varied, ranging from 10.8 to 78.9 µg/L. The highest rBC concentrations in the rainwater samples typically occurred in the first fraction from individual rainfall events. The geometric mean median mass-equivalent diameter (MMD) decreased under precipitation, indicating that r BC with larger sizes was relatively aged and preferentially removed by wet scavenging. A positive correlation (R 2 = 0.73) between the VWA mass concentrations of r BC in rainwater and that in ambient air suggested the important contribution of scavenging process. Additionally, the contributions of in-cloud and below-cloud scavenging were distinguished and accounted for 74% and 26% to wet scavenging, respectively. The scavenging ratio of rBC particles was estimated to be 0.06 on average. This study provides helpful information for better understanding the mechanism of rBC wet scavenging and reducing the uncertainty of numerical simulations of the climate effects of rBC. [Display omitted] [ABSTRACT FROM AUTHOR]

Black carbon (BC), an important component of atmospheric aerosol, plays a significant role in regional climate, hydrological cycle, variation of monsoon rainfall, and human health. The 40-year detailed atmospheric BC over China from 1981 to 2020 is systematically investigated through the MERRA-2 reanalysis dataset. MERRA-2 BC generally showed a good correlation (R = 0.68) compared with 673 monthly samples from ground-based observation at 35 stations around China. The overall annual average of MERRA-2 BC concentration over China is 1.15 μg/m3, with a fast growth rate during 1981–2007 and a relatively slow decrease after that. The winter season has the highest mean concentration of BC, followed by autumn and spring, whereas summer shows relatively weaker values. The order of annual average BC concentrations during 1981–2020 is Beijing-Tianjin-Hebei region (BTH, 4.02 μg/m3) > Sichuan Basin (SB, 3.94 μg/m3) > Yangtze River Delta (YRD, 2.68 μg/m3) > Pearl River Delta (PRD, 1.47 μg/m3). The monthly mean BC concentrations over the BTH, YRD, PRD and SB are estimated to be smallest 3.18 μg/m3 in May, 1.94 μg/m3 in August, 0.82 μg/m3 in July, 3.04 μg/m3 in June, respectively, whilst largest consistently in December with 5.09 μg/m3, 3.83 μg/m3, 2.12 μg/m3, and 5.41 μg/m3, respectively. Our study indicates the primary potential source areas for BC are concentrated in the research city and its surroundings. Beijing and Chengdu are more BC-polluted areas than Shanghai and Guangzhou. Long-distance, regional transfer from south BTH contributes importantly to BC pollution in Beijing under the influence of prevailing southerly winds. The geographical location of Chengdu causes the transport and accumulation of BC inside the SB. [ABSTRACT FROM AUTHOR]

The mass concentration of atmospheric particulate matter (PM) has been continuously decreasing in the Beijing-Tianjin-Hebei region. However, health endpoints do not exhibit a linear correlation with PM mass concentrations. Thus, it is urgent to clarify the prior toxicological components of PM to further improve air quality. In this study, we analyzed the long-term oxidative potential (OP) of water-soluble PM 2.5 , which is generally considered more effective in assessing hazardous exposure to PM in Beijing from 2018 to 2022 based on the dithiothreitol assay and identified the crucial drivers of the OP of PM 2.5 based on online monitoring of air pollutants, receptor model, and random forest (RF) model. Our results indicate that dust, traffic, and biomass combustion are the main sources of the OP of PM 2.5 in Beijing. The complex interactions of dust particles, black carbon, and gaseous pollutants (nitrogen dioxide and sulfur dioxide) are the main factors driving the OP evolution, in particular, leading to the abnormal rise of OP in Beijing in 2022. Our data shows that a higher OP is observed in winter and spring compared to summer and autumn. The diurnal variation of the OP is characterized by a declining trend from 0:00 to 14:00 and an increasing trend from 14:00 to 23:00. The spatial variation in OP of PM 2.5 was observed as the OP in Beijing is lower than that in Shijiazhuang, while it is higher than that in Zhenjiang and Haikou, which is primarily influenced by the distribution of black carbon. Our results are of significance in identifying the key drivers influencing the OP of PM 2.5 and provide new insights for advancing air quality improvement efforts with a focus on safeguarding human health in Beijing. [ABSTRACT FROM AUTHOR]

PM2.5 (fine) and PM2.5–10 (coarse) samples were collected using a Gent stack filter unit sampler in Xinzhen, Beijing. The 220 samples collected from September 2016 to June 2018 were analyzed by neutron activation analysis (NAA) and Black Carbon meter, and 19 elements were determined. Time series analysis, correlation analysis and enrichment factor analysis were performed on the determined component concentrations. The possible sources and temporal variation of some elements were discussed. In addition, the main pollution elements in the three different pollution events were obtained. Furthermore, the element component characteristics of the coarse and fine particles were determined. Finally, the source and backward trajectory of a heavy sandstorm were analyzed by HYSPLIT. Using neutron activation analysis (NAA) and Black Carbon meter, the concentrations of elements and Black Carbon (BC) were determined. Through the correlation analysis and time series analysis, the possible sources and temporal variation of some elements were discussed. Among them, Al, Ca, Ti and Mg in APM are contributed by soil and surface dust. They have strong correlation and similar temporal trend. The concentrations of these elements have obvious seasonal variations. The concentrations of these elements are high in spring and summer, and low in autumn and winter. [ABSTRACT FROM AUTHOR]

The mixing state of refractory black carbon (rBC) aerosols is regarded as a major uncertainty in climate-forcing assessments. This study measured the size distribution and mixing state of rBC using a single-particle soot photometer in the winter of 2022 at an urban site in Beijing. During the campaign, the mean mass concentration of rBC was 0.79 ± 0.63 μg m−3, much lower than that observed in Beijing in the winter of 2013. The number and mass median diameter of the rBC cores were 97 and 200 nm, respectively. The average relative coating thicknesses (RCT) of rBC-containing particles was 1.45 ± 0.27 and average light absorption enhancement (Eabs) was 1.43 ± 0.22. Similar to Eabs, RCT and secondary inorganic aerosols (SIA), especially nitrate, increased with increasing relative humidity. This suggests that higher SIA mass fraction in aerosol with a higher relative humidity in the environment results in a thicker coating and black carbon ageing, thus enhancing light absorption. RCT and Eabs increased rapidly with the increase of PM 1 loading but increased slowly when the PM 1 mass concentration exceeded 60 μg m−3. This indicates that a further increase in the NR-PM 1 species at high PM loading does not increase the thickness of the coatings; therefore, there is no further increase in Eabs. The effects of the chemical composition of the Eabs obtained using the Lindeman, Merenda, and Gold method showed that nitrate plays a prominent role in the enhancement of light absorption, followed by SOA. The rBC mass concentration exhibited clear day-low and night-high patterns which were influenced by the synergetic effects of the boundary layer and emissions. RCT and Eabs presented similar diurnal variations, peaking in the afternoon, which was consistent with the pattern of SIA. This suggests that the SIA produced via photochemical reactions supports the ageing of black carbon-containing particles, leading to light-absorption enhancement. The back-trajectory analysis showed the highest values of rBC mass concentration, RCT, and Eabs appeared in the S cluster suggested that the rBC-containing particles transported from south Beijing were more aged with a thicker coating. While the rBC-containing particles from northern and northwestern Beijing had lower RCT and Eabs values. • Nitrate is the dominant contributor to the coatings on BC and prominent role in light-absorption enhancement. • RCT and Eabs increased rapidly as PM 1 loading increased, but slowly when the PM 1 mass concentration exceeded 60 μg m−3. • The rBC- containing particles transported from south Beijing are more aged with a thicker coating. • ∼15% of the NR-PM 1 mass was bound to BC particles. [ABSTRACT FROM AUTHOR]

The complex particle morphology of black carbon (BC) induces considerable uncertainties in constraining its optical properties. In particular, the diversity of how the BC core and coating are combined is yet to be resolved due to the lack of direct ambient quantification. In this study, by concurrent measurements of the electrical mobility diameter (Dm) and optical volume‐equivalent diameter (Dve), the dynamic shape factor (χ = Dm/Dve) of ambient BC‐containing particles at different mixing states was quantified for the first time. BC in urban Beijing showed a widely distributed χ of 1.4 ± 0.43. Particles with larger refractory BC (rBC) cores showed higher non‐sphericity and higher χ. A ten‐fold increase in the volume ratio of the coating over rBC (VR) could decrease the fraction of fractal BC by 36%. This study proposed a χ‐VR space to describe the particle shape, which is able to include all ambient quantified BC morphologies in optical model. Plain Language Summary: Black carbon (BC) is an important short‐lived light‐absorbing aerosol component in the atmosphere. Its optical properties are complicated by the complex particle morphology, such as the non‐BC substances associated with it and the combination of BC and non‐BC substances within particle. The previous quantification of particle morphology could not distinguish the information specifically for ambient BC, nor the single BC particle characterization can represent full diversities for all particles. This study used concurrent measurements of volume‐equivalent and mobility diameter of BC‐containing particles (BCc) to characterize the coating content and particle shape online for all BC particles in the ambient environment. As a result, we can include all the measured particle morphology information in optical models. Particles with larger BC cores showed higher non‐sphericity, with a greater discrepancy between the measured absorbing properties and that calculated by the Mie theory. Key Points: The morphology of ambient black carbon‐containing particles was characterized by volume‐equivalent and mobility diameter measurementsBlack carbon with higher coatings showed more spherical shapesA space using coatings and particle shape was developed to incorporate morphology information for all black carbon‐containing particles [ABSTRACT FROM AUTHOR]

Under the influence of Coronavirus Disease 2019 (COVID-19), China conducted a nationwide lockdown (LD) which significantly reduced anthropogenic emissions. To analyze the different impacts of COVID-19 on black carbon (BC) in the two representative regions in China, one-year continuous online measurements of BC were conducted simultaneously in Beijing and Tibet. The average concentration in the LD period was 20% higher than that in the pre-LD period in Beijing, which could be attributed to the increase of transport from southwestern neighboring areas and enhanced aged BC. In contrast to megacity, the average concentration of BC in Tibet decreased over 70% in the LD period, suggesting high sensitivity of plateau background areas to the anthropogenic emission reduction in South Asia. Our study clearly showed that BC responded very differently in megacity and background areas to the change of anthropogenic emission under the lockdown intervention. Plain Language Summary China has been influenced by Coronavirus Disease 2019 (COVID-19) in 2020 and the nationwide lockdown (LD) caused emission reduction from human activities. As an important component of PM2.5, black carbon (BC) can absorb light and effect the climate. It is essential to analyze the different impacts of COVID-19 on BC in the two representative regions in China. In this study, BC was measured simultaneously in Beijing and Tibet. The average concentration in the LD was 20% higher than that in the pre-LD period in Beijing, which could be attributed to the increase of transport from southwestern neighboring areas and enhanced aged BC. In contrast to megacity, the average concentration of BC in Tibet decreased over 70% in the LD period, which was mainly the result of the anthropogenic emission reduction in South Asia. Our study clearly showed that BC responded very differently in megacity and background areas to the change of anthropogenic emission, which could help to form better and more specific control strategies for BC under representative atmospheric environment in China. [ABSTRACT FROM AUTHOR]

Considering human activities are the most direct and important factors leading to the accumulation and loss of soil black carbon (BC), a detailed understanding of soil BC in different functional zones and reasonable soil management are the keys to determine whether soil is the carbon source or carbon sink. In this study, carbon concentrations and isotope compositions of black carbon (BC%, δ13CBC) and organic carbon (OC, δ13COC) were determined in topsoil from different functional zones (roadside grass verges, parks, residential areas, mines, arable lands, woodlands and wastelands) in urban and suburban of Beijing, China. The organic carbon (OC) content in soils of the urban area (averaging 1.67%) is higher than in suburban areas (averaging 1.05%). Black carbon is not evenly distributed across different functional zones, but is more concentrated and variable in urban areas (0.11–2.43%, averaging 0.73%) than in suburban areas (0.03–0.70%, averaging 0.18%). The ratios of BC% to OC% in suburban areas (0.04–0.40) are smaller than in urban areas (0.15–0.98). The δ13CBC of topsoil (–26.35...–20.85‰) reflects that coal combustion has a strong impact on soil BC accumulation in Beijing. The carbon isotope differences between OC and BC of the suburban and urban topsoils are positive (averaging +0.56‰) and negative (averaging –0.41‰), respectively. This suggests that urban areas are seriously influenced by human activities which lead to a large amount of fossil fuel combustion, but suburban areas have received a uniform deposition of atmospherically transported finer BC aerosols. [ABSTRACT FROM AUTHOR]

The mass concentration, size distribution and mixing state of refractory black carbon (rBC) particles, together with other pollutants and meteorological variables, were observed at a station with a height of 528 m above ground to understand source of rBC particles over Beijing. Here we present observational evidences that regional transported rBC is an important source of rBC in high layer over Beijing. In our observations, the mass concentration of rBC increased from 1.0 μg m−3 to 4.6 μg m−3 during period with strong regional transport of pollutants, but decreased to 1.8 μg m−3 when regional transport weakened. Such trend was different with local emitted NO x , but consistent with regional transported SO 2. Further analyses indicated that the transported rBC particles were highly aged; the ratio of "thickly" coated rBC in total rBC (f BC) increased from 52.4% to 71.3% during period with strong regional transport, and then decreased slightly to 66.9% when regional transport weakened, likely caused by supplement of freshly emitted local BC particles. The aged rBC particles own enhanced light absorbing capacity, which may exert more important role in weakening atmospheric diffusion capacity and aggravating surface haze pollution, and hence should be concerned in future pollution mitigation. • Regional transported rBC is an important source of rBC in high layer over Beijing. • The transported rBC in high layer is highly aged. • The aged rBC owns enhanced light absorbing capacity. [ABSTRACT FROM AUTHOR]

Atmospheric loading of black carbon aerosols influences air quality and visibility, and their mixing state and aerosol chemistry were sensitive to both emission scenarios and regional transport. In this study, the aerodynamic size-resolved mixing state of refractory black carbon aerosols (rBC) was investigated using a novel tandem system consisting of an aerodynamic aerosol classifier (AAC), a single particle soot photometer (SP2), and single-particle-aerosol mass spectrometry (SPA-MS) during the XXIV Olympic Winter Games (OWG) at an urban site in Beijing. Particles with aerodynamic diameter (D ae) of 200 nm and 300 nm were selected by AAC to focus on the effect of relative differences in morphology on the coating thickness, coating compositions, and optical properties of rBC particles. We found that rBC-containing particles with D ae of 300 nm were characterized by a rBC core with a count median diameter (CMD) of 108 ± 4 nm that typically have regular morphology (χ : m e a n ∼ 1) , higher relative coating thickness (RCT: mean ∼1.9), and strong light absorption enhancement (E abs : mean ∼1.5). The rBC-containing particles with D ae = 200 nm normally had irregular shapes (χ : m e a n ∼ 1.4) and weak E abs (E abs : mean ∼1.37). Classification based on air mass clustering and air pollution level revealed that the coating thickness of rBC particles only exhibited unimodal patterns under clean air conditions and distinct bimodal distributions under heavy pollution conditions, implying multiple origins of rBC particles, even during OWG periods. The coating thickness and E abs of rBC particles were greater when influenced by the higher RH air from east. Furthermore, the chemical compositions of the rBC coating quantitatively determined by SPA-MS were used to estimate the possible origins of the D ae = 300 nm, featured by a thicker coating thickness and stronger light absorption enhancement. Our results showed that rBC particles were primarily mixed with organics, nitrate, and sulfate during the XXIV OWG period. The organic components have a limited role in increasing rBC coatings under polluted conditions, while the alkali metal ions (K and Na) associated with traffic emissions and the secondary inorganic species favor the formation of thick coatings. Higher RH makes limited contributions to rBC mixed with sulfate and organics only (BCOC*_S) and pure BC. The relatively fresh BC could directly mix with organics and sulfate at low RH levels while evolving to mix with nitrate at high RH conditions. In addition to high concentrations of locally emitted precursors and high RH that tend to form thick coatings of nitrate-related rBC aerosols, secondary transport from the west and southwest also contributes to rBC aerosols mixed with nitrate with relatively thick coatings. • rBC with an aerodynamic diameter (D ae) of 300 nm typically have regular morphology. • rBC of regular shape(D ae = 300 nm)has thicker coatings and stronger absorption enhancement. • During the OWG, rBC particles were primarily mixed with organics, nitrate and sulfate. • rBC particles had multiple sources, even in the OWG periods. • The organic components have a limited role in increasing rBC coatings under polluted conditions. [ABSTRACT FROM AUTHOR]

Biomass burning (BB) is an important source of brown carbon (BrC) and black carbon (BC), which are two key highly absorbent substances in atmospheric particles and can have a substantial positive impact on the climate radiative forcing. This study presents the light absorption properties of BC and BrC in PM2.5 during the winter in Beijing, with a discussion on the regional transportation of the light absorption of BC and BrC. Relatively high levels of the light absorption coefficient (Abs λ) of BC, BrC, and the chemical compounds were found during haze episodes. The average Abs BC at λ = 880 and Abs BrC at λ = 370 during the haze period were as high as 4.4 and 2.9 times higher than those during the clean periods. The biomass burning tracer levoglucosan was significantly correlated with Abs BC880 (R 2 = 0.53, P < 0.001), Abs BrC370 (R 2 = 0.47, P < 0.001) and Abs BC(BB) (R 2 = 0.69, P < 0.001). The average contributions of biomass burning to organic carbon (OC) and Abs BC were 33% and 48%, respectively, indicating that biomass burning was an important source of light-absorbing substances in the atmosphere. Concentration-weighted trajectory (CWT) analyses using TrajStat software also demonstrated that regional transport of biomass burning emissions from the northwestern and southwestern areas, which cover the intense fire spots from VIIRS, had a considerable influence on the light absorption properties of PM 2.5 and even haze formation in Beijing during the winter. • Fairly high levels of the Abs BC and Abs BrC found during haze episodes. • Light absorption of BrC gave equal roles to that of BC near the UV–Vis band but was dominant at visible wavelengths. • Regional biomass burning was an important source for light absorbing substance in PM 2.5 during winter in the North China Plain region. [ABSTRACT FROM AUTHOR]

Due to the lack of black carbon (BC) measurement data in some cases, elemental carbon (EC) is often used as a surrogate of BC, with a simple assumption that they are interchangeable. Such assumption will inevitably lead to uncertainties in radiative forcing estimation and health impact assessment. In order to quantitatively and systematically evaluate the relationship between BC and EC as well as factors responsible for their difference, 3-year collocated equivalent BC (eBC) and EC measurements with 1-h resolution were performed in Beijing, China continuously from 2016 to 2019. EBC concentration was measured by the multi-wavelength aethalometer (AE-33) based on optical analysis, while EC concentration was determined by semi-continuous OC/EC analyzer with thermal-optical method. The results showed that around 90% of eBC concentration was higher than that of EC, with average difference between eBC and EC as 1.21 μg m−3 (accounting for 33% of average eBC in Beijing). EBC and EC concentrations exhibited strong correlation (r = 0.90) during the whole study period, but the slopes (or eBC/EC ratio) and correlation coefficients varied across seasons (spring: 1.67 and 0.94; summer: 0.91 and 0.65; fall: 1.15 and 0.88; winter: 1.09 and 0.91, respectively). Based on the information from shell/core ratios by Single Particle Soot Photometer (SP2), source apportionment results by positive matrix factorization model, and chemical composition of PM 2.5 , the differences between eBC and EC concentrations were found to be primarily related to BC aging process and secondary components as evidenced by strong positive correlation with secondary species (e.g., secondary organic carbon and nitrate). This study provided seasonal specific conversion factors of eBC and EC in Beijing and helpful reference for other areas, which will contribute new knowledge of carbonaceous aerosol and reduce uncertainty in assessing future climate change and health studies of BC. • About 90% of eBC mass were higher than EC in Beijing based on 3-year measurement. •EBC and EC were strongly correlated whereas eBC/EC ratios varied with season. •The difference between eBC and EC was related to BC aging and secondary species. [ABSTRACT FROM AUTHOR]

In Beijing, the probability of snowfall is decreasing as a result of global warming. At the same time, Beijing has suffered severe air pollution. In this paper, the concentration and particle size characteristics of BC (Black Carbon) in snow during the winter of 2015 in Beijing were analyzed by the SP2 method. The average concentration of BC in snow meltwater in Beijing is 82 ng/mL, with a minimum value of 62.9 ng/mL and a maximum of 210.6 ng/mL. The BC particle size in snow and ice in the Beijing area is mostly concentrated in the range of 70–400 nm. After log-normal, the BC particle size above 600 nm is still small, which should be closely related to the nature of the local BC emission source. The concentration of BC in snow is highly susceptible to meteorological conditions and local pollution levels. When Beijing is under the control of the east wind or the southeast wind, aerosols in the urban areas can easily accumulate in the northwestern mountains and then settle or participate in the snowfall process, resulting in an increase in BC aerosol accumulation in the snow, thus further changing the optical properties of snow in the Beijing area. [ABSTRACT FROM AUTHOR]