Quantifying the Light-Absorption Properties and Molecular Composition of Brown Carbon Aerosol from Sub-Saharan African Biomass Combustion.

Sub-Saharan Africa is a hotspot for biomass burning (BB)-derived carbonaceous aerosols, including light-absorbing organic (brown) carbon (BrC). However, the chemically complex nature of BrC in BB aerosols from this region is not fully understood. We generated smoke in a chamber through smoldering combustion of common sub-Saharan African biomass fuels (hardwoods, cow dung, savanna grass, and leaves). We quantified aethalometer-based, real-time light-absorption properties of BrC-containing organic-rich BB aerosols, accounting for variations in wavelength, fuel type, relative humidity, and photochemical aging conditions. In filter samples collected from the chamber and Botswana in the winter, we identified 182 BrC species, classified into lignin pyrolysis products, nitroaromatics, coumarins, stilbenes, and flavonoids. Using an extensive set of standards, we determined species-specific mass and emission factors. Our analysis revealed a linear relationship between the combined BrC species contribution to chamber-measured BB aerosol mass (0.4-14%) and the mass-absorption cross-section at 370 nm (0.2-2.2 m2 g-1). Hierarchical clustering resolved key molecular-level components from the BrC matrix, with photochemically aged emissions from leaf and cow-dung burning showing BrC fingerprints similar to those found in Botswana aerosols. These quantitative findings could potentially help refine climate model predictions, aid in source apportionment, and inform effective air quality management policies for human health and the global climate.

Enhanced Light Absorption and Radiative Forcing by Black Carbon Agglomerates.

The climate models of the Intergovernmental Panel on Climate Change list black carbon (BC) as an important contributor to global warming based on its radiative forcing (RF) impact. Examining closely these models, it becomes apparent that they might underpredict significantly the direct RF for BC, largely due to their assumed spherical BC morphology. Specifically, the light absorption and direct RF of BC agglomerates are enhanced by light scattering between their constituent primary particles as determined by the Rayleigh-Debye-Gans theory interfaced with discrete dipole approximation and recent relations for the refractive index and lensing effect. The light absorption of BC is enhanced by about 20% by the multiple light scattering between BC primary particles regardless of the compactness of their agglomerates. The resulting light absorption agrees very well with the observed absorption aerosol optical depth of BC. ECHAM-HAM simulations accounting for the realistic BC morphology and its coatings reveal high direct RF = 3-5 W/m2 in East, South Asia, sub-Sahara, western Africa, and the Arabian peninsula. These results are in agreement with satellite and AERONET observations of RF and indicate a regional climate warming contribution by 0.75-1.25 °C, solely due to BC emissions.

Effect of Fu Yan Qing prescription on pelvic effusion, mass absorption and microenvironment of pelvic blood stasis in patients with sequelae of pelvic inflammatory disease of accumulation of dampness heat and blood stasis type.

Objective: To investigate the effect of Fu Yan Qing prescription on sequelae of pelvic inflammatory disease of accumulation of dampness heat and blood stasis type. Methods: Total 80 patients with sequelae of sequelae of pelvic inflammatory disease of accumulation of dampness heat and blood stasis type were admitted to Baoding No.1 Central Hospital from December, 2018 to April, 2020 and divided into two groups according to the random number table, with 40 cases in each group. Patients in the control group were treated with conventional western medicine, while patients in the observation group were treated with Fu Yan Qing prescription orally. The clinical efficacy, the changes of traditional Chinese medicine (TCM) syndromes, local sign scores, visual analog scale (VAS) of pain, pelvic mass size, pelvic fluid volume and uterine blood flow parameters of the two groups before and after treatment were observed and compared, and the safety of the two groups was evaluated. Results: The total efficacy after treatment in the observation group was 87.5%, which was significantly higher than that of 67.5% in the control group (p<0.05). The TCM syndrome scores, local signs scores, pain scores, size of pelvic mass and pelvic effusion in both groups decreased significantly after treatment (p<0.05), PSV indexes of the two groups were significantly increased after treatment (p<0.05), and these changes were even more pronounced in the observation group (p<0.05). Compared with before treatment, PI and RI indexes of the observation group were significantly decreased after treatment (p<0.05). The observation group experienced an adverse reaction in 7.5% cases considerably lower than the 27.5% of the control group (p<0.05). Conclusion: Fu Yan Qing prescription is a safe and reliable treatment for patients with sequelae of pelvic inflammatory disease of accumulation of dampness heat and blood stasis type. It is worth promotion in clinical practice.

Mass Absorption Efficiency of Black Carbon from Residential Solid Fuel Combustion and Its Association with Carbonaceous Fractions.

Black carbon (BC) emissions, derived primarily from incomplete fuel combustion, significantly affect the global and regional climate. Mass absorption efficiency (MAE) is one important parameter in evaluating the climate impacts of BC. Here, values and variabilities in the MAE of BC (MAEBC) from real-world residential emissions were investigated from a field campaign covering 163 burning events for different fuel-stove combinations. MAEBC (average: 12 ± 5 m2/g) was normally distributed and varied greatly by 2 orders of magnitude. Statistically significant differences in MAEBC were found for various fuels, while no significant differences were observed among different stoves. The fuel difference explained 72 ± 7% of the MAEBC variation. MAEBC did not correlate with the modified combustion efficiency but positively correlated with the ratio of organic carbon (OC) to elemental carbon (EC) and negatively correlated with char-EC. The OC/EC ratio was not always lower in coal emissions in comparison to biomass burning emissions. Coal- and biomass-burning emissions had different profiles of carbon fractions. Char-EC, OC, OC/EC, and char-EC/soot-EC can explain 68.7% of the MAEBC variation, providing the potential for predicting MAEBC from the carbon fractions, since they are more commonly measured and available.

Polycyclic Aromatic Carbon: A Key Fraction Determining the Light Absorption Properties of Methanol-Soluble Brown Carbon of Open Biomass Burning Aerosols.

The composition and radiative forcing of light-absorbing brown carbon (BrC) aerosol remain poorly understood. Polycyclic aromatics (PAs) are BrC chromophores with fused benzene rings. Understanding the occurrence and significance of PAs in BrC is challenging due to a lack of standards for many PAs. In this study, we quantified polycyclic aromatic carbon (PAC), defined as the carbon of fused benzene rings, based on molecular markers (benzene polycarboxylic acids, BPCAs). Open biomass burning aerosols (OBBAs) of 22 rainforest plants were successively extracted with water and methanol for the analysis of water- and methanol-soluble PAC (WPAC and MPAC, respectively). PAC is an important fraction of water- and methanol-soluble organic carbon (WSOC and MSOC, respectively). WPAC/WSOC ranged from 0.03 to 0.18, and MPAC/MSOC was even higher (range: 0.16-0.80). The priority polycyclic aromatic hydrocarbons contributed less than 1% of MPAC. The mass absorption efficiency (MAE) of MSOC showed a strong linear correlation with MPAC/MSOC (r = 0.60-0.95, p < 0.01). The absorption Ångström exponent (AAE) of methanol-soluble BrC showed a strong linear correlation with the degree of aromatic condensation of MPAC, which was described by the average number of carboxylic groups of BPCA (r = -0.79, p < 0.01). This result suggested that PAC was a key fraction determining the light absorption properties (i.e., light absorptivity and wavelength dependence) of methanol-soluble BrC in OBBAs.

Low-Voltage Electron-Probe Microanalysis of Uranium.

Electron-probe microanalysis of uranium and uranium alloys poses several problems, such as rapid oxidation, large poorly constrained correction factors, and a large number of characteristic x-ray lines. We show that U-metal can grow 10 nm of oxide within ~20 s of air exposure, increasing to 15­20 nm within a few minutes, which can produce a 30% quantification error at 5 kV. A 15 nm carbon coating on the UO2 reference material also produces an ~30% quantification error of the uncoated but surface oxidized U sample at 5 kV. Correcting for both the coating and oxide improved the analysis accuracy to better than ±1% down to 7 kV and ~2% at 5 kV, but the error increases strongly below this. The measurement of C in U identified a previously unreported U N6­O4 line interference on the C Kα peak, which can produce over 1% error in the analysis total. Oxide stoichiometry was demonstrated to have only a small impact on quantification. The measurement of the O Kα and U Mα mass absorption coefficients in U as 9,528 and 798 cm2/g, respectively, shows good agreement with recently published values and also produces small differences in a quantification error.

The Impact of Chemical Bonding on Mass Absorption Coefficients of Soft X-rays.

Accurate elemental quantification of materials by X-ray detection techniques in electron microscopes or microprobes can only be carried out if the appropriate mass absorption coefficients (MACs) are known. With continuous advancements in experimental techniques, databases of MACs must be expanded in order to account for new detection limits. Soft X-ray emission spectroscopy (SXES) is a characterization technique that can detect emitted X-rays whose energies are in the range of 10 eV to 2 keV by using a varied-line-spaced grating. Transitions producing soft X-rays can be detected and accurate MACs are required for use in quantification. This work uses Monte Carlo modeling coupled with multivoltage SXES measurements in an electron probe micro-analyzer (EPMA) to compute MACs for the L2,3-M and Li Kα transitions in a variety of aluminum alloys. Electron depth distribution curves obtained by the software MC X-ray are used in a parametrized fitting equation. The MACs are calculated using a least-squares regression analysis. It is shown that X-ray distribution cross-sections at such low energies need to take into account additional contributions, such as Coster­Kronig transitions, Auger yields, and wave function effects in order to be accurate.

Quantification of Olivine Using Fe Lα in Electron Probe Microanalysis (EPMA).

Quantification of first series transition metal Lα X-rays is hampered by absorption and in some cases transition probabilities (fluorescence yields) varying with chemical bonding. Compound mass absorption coefficients for Fe Lα were measured in the olivine solid solution series [Forsterite (Mg2SiO4) to Fayalite (Fe2SiO4)] and the mass absorption coefficients for Fe Lα absorbed by Fe were calculated. The mass absorption coefficients vary systematically between Fo83 and Fo0. Using the measured mass absorption coefficients for both standard and unknown and by correcting for a systematic discrepancy, consistent with varying partial fluorescence yields, a good agreement between calculated k-ratios and measured k-ratios is achieved. The systematic variations allow quantification of unknown k-ratios. The described method of quantification requires modification of matrix correction routines to allow standards and unknowns to have different mass absorption coefficients, and to incorporate solid solution mass absorption coefficients and partial fluorescence yield corrections derived from regression of experimental data.

Field evidence of brown carbon absorption enhancement linked to organic nitrogen formation in Indo-Gangetic Plain.

Atmospheric brown carbon (BrC), a short-lived climate forcer, absorbs solar radiation and is a substantial contributor to the warming of the Earth's atmosphere. BrC composition, its absorption properties, and their evolution are poorly represented in climate models, especially during atmospheric aqueous events such as fog and clouds. These aqueous events, especially fog, are quite prevalent during wintertime in Indo-Gangetic Plain (IGP) and involve several stages (e.g., activation, formation, and dissipation, etc.), resulting in a large variation of relative humidity (RH) in the atmosphere. The huge RH variability allowed us to examine the evolution of water-soluble brown carbon (WS-BrC) diurnally and as a function of aerosol liquid water content (ALWC) and RH in this study. We explored links between the evolution of WS-BrC mass absorption efficiency at 365 nm (MAEWS-BrC-365) and chemical characteristics, viz., low-volatility organics and water-soluble organic nitrogen (WSON) to water-soluble organic carbon (WSOC) ratio (org-N/C), in the field (at Kanpur in central IGP) for the first time worldwide. We observed that WSON formation governed enhancement in MAEWS-BrC-365 diurnally (except during the afternoon) in the IGP. During the afternoon, the WS-BrC photochemical bleaching dwarfed the absorption enhancement caused by WSON formation. Further, both MAEWS-BrC-365 and org-N/C ratio increased with a decrease in ALWC and RH in this study, signifying that evaporation of fog droplets or bulk aerosol particles accelerated the formation of nitrogen-containing organic chromophores, resulting in the enhancement of WS-BrC absorptivity. The direct radiative forcing of WS-BrC relative to that of elemental carbon (EC) was ∼19 % during wintertime in Kanpur, and âˆ¼ 40 % of this contribution was in the UV-region. These findings highlight the importance of further examining the links between the evolution of BrC absorption behavior and chemical composition in the field and incorporating it in the BrC framework of climate models to constrain the predictions.

Roles of water-soluble aerosol coatings for the enhanced radiative absorption of black carbon over south asia and the northern indian ocean.

Black Carbon (BC), formed by incomplete combustion, absorbs solar radiation and heats the atmosphere. We investigated the enhancement in optical absorption of BC due to coatings of water-soluble (WS) species in the polluted South Asian atmosphere. The BC Mass Absorption Cross-section (MAC; 678 nm) was estimated before and after removal of the WS components. Wintertime samples were collected from three South Asian receptor observatories intercepting large-footprint outflow: Bangladesh Climate Observatory Bhola (BCOB; integrating outflow of the Indo-Gangetic Plain), Maldives Climate Observatories at Hanimaadhoo (MCOH) and at Gan (MCOG), both reflecting outflow from the South Asian region. The ambient MAC observed at BCOB, MCOH and MCOG were 4.2 ± 1.4, 7.9 ± 1.9 and 7.1 ± 1.5 m2 g-1, respectively. The average enhancement of the BC MAC due to WS coatings (i.e., ws-EMAC) was identical at all three sites (1.6 ± 0.5) indicating that the anthropogenic aerosols had already evolved to a fully coated morphology at BCOB and/or that subsequent aging involved two compensating evolution processes of the coating. Inspecting the key coating component sulfate; the sulfate-to-BC ratio increased threefold when transitioning from BCOB to MCOH and by about 1.5 times from BCOB to MCOG. Conversely, both WS organic carbon (WSOC)/BC and water-insoluble OC (WIOC)/BC ratios declined with distance: WSOC/BC diminished by 84 % from BCOB to MCOH and by 80 % from BCOB to MCOG, while WIOC/BC dropped by about 63 % and 59 %, respectively. Such declines in WSOC and WIOC reflect a combination of photochemical oxidation and more efficient washout of OC compared to BC. The observed changes in the SO42-/BC and WSOC/BC ratios across South Asia highlight the significant impact of aerosol composition on the optical properties of Black Carbon (BC). These findings emphasize the need for detailed studies on aerosol composition to improve climate models and develop effective strategies for reducing the impact of anthropogenic aerosols on the climate.

Creating Biomimetic Central-Radial Skeletons with Efficient Mass Adsorption and Transport.

Porous skeletons play a crucial role in various applications. Their fundamental significance stems from their remarkable surface area and capacity to enhance mass adsorption and transport. Freeze-casting is a commonly utilized methodology for the production of porous skeletons featuring vertically aligned channels. Nevertheless, the resultant single-oriented skeleton displays anisotropic mass transfer characteristics and suboptimal mechanical properties. Our investigation was motivated by the intricate microstructures observed in botanical organisms, leading us to devise an advanced freeze-casting methodology. A novel central-radial skeleton with significantly enhanced capabilities has been successfully engineered. The central-radial architecture demonstrates superior refinement and uniformity in its pore structure, featuring an axial mass transfer axis and meticulously arranged radial channels. This microstructure endows the porous skeleton with a higher compression resilience, superior adsorption rate, and structural maintenance capacity. Through a rigorous examination of the thermal conductivity of skeleton-filled composites coupled with comprehensive COMSOL simulations, the exceptional characteristics of this unique structural arrangement have been definitively ascertained. Furthermore, the efficacy of implementing this skeleton in chip cooling and photothermal conversion has been convincingly substantiated. Our pioneering method of microstructure preparation, employing freeze-casting, holds immense potential in expanding its applicability and inspiring innovative concepts for the advancement of novel structures.

Characterization and source apportionment for light absorption amplification of black carbon at an urban site in eastern China.

The mass absorption efficiency (MAE) of black carbon (BC) could be amplified by both internal mixing and the lensing effect from non-absorbing coating, which could intensify the global warming effect of BC. In this study, a two-year-long continuous campaign with measurements of aerosol optical properties and chemical composition were conducted in Nanjing, a typical polluted city in the Yangtze River Delta (YRD) region. Relatively large MAE values were observed in 2016, and the high BC internal mixing level could be the main cause. The strong positive correlation between the ratio of non-absorbing particulate matter (NAPM) over elemental carbon (EC) and the MAE value indicated that the coating thickness of BC largely promotes its light absorption ability. The impacts of chemical component coating on MAE amplification in autumn and winter were greater than in other seasons. Multiple linear regression was performed to estimate the MAE amplification effect by internal mixing and the coating of different chemical components. Nitrate coating had the strongest impact on MAE amplification, followed by organic matter. The effects of organic matter and nitrate coatings on MAE amplification increased with the internal mixing index (IMI). Based on the positive matrix factorization (PMF) model, it was found that large decrease in the contribution of industrial emissions and coal combustion to PM2.5 from 2016 to 2017 was the main cause for MAE reduction. The novel statistical model developed in this study could be a useful tool to separate the impacts of internal mixing and non-absorbing coating.

Mass absorption coefficient in the 200-800 eV region of sp3 carbon atoms measured using self-standing polyethylene thin films.

To experimentally determine the mass absorption coefficient (µ) of a sp3-carbon (C) atom in the soft X-ray region, soft X-ray absorption spectra (XAS) in the 200-800 eV and C K regions of 200-nm-thick self-standing polyethylene (PE) films were measured in the transmission and total electron yield (TEY) modes. PE films were prepared by a spin-coating method. Their experimentally measured thickness and density are 200 nm and 0.920 g/cm3, respectively. Soft X-ray absorption measurements were performed in beamline BL-6.3.2 at the Advanced Light Source. Although surface oxygen can be slightly observed in the O K and C K regions in TEY-XAS, it cannot be observed in absorbance-XAS. The absorbance-XAS profiles agree well with the calculated profiles, except in the C K threshold. Hence, it can be confirmed that the absorption-XAS measurements are achieved. From the absorbance, µ of sp3-C in PE is 7 × 104 cm2/g near 288 eV and 294 eV.

A direct method to quantify methanol-soluble organic carbon for brown carbon absorption studies.

The current research provides a newly developed method to quantify methanol-soluble organic carbon (MeS_OC) in aerosol samples. This analytical procedure allows an accurate separation of MeS-OC component, which is critical for the calculation of mass absorption efficiency (MAE) of ambient Brown Carbon (BrC) and consequently its climate relevant potential. The method includes extraction, filtering and condensation stages, leading to the preparation of a highly concentrated product in which MeS-OC can be precisely quantified by a Sunset Carbon Analyzer in a single analysis step. This method can be applied on aerosol collected using either high or low volume samplers, since a relatively small filter area is required for the determination. Furthermore, it eliminates any misestimation of the MeS-OC mass that may appear in other reported techniques that don't seem to include the precise separation of methanol-soluble fraction in their quantification process.•The mass quantification of methanol-soluble organic carbon is essential, contributing up to 50% to the absorptivity of organic aerosol (BrC) at shorter wavelengths.•The method provides a direct measurement of methanol-soluble aerosol components, resolving any potential uncertainties of previously applied methods.•The adoption of this direct quantification approach leads to a rationalization of past MAE estimates for BrC with implications for radiative transfer models.

Light absorption properties of brown carbon from biomass burning emissions.

A laboratory-scale experiment was conducted to determine the light absorption properties of brown carbon (BrC) produced from the incomplete combustion of 14 different biomasses. Particulate matters (PM) emitted from biomass burning were collected on the quartz fiber filters with a low volume sampler. BrC from filter samples was extracted with two different solvents (methanol and water), and absorption characteristics of BrC were determined using a UV-Vis spectrophotometer. The absorption coefficient (babs-BrC), mass absorption efficiency (MAEBrC), absorption angstrom exponent (AAEBrC), and absorbing portion of refractive index (kabs-BrC) were calculated for each biomass from the absorbance of the extracted solution. Methanol-soluble BrC (MeS-BrC) showed higher absorbance than water-soluble BrC (WS-BrC) in all biomasses. MeS-BrC has higher babs-BrC than WS-BrC, suggesting that the rate of light absorption on BrC extracted in methanol was higher. The absorption coefficients (babs-BrC) were varied among biomasses-rain tree had the highest value of babs-BrC, whereas jute stick had the lowest. The mass absorption efficiency of BrC (MAEBrC) was evaluated in both water and methanol extracts, and it was found that the MAEBrC for MeS-BrC in the biomasses was greater than that of WS-BrC. The highest MAEBrC value (13.02 m2g-1) was identified in the jackfruit tree, whereas the lowest MAEBrC value (0.1 m2g-1) was observed in the jute stick. The absorption angstrom exponent (AAE) of both WS-BrC and MeS-BrC was determined which represents the light absorption capacity of the aerosol particles. The highest AAE value was found in cow dung, and the lowest was found in rain tree. The increasing pH of the WS-BrC solution increased its optical absorption. However, this study revealed that the light absorption properties of brown carbon emitted from commonly used biomasses were varied significantly.

Source attribution of black and Brown carbon near-UV light absorption in Beijing, China and the impact of regional air-mass transport.

Black and Brown Carbon (BC, BrC) are key parameters of climate forcing, yet significant challenges exist assigning emission source contributions to light-absorption by carbonaceous aerosols. Additionally, BC and BrC emissions add to extreme air pollution events in Chinese mega-cities, which harm human health and detract from the natural and built environment. To address these concerns, the ability to estimate atmospheric light absorption related to emission sources and global inventories is a highly valuable tool for climate modelers and policy makers. Three months of BC and BrC data was collected using an Aethalometer in parallel to PM2.5 filter sampling during a stringent emission controls period and post controls period, including during the regional heating season. In this study reconstructed 370 nm wavelength absorption was calculated by applying source specific Mass Absorption Cross-Sections to PMF apportioned EC and OC results. Reconstructed absorption showed good agreement with the ambient measured absorption for both BC and BrC. In Beijing, the major contributor to near-UV absorption was mobile sources, which accounted for 45-54% of absorption by BC and 14-18% by BrC. BrC absorption from secondary aerosols, biomass burning, and soil dust was also estimated, with these sources contributing from 1 to 9% individually. Meteorological cluster analysis showed that air mass origin did not impact the absorption reconstruction and that the highest regional contribution to near-UV light absorption originated primarily in areas south and east of Beijing. The study shows ambient near-UV light absorption can be predicted using BC and BrC MAC values from sources. However, the current number of multi-wavelength and source specific BrC MAC values reported in the literature is limited. The reconstruction approach allows for a more robust method of assigning light absorption to source categories, allowing the expansion of aethalometer derived BrC apportionment to multiple sources, including biomass burning.

Effects of NO2 and RH on secondary organic aerosol formation and light absorption from OH oxidation of ο-xylene.

Ο-xylene is an important aromatic volatile organic compound (VOC) in the atmosphere over urban areas. In this work, the effect of nitrogen dioxide (NO2) concentration and relative humidity (RH) on the mass concentration of secondary organic aerosols (SOA) formed from ο-xylene OH oxidization was investigated in a photooxidation chamber. The ο-xylene SOA mass concentration increased from 54.2 µg m-3 to 127.2 µg m-3 during dry conditions, but decreased from 177.7 µg m-3 to 146.5 µg m-3 during high RH conditions when the initial NO2 concentration increased form 0 ppbv to about 900 ppbv. An increase in the ratio of [NO3-]/[Org] and a decrease in the oxidation state of carbon (OSC) of SOA suggested that acid-catalyzed heterogeneous reaction was responsible for enhancing SOA formation with increasing NO2 concentrations in dry conditions. In contrast, in humid conditions, the high molecular diffusion capacity of SOA could promote the reactivity of OH towards the interior of SOA, and the enhancement of nitrous acid (HONO) formation under high NO2 conditions could promote the SOA aging processes and be responsible for the decreasing trend of SOA formation with NO2. Light absorption by SOA was also measured, and both NO2 and RH enhanced the mass absorption coefficient (MACλ = 365 nm) value for the optical properties of ο-xylene SOA. The highest MACλ = 365 nm value of ο-xylene SOA was 0.89 m2 g-1, observed during humid conditions with an initial NO2 concentration of 862 ppbv, which was 3.9 times higher than in the experiment conducted in the absence of NO2 under dry conditions. The formation of nitrogen-containing organic compounds (NOCs) and humic-like substances (HULIS) were responsible for the increased MACλ = 365 nm values of ο-xylene derived SOA. This study provides new insight into the effect of NO2 on SOA formation through the change in ο-xylene photooxidation under different RH conditions, and the complex effect of multiple environmental factors on SOA formation was also important and should not be ignored.

Deconvolving light absorption properties and influencing factors of carbonaceous aerosol in Shanghai.

Black carbon (BC) and brown carbon (BrC) have intensive impacts on atmospheric visibility and global climate change. In this study, PM2.5 samples were collected at Pudong (PD) and Qingpu (QP) of Shanghai in 2017, and characterized typical organic molecular tracers by gas chromatography-mass spectrometer. The light absorption (Abs) of carbonaceous aerosol and water-soluble organic matter was analyzed by a multi-wavelength thermal/optical carbon analyzer and a long-range ultraviolet-visible spectrophotometer. An improved two-component model integrated with both optical and chemical fingerprints of carbonaceous aerosol was applied to analyze the Abs of BC, water-soluble organic carbon (WSOC) and water-insoluble organic carbon (WISOC), with which the potential influencing factors including emission source and atmospheric aging were investigated. Results indicated that BrC contributed 19% at PD and 16% at QP of the total light absorption of the carbonaceous aerosol at 405 nm wavelength. Meanwhile, AbsWSOC(405)/AbsBrC(405) showed significant seasonal variations (27-50%) at both sites. Positive matrix factorization (PMF) analysis showed that vehicle emissions (60-61%) and biomass combustion (38-39%) were the major contributors to AbsBC(405), while biomass burning (34-40%), nitrate-relevant secondary processes (22-23%), vehicle emissions (18-19%) and biogenic SOA (13-19%) were major contributors to AbsWSOC(405). Hybrid combustion source (94-96%) had a predominant contribution to AbsWISOC(405). Statistical analysis showed that biomass burning had a great impact on the enhancement of AbsWISOC. Absorption Ångström exponent (AAE) and mass absorption efficiency (MAE) of each factor (source) using PMF analysis indicated that WSOC from combustion sources had higher AAEWSOC(350-550) values (8.11 and 8.29 for coal and biomass burning, respectively) and MAEWSOC(365) values (0.63-0.99) compared to other sources. Atmospheric aging process can lower the MAEWSOC(365) value (0.24-0.52). Overall, our study facilitates a better understanding of the relationships among source, optical properties, and atmospheric transformation processes of the carbonaceous aerosols in Shanghai.

Insights into aerosol chemical composition and optical properties at Lulin Atmospheric Background Station (2862 m asl) during two contrasting seasons.

Continental outflows from peninsular Southeast Asia and East Asia dominate the widespread dispersal of air pollutants over subtropical western North Pacific during spring and autumn, respectively. This study analyses the chemical composition and optical properties of PM10 aerosols during autumn and spring at a representative high-altitude site, viz., Lulin Atmospheric Background Station (23.47°N, 120.87°E; 2862 m a.s.l.), Taiwan. PM10 mass was reconstructed and the contributions of major chemical components were also delineated. Aerosol scattering (σsp) and absorption (σap) coefficients were regressed on mass densities of major chemical components by assuming external mixing between them, and the site-specific mass scattering efficiency (MSE) and mass absorption efficiency (MAE) of individual components for dry conditions were determined. NH4NO3 exhibited the highest MSE among all components during both seasons (8.40 and 12.58 m2 g-1 at 550 nm in autumn and spring, respectively). (NH4)2SO4 and organic matter (OM) accounted for the highest σsp during autumn (51%) and spring (50%), respectively. Mean MAE (mean contribution to σap) of elemental carbon (EC) at 550 nm was 2.51 m2 g-1 (36%) and 7.30 m2 g-1 (61%) in autumn and spring, respectively. Likewise, the mean MAE (mean contribution to σap) of organic carbon (OC) at 550 nm was 0.84 m2 g-1 (64%) and 0.83 m2 g-1 (39%) in autumn and spring, respectively. However, a classification matrix, based on scattering Ångström exponent, absorption Ångström exponent, and single scattering albedo (ω), demonstrated that the composite absorbing aerosols were EC-dominated (with weak absorption; ω = 0.91-0.95) in autumn and a combination of EC-dominated and EC/OC mixture (with moderate absorption; ω = 0.85-0.92) in spring. This study demonstrates a strong link between chemical composition and optical properties of aerosol and provides essential information for model simulations to assess the imbalance in regional radiation budget with better accuracy over the western North Pacific.

Diurnal variability in the spectral characteristics and sources of water-soluble brown carbon aerosols over Delhi.

It is well established that light-absorbing organic aerosols (commonly known as brown carbon, BrC) impact climate. However, uncertainties remain as their contributions to absorption at different wavelengths are often ignored in climate models. Further, BrC exhibits differences in absorption at different wavelengths due to the variable composition including varying sources and meteorological conditions. However, diurnal variability in the spectral characteristics of water-soluble BrC (hereafter BrC) is not yet reported. This study presents unique measurement hitherto lacking in the literature. Online measurements of BrC were performed using an assembled system including a particle-into-liquid sampler, portable UV-Visible spectrophotometer with liquid waveguid capillary cell, and total carbon analyzer (PILS-LWCC-TOC). This system measured the absorption of ambient aerosol extracts at the wavelengths ranging from 300 to 600 nm with 2 min integration time and water-soluble organic carbon (WSOC) with 4 min integration time over a polluted megacity, New Delhi. Black carbon, carbon monoxide (CO), nitrogen oxides (NOx), and the chemical composition of non-refractory submicron aerosols were also measured in parallel. Diurnal variability in absorption coefficient (0.05 to 65 Mm-1), mass absorption efficiency (0.01 to 3.4 m-2 gC-1) at 365 nm, and absorption angstrom exponent (AAE) of BrC for different wavelength range (AAE300-400: 4.2-5.8; AAE400-600: 5.5-8.0; and AAE300-600: 5.3-7.3) is discussed. BrC chromophores absorbing at any wavelength showed minimum absorption during afternoon hours, suggesting the effects of boundary layer expansion and their photo-sensitive/volatile nature. On certain days, a considerable presence of BrC absorbing at 490 nm was observed during nighttime that disappears during the daytime. It appeared to be associated with secondary BrC. Observations also infer that BrC species emitted from the biomass and coal burning are more absorbing among all sources. A fraction of BrC is likely associated with trash burning, as inferred from the spectral characteristics of Factor-3 from the PMF analysis of BrC spectra. Such studies are essential in understanding the BrC characteristics and their further utilization in climate models.