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Introduction: Ovarian cancer (OC) is the malignant tumor with the highest mortality among gynecological cancers. Chemotherapy resistance is a major obstacle to OC therapy. Circular RNAs (circRNAs) play crucial roles in cancer development and chemoresistance. However, the role and potential mechanism of has-circ-001567 (circ-VPS13C) in chemoresistance of OC remain unknown. Material and methods: The levels of circ-VPS13C, miR-106b-5p and 14-3-3 zeta (YWHAZ) were detected by quantitative real-time polymerase chain reaction (qRT-PCR) or western blot assay. Cell Counting Kit-8 (CCK-8) assay was used to assess cell viability and calculate the half inhibition concentration (IC50) of cisplatin (DDP). The levels of autophagy-related markers were measured by western blot assay. Cell apoptosis and migration were evaluated by flow cytometry and transwell assay, respectively. The binding relationship between miR-106b-5p and circ-VPS13C or YWHAZ was confirmed by dual-luciferase reporter assay. Xenograft assay was performed to explore the role of circ-VPS13C in vivo. Results: Circ-VPS13C and YWHAZ were up-regulated, while miR-106b-5p was down-regulated in DDP-resistant OC tissues and cells. Knockdown of circ-VPS13C enhanced DDP sensitivity by repressing autophagy in DDP-resistant cells. Circ-VPS13C increased DDP resistance via sponging miR-106b-5p. Moreover, miR-106b-5p directly targeted YWHAZ. Up-regulation of YWHAZ alleviated the decrease in DDP resistance caused by circ-VPS13C depletion. In addition, circ-VPS13C silencing decreased DDP resistance in vivo. Conclusions: Circ-VPS13C knockdown enhanced DDP sensitivity of OC through modulation of autophagy via the miR-106b-5p/YWHAZ axis, providing a new biomarker for improving the efficacy of OC chemotherapy. [ABSTRACT FROM AUTHOR]

The microphysical properties associated with the ice production importantly determine the precipitation rate of clouds. In this study, the microphysical properties including the size distribution and particle morphology of water and ice for stratocumulus during an extratropical cyclone over the northern China were in-situ characterized. Stages of cloud were investigated including young cells rich of liquid water, developing and mature stages with high number concentration of ice particles (Nice). The Nice could reach 300 L-1 at the mature stage, about two orders of magnitudes higher than the primary ice number concentration calculated from ice nucleation. This high Nice occurred at about -5 to -12 ⁰C, spanning the temperature region of Hallett-Mossop process and possible other mechanisms for the secondary ice production (SIP). The Nice was positively associated with the number concentrations of large graupel with diameter (d) > 250 μm and large supercooled droplet (d > 50 μm). The SIP rate was 0.005-1.8 L-1s-1 derived from the measured Nice with known ice growth rate between two sizes. The SIP rate could be produced by a simplified collision-coalescence model within an uncertainty factor of 5, by considering the collection of large droplets by graupel. The collection efficiency between was found to increase when the size of droplet was closer to graupel which may improve the agreement between measurement and model. Importantly, the overall Nice was found to be highly related to the distance to cloud-top (DCT). The level with larger DCT had more abundant rimmed graupels falling from the above level, which promoted the coalescence processes between graupels and droplets, producing a higher fraction of smaller ice through SIP. This seeder-feeder process extended the avalanche SIP at lower temperature up to -14 ⁰C beyond the temperature region of Hallett-Mossop process. The results illustrated the microphysical properties of clouds with convective cells under different stages, which will improve the understanding of the key processes in controlling the cloud glaciation and precipitation process. [ABSTRACT FROM AUTHOR]

The cloud condensation nuclei (CCN) activity of black carbon particles (BC) importantly determines their impacts on cloud microphysics and atmospheric lifetime. This process is crucially determined by the amount of more hygroscopic coating materials BC can acquire during aging process. It remains a challenge for ambient measurements to capture this process and link this with CCN activity of BC. Here by using coupled measurements of size-resolved number concentrations of CCN at configured water supersaturation (SS) and BC24 containing particles (BCc), we are able to directly monitor the droplet activation diameter (D50) and activation fraction of BCc (Fact, BC) in ambient environment. The number concentration of BCc was found to peak at diameter 180-210 nm after acquiring coatings, larger than that for all particles (50-150 nm). This led to that the initially smaller BC can be enlarged and become larger and more hygroscopic, even having higher CCN activities than other particles. The Fact, BC increased from 42% to 69% in number and from 67% to 85% in mass, as SS increased from 0.1% to 0.2%, but tended to reach a plateau when SS>0.2%.Notably, Fact, BC and D50 linearly correlated with equivalent photochemical age, at a rate of +2% per hour and -3nm per hour, respectively. The results suggest BCc from anthropogenic sources can readily serve as CCN at a relatively low SS, and over half of the BC population can be activated in a few hours. This means the surface-sourced BC can efficiently incorporate into clouds and may exert important indirect radiative impacts. [ABSTRACT FROM AUTHOR]

Black carbon (BC, i.e., soot) absorbs radiation and contributes to glacier retreat over the Tibetan Plateau (TP). A lack of comprehensive understanding of the actual mixing state leads to large controversies in the climatic simulation of BC over the TP. In this study, ground-based sampling, electron microscopy analyses, and theoretical calculations were used to investigate the interactions among the liquid-liquid phase separation (LLPS), soot redistribution in secondary particles, and fractal dimension (Df) of soot particles on the eastern rim of the TP. We found that more than half of the total analysed particles were soot-containing particles. One-third of soot-containing particles showed the LLPS phenomenon between organic matter and inorganic aerosols in individual particles, which further induced soot redistribution. The results show that a larger LLPS particle size, thicker organic coating, and smaller soot particles tended to drag soot from the sulfate core into the organic coating. The Df sequence is ranked as externally mixed soot (1.79±0.09) < sulfate-coated soot (1.84±0.07) < organic-coated soot (1.95±0.06). We concluded that the soot redistribution process and high RH both promoted the morphological compaction of soot particles. This study indicates that soot-containing particles experienced consistent ageing processes that induced a more compact morphology and soot redistribution in the LLPS particles on the remote eastern rim of the TP. Understanding the microscopic changes in aged soot particles could further improve the current climate models and evaluations of BC's radiative impacts on the eastern TP and similar remote air. [ABSTRACT FROM AUTHOR]

The light-absorbing organic aerosol (OA), known as brown carbon (BrC), has important radiative impacts, however its sources and evolution after emission remain to be elucidated. In this study, the light absorption at multiple wavelengths, mass spectra of OA and microphysical properties of black carbon (BC) were characterized at a typical sub-urban environment in Beijing. The absorption of BC is constrained by its size distribution and mixing state, being subtracted from total absorption to obtain the absorption of BrC, then by applying the least-correlation of BC absorption with secondary BrC, the absorption contributed by BC, primary BrC and secondary BrC was apportioned. The multi-linear regression analysis on the factorized OA mass spectra indicated the OA from traffic and biomass burning emission contributed to primary BrC. Importantly, the moderately oxygenated OA (O/C=0.62) was revealed to highly correlate with secondary BrC. These OA had higher nitrogen content, in line with the nitrogen-containing functional groups detected by the Fourier transform infrared spectrometer. The photooxidation was found to result in reduced contribution of primary BrC about 20% but enhanced contribution of secondary BrC by 30%, implying the concurrent whitening and darkening of BrC. This provides field evidence that the photochemically produced secondary nitrogen-containing OA can considerably compensate some bleaching effect on the primary BrC, hereby causing radiative impacts. [ABSTRACT FROM AUTHOR]

There has been controversy about the air pollutants emitted from sources closely related to people's daily life (such as cooking, fireworks burning, sacrificial incenses and joss paper burning, and barbecue, named as five missing sources, FMS) impacting the outdoor air quality to what extent. Till now, there is no emission estimation of air pollutants from FMS, as the missing of both activity dataset and emission factors. We attempted to combine the questionnaire data, various statistical data, and data of points of interest to obtain a relatively complete set of activity data. The emission factors (EFs) of carbonaceous aerosols were tested in our lab. Then, the emission inventories of carbonaceous aerosol with the high spatial-temporal resolution for FMS were established firstly, and the spatial-variation trend and driving forces were discussed. From 2000 to 2018, organic carbon (OC) increased from 4268 t to 4919 t. The OC emission from FMS was 1.48-2.18 - of its total emission in China. The emissions of black carbon, element carbon (EC), and brown carbon absorption cross-section (ACSBrC) emissions from FMS were in the ranges of 22.6-43.9 t, 213-324 t, and 14.7-35.6 Gm2, respectively. Their emissions tended to concentrate in special periods and areas. The OC emission intensities in central urban areas were 3.85-50.5 times that of rural areas due to the high density of human activities. While the ACSBrC emissions in rural regions accounted for 63.0-79.5% of the total emission result from uncontrolled fireworks burning. A mass of fireworks burning led to extremely higher ACSBrC and EC emissions on Chinese New Year's eve, as 1444 and 262 times their corresponding yearly average values. Interestingly, significant (p<0.01) correlations between human incomes and pollutant emissions were found, but they were positive (r = 0.94) and negative (r = -0.94) for urban and rural regions, indicating the necessity of regulating human lifestyle and increasing income for urban and rural peoples, respectively. This study provided the first-hand data for identifying the emissions, variation trends and impacting factors of FMS, which is helpful for modeling works on air quality, climate effect, and human health risks at specific periods or regions and for modifying their emission control policies. The data in this work could be found at https://doi.org/10.6084/m9.figshare.19999991.v1 (Cheng et al., 2022). [ABSTRACT FROM AUTHOR]

The secondary production of the oxygenated organic aerosol (OOA) impacts air quality, climate and human health. The importance of various sources in contributing to the OOA loading and associated different aging mechanisms remains to be elucidated. Here we present concurrent observation and factorization analysis on the mass spectra of organic aerosol (OA) by a high-resolution aerosol mass spectrometer and volatile organic compounds (VOCs) by a proton-transfer- reaction mass spectrometer in Wuhan, a megacity in central China during autumntime. The full mass spectra of organics with two principle anthropogenic sources were identified as the traffic and cooking sources, for their primary emission profiles in aerosol and gas phases, the evolutions, and their respective roles in producing OOA and secondary VOCs. Primary emissions in gas and aerosol phases both contributed to the production of OOA. The photooxidation of traffic sources from morning rush-hour caused 2.5-folds increase of OOA mass in a higher oxidation state (O/C=0.72), coproducing gas-phase carboxylic acids; while at night, cooking aerosols and VOCs (particularly acrolein and hexanal) importantly caused the nocturnal formation of oxygenated intermediate VOCs, increasing OOA mass by a factor of 1.7 (O/C=0.42). The daytime and nighttime formation of secondary aerosols as contributed by different sources, was found to be modulated by solar radiation and air moisture respectively. The environmental policy should therefore consider the primary emissions and their respective ageing mechanisms influenced by meteorological conditions. [ABSTRACT FROM AUTHOR]

Objective: This study evaluated the efficacy and safety of toripalimab in combination with bevacizumab and platinumbased chemotherapy as a first-line treatment for refractory recurrent or metastatic cervical cancer (R/M CC). Methods: Patients received toripalimab (240 mg, once [D1], every 3 weeks [q3W]) plus bevacizumab (7.5 mg/kg, D1, q3W) and platinum-based chemotherapy (paclitaxel 175 mg/m²+cisplatin 50 mg/m² or carboplatin area under the curve=5, D1, q3W) for 6 cycles, followed by the maintenance of toripalimab plus bevacizumab (q3W) for 12 months or until disease progression or intolerable toxicity occurred. The primary endpoint was the objective response rate (ORR) per RECIST v1.1. The secondary endpoints were safety profiles, disease control rate (DCR), progression-free survival (PFS), and overall survival (OS). Results: Twenty-four patients (range, 33-75) were enrolled. Eleven (45.8%) patients had distant metastasis, 6 (25%) had local recurrence and 7 (29.2%) had local recurrence plus distant metastasis. The median treatment duration was 10.97 (range, 0.76-12.19) months. The ORR was 83.3% (20/24; 95% confidence interval [CI]=63.6-95.3) and the DCR was 95.8% (23/25, 95% CI=78.9-99.9), including 9 patients achieved complete response, 11 patients attained partial response, and 3 patients had stable disease. The median time to respond was 1.5 (range, 1.2-9.0) months. The median duration of response was not reached. The median PFS was 22.57 (95% CI=18.4-26.74) months, and the median OS was not reached. Treatment-related adverse events (TRAEs) of any grade occurred in 22 (22/24, 91.7%) patients. Grade ≤3 TRAEs occurred in 14 (14/24, 58.3%) patients. Conclusion: Toripalimab plus bevacizumab and chemotherapy is a promising treatment approach for patients with R/M CC. [ABSTRACT FROM AUTHOR]

The physical and chemical properties of black carbon (BC) and organic aerosols are important for predicting their radiative forcing in the atmosphere. During the Soot Aerodynamic Size Selection for Optical properties (SASSO) project and a EUROCHAMP-2020 transnational access project, different types of light absorbing carbon were studied, including BC from catalytically stripped diesel exhaust, a flame burner, a colloidal graphite standard (Aquadag), and from controlled flaming wood combustion. Brown carbon (BrC) was also investigated in the form of organic aerosol emissions from wood burning (pyrolysis and smouldering) and from the nitration of secondary organic aerosol (SOA) proxies produced in a photochemical reaction chamber. Here we present insights into the physical and chemical properties of the aerosols, with optical properties being presented in subsequent publications. The dynamic shape factor (χ) of BC particles and material density (ρm) of organic aerosols were investigated by coupling a charging-free Aerodynamic Aerosol Classifier (AAC) with a Centrifugal Particle Mass Analyzer (CPMA) and Scanning Mobility Particle Sizer (SMPS). The morphology of BC particles was captured by transmission electron microscopy (TEM). For BC particles from the diesel engine and flame burner emissions, the primary spherule sizes were similar, around 20 nm. With increasing particle size, BC particles adopted more collapsed/compacted morphologies for the former source but tended to show more aggregated morphologies for the latter source. For particles emitted from the combustion of dry wood samples, the χ of BC particles and the ρm of organic aerosols were observed in the ranges 1.8-2.17 and 1.22-1.32 g/cm³, respectively. Similarly, for wet wood samples, the χ and ρm ranges were 1.2-1.85 and 1.44-1.60 g/cm³, respectively. Aerosol mass spectrometry measurements show no clear difference in mass spectra of the organic aerosols in individual burn phases (pyrolysis or smouldering phase) with the moisture content of the wood samples. This implies that the effect moisture has on the organic chemical profile of wood burning emissions is through changing the durations of the different phases of the burn cycle, not through the chemical modification of the individual phases. In this study, the incandescence signal of a Single Particle Soot Photometer (SP2) was calibrated with three different types of BC particles and compared with that from an Aquadag standard that is commonly used to calibrate SP2 incandescence to a BC mass. A correction factor is defined as the ratio of the incandescence signal from an alternative BC source to that from the Aquadag standard, and took values of 0.82 (or 0.79), 0.88 and 0.84-0.91 for the BC particles emitted from the diesel engine running under hot (or cold idle) conditions, the flame burner and wood combustion, respectively. These correction factors account for differences in instrument response to BC from different sources compared to the standardised Aquadag calibration and are more appropriate than the common value of 0.75 recommended by Laborde et al. (2012b) when deriving the mass concentration of BC emitted from diesel engines. Quantifying the correction factor for many types of BC particles found commonly in the atmosphere may enable better constraints to be placed on this factor depending on the BC source being sampled, and thus improve the accuracy of future SP2 measurements of BC mass concentrations. [ABSTRACT FROM AUTHOR]

Secondary organic aerosol (SOA) produced by atmospheric oxidation of primary emitted precursors is a major contributor to fine particulate matter (PM2.5) air pollution worldwide. Observations during winter haze pollution episodes in urban China show that most of this SOA originates from fossil-fuel combustion but the chemical mechanisms involved are unclear. Here we report field observations in a Beijing winter haze event that reveal fast aqueousphase conversion of fossil-fuel primary organic aerosol (POA) to SOA at high relative humidity. Analyses of aerosol mass spectra and elemental ratios indicate that ring-breaking oxidation of POA aromatic species, leading to functionalization as carbonyls and carboxylic acids, may serve as the dominant mechanism for this SOA formation. A POA origin for SOA could explain why SOA has been decreasing over the 2013-2018 period in response to POA emission controls even as emissions of volatile organic compounds (VOCs) have remained flat. [ABSTRACT FROM AUTHOR]

Primary organic aerosol (POA) is a major component of PM2.5 in the winter polluted air in the North China Plain (NCP), but our understanding on the atmospheric aging process of POA particles and the resulting influences on their optical properties is limited. As part of the Atmospheric Pollution and Human Health in a Chinese Megacity (APHH-Beijing) programme, we collected airborne particles at an urban site (Beijing) and an upwind rural site (Gucheng, Hebei province) in the NCP during 13-27 November 2016 for microscopic analyses. We confirmed that a distinct group of spherical or irregular POA particles with high viscosity, defined as primary organic tar (POT) particles, was emitted from the domestic coal and biomass burning at the rural site and was further transported to the urban site during the regional wintertime hazes. During the heavily polluted period (PM2.5 > 200 μg m-3), more than 60% of the POT particles were thickly coated with secondary inorganic aerosols (named as core-shell POT-SIA particle) through the aging process, suggesting that POT particles can provide surfaces for the heterogeneous reactions of SO2 and NOx. As a result, their average particle-to-core ratios at the rural and urban sites in the heavily polluted period increased to 1.60 and 1.67, respectively. Interestingly, we found that the aging process did not change the morphology and sizes of the POT cores, indicating that POT particles are quite inert in the atmosphere and can be transported long distances. We using the Mie theory estimated that the light absorption of individual POT particles was enhanced by ~1.39 times in the heavily polluted period at the rural and urban sites due to the lensing effect of secondary inorganic coatings. We highlight that the lensing effect on POT particles should be considered in radiative forcing models and the governments should 36 continue to promote clean energy in rural areas to effectively reduce primary emissions. [ABSTRACT FROM AUTHOR]

Black carbon (BC) forms an important component of particulate matter globally, due to its impact on climate, the environment, and human health. Identifying and quantifying its emission sources is critical for effective policymaking and achieving the desired reduction in air pollution. In this study, we present the first direct measurements of urban BC fluxes using eddy-covariance. The measurements were made over Beijing within the UK-China Air Pollution and Human Health (APHH) winter 2016 and summer 2017 campaigns. In both seasons, the mean measured BC mass (winter: 5.49 ng m-2 s-1, summer: 6.10 ng m-2 s-1) and number fluxes (winter: 261.25 particles cm-2 s-1, summer: 334.37 particles cm-2 s-1) were similar. Traffic was determined to be the dominant source of the BC fluxes measured during both seasons. The total BC emissions within the 2013 Multi-resolution Emission Inventory for China (MEIC) are on average too high compared to measured fluxes by a factor of 58.8 (winter) and 47.2 (summer). Comparison of MEIC transport sector only are also larger (factor winter: 37.5, summer: 37.7) than the measured flux. Emission ratios of BC/NOx and BC/CO are comparable to vehicular emission control standards implemented in January 2017 for gasoline (China 5) and diesel (China V) engines, indicating reduction of BC emissions within central Beijing and extending this to a larger area would further reduce total BC concentrations. [ABSTRACT FROM AUTHOR]

As one of the intense anthropogenic emission regions across the relatively high latitude (> 40° N) areas on the Earth, Northeast China faces serious problem on regional haze during long winter with half a year. Aerosols in polluted haze in Northeast China are poorly understood compared with the haze in other regions of China such as North China Plain. Here, we for the first time integrated bulk chemical measurements with single particle analysis from transmission electron microscopy (TEM), nanoscale secondary ion mass spectrometer (NanoSIMS), and atomic force microscopy (AFM) to obtain morphology, size, composition, aging process, and sources of aerosol particles collected during two contrasting regional haze events (Haze-I and Haze-II) at an urban site and a mountain site in Northeast China, and further investigated the causes of regional haze formation. Haze-I evolved from moderate (average PM2.5: 76-108 μg/m³) to heavy pollution (151-154 μg/m³), with the dominant PM2.5 component changing from organic matter (OM) (39-45 μg/m³) to secondary inorganic ions (94-101 μg/m³). Similarly, TEM observations showed that S-OM particles elevated from 29 % to 60 % by number at urban site and 64 % to 74 % at mountain site and 75-96 % of Haze-I particles included primary OM. Change of wind direction induced that Haze-I rapidly turned into Haze-II (185-223 μg/m³) with the predominant OM (98-133 μg/m³) and unexpectedly high K+ (3.8 μg/m³). TEM also showed that K-OM particles increased from 4-5 % by number to 50-52 %. Our study revealed a contrasting formation mechanism of these two haze events: Haze-I was induced by accumulation of primary OM emitted from residential coal burning and further deteriorated by secondary aerosol formation via heterogeneous reactions; Haze-II was caused by long-range transport of agricultural biomass burning emissions. Moreover, we found that 75-97 % of haze particles contained tarballs, but only 4-23 % contained black carbon and its concentrations were low at 2.7-4.3 μg/m³. The results highlight that abundant tarballs are important light-absorbing brown carbon in Northeast China during winter haze and further considered in climate models. [ABSTRACT FROM AUTHOR]

The water-uptake on aerosol influences its optical depth and capacity of cloud formation, depending on the vertical profile of aerosol hygroscopicity because of different solar radiation received and supersaturation conditions at different atmospheric levels. Such information is lack over the polluted eastern Asian region. This study presents aircraft in-situ measured aerosol size distribution and chemical compositions by series of flights over Beijing area in wintertime. Under high relative humidity conditions (surface RH > 60 %, hRH), a significant enhancement of aerosol hygroscopicity parameter (κ) in the planetary boundary layer (PBL) was observed to increase by 50 % up to 0.32 from the surface to the top of PBL (vertical gradient of ~0.13 km−1), along with the dry particle effective diameter (Deff) increased by 71 % and activation ratio up to 0.23 (0.64) at SS = 0.05 % (0.1 %), in contrast with a lower vertical gradient of κ (0.05 km−1) and smaller Deff under low RH conditions (surface RH < 60 %, lRH). This suggests the aqueous processes played an important role on promoting the enhancement of particle hygroscopicity in the PBL. The κ in the lower free troposphere (LFT) was relatively stable at 0.24 ± 0.03 with slight increase during regional transport. The enhancement of aerosol optical depth (AOD) due to water uptake ranged at 1.0–1.22 for PBL under lRH and LFT, but reached as high as 6.4 in the PBL under hRH. About 80 % and 18 % of the AOD was contributed by aerosol hygroscopic growth under hRH and lRH respectively. These results emphasize the importance of boundary layer processing on aerosol water-uptake capacity especially under high RH condition. [ABSTRACT FROM AUTHOR]

The effect of observational constraint on the ranges of uncertain physical and chemical process parameters was explored in a global aerosol-climate model. The study uses 1 million variants of the HadGEM3-UKCA climate model that sample 26 sources of uncertainty, together with over 9000 monthly aggregated grid-box measurements of aerosol optical depth, PM2.5, particle number concentrations, sulphate and organic mass concentrations. Despite many compensating effects in the model, the procedure constrains the probability distributions of parameters related to secondary organic aerosol, anthropogenic SO2 emissions, residential emissions, sea spray emissions, dry deposition rates of SO2 and aerosols, new particle formation, cloud droplet pH and the diameter of primary combustion particles. Observational constraint rules out nearly 98 % of the model variants. On constraint, the ± 1σ (standard deviation) range of global annual mean direct radiative forcing, RFari, is reduced by 33 % to -0.14 to -0.26 W m-2, and the 95 % credible interval (CI) is reduced by 34 % to -0.1 to -0.32 W m-2. For the global annual mean aerosol-cloud radiative forcing, RFaci, the ± 1σ range is reduced by 7 % to -1.66 to -2.48 W m-2, and the 95 % CI by 6 % to -1.28 to -2.88 W m-2. The tightness of the constraint is limited by parameter cancellation effects (model equifinality) as well as the large and poorly defined representativeness error associated with comparing point measurements with a global model. The constraint could also be narrowed if model structural errors that prevent simultaneous agreement with different measurement types in multiple locations and seasons could be improved. For example, constraints using either sulphate or PM2.5 measurements individually result in RFari ± 1σ ranges that only just overlap, which shows that emergent constraints based on one measurement type may be over-confident. [ABSTRACT FROM AUTHOR]

Characterizing vertical profiles of aerosol optical properties is important because only replying on the surface or column-integrated measurements is unable to unambiguously constrain the radiative impacts of aerosol. This study presents series of vertical profiles of in-situ measured multi-wavelength optical properties of aerosols during three pollution events in Nov. to Dec. 2016 over Beijing region. For all pollution events, clean periods (CP) before pollution initialization showed higher scattering Ångström exponent and smaller asymmetry parameter (g), and relatively uniform vertical structures. The heavy pollution (HP) periods showed increased particle size, causing these parameters to vary in the opposite way. During the transition periods (TP), regional transport of aged aerosols at upper level was found. The AERONET aerosol optical depth (AOD) matched the in-situ measurements within 10 %, however the AERONET absorption optical depth (AAOD) was 10–20 % higher than in-situ measurements, and this positive discrepancy increased to 30 % at shorter wavelength. The absorption of brown carbon (BrC) was identified by increased absorption Ångström exponent (AAE), and the heating rate of black carbon (BC) and BrC was calculated by computing the wavelength-dependent absorption coefficient and actinic flux by the radiative transfer model. BC and BrC had heating rate up to 0.18 K/h and 0.05 K/h in the planetary boundary layer (PBL) respectively during the pollution period. The fraction of BrC absorption increased from 12 % to 40 % in the PBL from CP to HP period. Notably, higher contribution of BrC heating was found above the PBL under polluted condition. This study gives a full picture of shortwave heating impacts of carbonaceous aerosols during different stages of pollution event, and highlights the increased contribution of BrC absorption especially at higher level during pollution. [ABSTRACT FROM AUTHOR]

Biological aerosols play an important role in atmospheric chemistry, clouds, climate, and public health. Here, we studied the morphology and composition of primary biological aerosol particles (PBAPs) collected in the Lesser Khingan Mountain boreal forest of China in summertime using transmission electron microscopy and scanning electron microscopy. Of all detected particles > 100 nm in diameter, 13 % by number were identified as PBAPs. In addition, 57 % of the PBAPs were identified as bacteria, followed by brochosomes (24 %) and fungi (19 %). The dominant size of bacteria was 1–4 μm, fungi was 2–4 μm, and brochosomes was 300–500 nm. The number size distribution of PBAPs coupled with the mass concentrations of PM2.5 and PM10 were used to estimate the total mass concentration of PBAPs, which is approximately 1.9 μg m−3 and accounts for 47 % of the in situ PM2.5–10 mass. C, N, O, P, K, and Si are detected in all PBAP particles, and P represented a major marker to identify PBAPs. Moreover, there is a higher frequency and concentration of PBAPs at night compared with day. Bacterial and fungal particles displayed weak hygroscopicity with a growth factor of ~ 1.09 at RH = 94 %. Electron microscopy shows that approximately 20 % of the bacterial particles were internally mixed with metal, mineral dust, and inorganic salts in the boreal forest air. This work provides a database for both further understanding physicochemical state of individual PBAP particles from natural sources and expanding the scope of atmospheric implications. [ABSTRACT FROM AUTHOR]

Black carbon (BC) is known to have major impacts on both climate and human health, so is therefore of global importance, particularly so in regions close to large populations that have strong sources. The physical properties and mixing state of black carbon containing particles are important determinants in these effects but information is often lacking, particularly in some of the most important regions of the globe. Detailed analysis into the vertical and horizontal BC optical and physical properties across northern India has been carried out using airborne in-situ measurements. The size-resolved mixing state of BC-containing particles was characterised using a single particle soot photometer (SP2). The study focusses on the Indo-Gangetic Plain during the pre-monsoon and monsoon seasons. Data presented are from the UK Facility for Airborne Atmospheric Measurements BAe-146 research aircraft that performed flights during the pre-monsoon (11th and 12th June) and monsoon (30th June to 11th July) seasons of 2016. Over the Indo-Gangetic Plain, BC mass concentrations were greater (1.95 µg/m3) compared to north-west India (1.50 µg/m3) and north-east India (0.70 µg/m3) during the pre-monsoon. Across northern India, two distinct BC modes were recorded; a mode of small BC particles (core diameter < 0.16 µm and coating thickness < 50 nm) and a mode of moderately-coated BC (core diameter < 0.22 µm and coating thickness 50–200 nm). The Indo-Gangetic Plain and north-east India locations exhibited moderately-coated black carbon particles with enhanced coating thicknesses, core sizes, mass absorption cross sections and scattering enhancement values compared to much lower values present in the north-west. The coating thickness and mass absorption cross section increased with altitude (13 %) compared to the boundary layer. As the monsoon arrived across the region, mass concentration of BC decreased over the central Indo-Gangetic Plain and north-east locations (38 % and 28 % respectively), except for the north-west location where BC properties remained relatively consistent. Post-monsoon onset, the coating thickness, core size, mass absorption cross section and scattering enhancement values were all greatest over the central Indo-Gangetic Plain much like the pre-monsoon but were considerably reduced over both north-east and north-west India. Increases in mass absorption cross section through the atmospheric column were still present during the monsoon for the north-west and central Indo-Gangetic Plain locations, but less so over the north-east due to lack of long-range transport aerosol aloft. Across the Indo-Gangetic Plain and north-east India during the pre-monsoon and monsoon, solid fuel (wood burning) emissions form the greatest proportion of BC with moderately-coated particles. However, as the monsoon develops in the north-east there was a switch to small uncoated BC particles indicative of traffic emissions, but the solid fuel emissions remained in the IGP into the monsoon. For both seasons in the north-west, traffic emissions form the greatest proportion of BC particles. Our findings will prove important for greater understanding of the BC physical and optical properties, with important consequences on the atmospheric radiative forcing of BC-containing particles. It will also be useful for BC source and emission inventory studies in the future. [ABSTRACT FROM AUTHOR]

Refractory Black Carbon (rBC) in the atmosphere is known for its significant impact on the climate system in the atmosphere. The relationship between the microphysical and optical properties of rBC remain uncertain and are largely influenced by the size, coating thickness and mixing state of particles. This study presents a coupling of a centrifugal particle mass analyser (CPMA) and a single particle soot photometer (SP2) for the morphology-independent quantification of the mixing state of rBC-containing particles, used in the urban site of Beijing as part of the Air Pollution and Human Health-Beijing (APHH-Beijing) project during winter (10th Nov–10th Dec) and summer (18th May–25th June). An inversion method is applied to the measurements to present a two-variable distribution of both rBC core mass and total mass of rBC-containing particles and present the mass-resolved mixing state of rBC-containing particles. The mass ratio between non-rBC coating and rBC core (MR) is calculated to determine the coating thickness of the rBC-containing particles. The bulk MR was found to vary between 2–12 in winter and between 2–3 in summer. This mass-resolved mixing state is used to derive the mixing state index (χ) for the rBC-containing particles. χ quantifies whether the coating is evenly distributed across the rBC-containing particle population and is used to determine the degree of internal and external mixture of rBC-containing particles. The rBC-containing particles in Beijing were found to be 55%–70 % internally mixed in winter depending on the dominant air masses. χ of rBC-containing particles was highly positively associated with increased bulk MR, rBC mass loading or pollution level in winter, whereas χ of rBC-containing particles in summer varied significantly (ranging 60 %–75 %) within the narrowly-distributed bulk MR and was found to be independent of air mass sources. This concludes that the bulk MR may only act as a predictor of mixing state in winter, and χ is better to quantify the mixing state of rBC-containing particles. The same level of bulk MR corresponded with a higher χ in summer than in winter and this tended to suggest a limited formation of coatings on rBC largely depended on primary sources. However, with the higher Non-refractory PM1 (NR-PM1) concentration in winter, the coagulation process may still lead relative thick coatings. In summer the higher secondary compounds made the rBC-containing particles more homogeneous. But due to the higher temperatures and limited pollution level, the coating thickness in summer is limited. The mixing state of rBC-containing particles should also depend on the coating formation mechanism, both primary source influence and secondary coating formation mechanism should be considered in interpreting the rBC-containing particles mixing state in the atmosphere. This particle morphology-independent and mass-based data format as introduced in this study could be conviently applied in particle-resolved or other process models to investigate atmospheric rBC aging and mixing state properties. [ABSTRACT FROM AUTHOR]

Over the Indian region, aerosol absorption is considered to have potential impact on regional climate, monsoon and hydrological cycle. Black carbon (BC) is the dominant absorbing aerosol, whose absorption potential is largely determined by its microphysical properties, including its concentration, size and mixing state with other aerosol components. The Indo-Gangetic Plains (IGP) is one of the regional aerosol hot spots with diverse sources, both natural and anthropogenic, but still the information on the mixing state of the IGP aerosols, especially BC, is limited and a major source of uncertainty in understanding their climatic implications. In this context, we present the results from intensive measurements of refractory BC (rBC) carried out over Bhubaneswar, an urban site in the eastern coast of India, which experiences contrasting airmasses (the IGP outflow or coastal/marine airmasses) in different seasons. This study helps to elucidate the microphysical characteristics of BC over this region and delineates the IGP outflow from the other airmasses. The observations were carried out as part of South West Asian Aerosol Monsoon Interactions (SWAAMI) collaborative field experiment during July 2016-May 2017, using a single particle soot photometer (SP2) that uses a laser-induced incandescence technique to measure the mass and mixing state of individual BC particles and an aerosol chemical speciation monitor (ACSM). Results highlighted the distinctiveness in aerosol microphysical properties in the IGP airmasses. BC mass concentration was highest during winter (~1935 ± 1578ngm-3), when the prevailing air masses were mostly of IGP origin, followed by post-monsoon (mean ~1338 ± 1396ngm-3). Mass median diameter (MMD) of the BC mass size distributions were in the range 0.190-0.195µm suggesting mixed sources of BC, and further, higher values (~1.3-1.8) of bulk relative coating thickness (RCT) (ratio of optical and core diameters) were seen indicating a large fraction of highly coated BC aerosols in the IGP outflow. During the pre-monsoon, when marine/coastal airmasses prevailed, BC mass concentration was lowest (~816 ± 835ngm-3) and larger BC cores (MMD > 0.210µm) were seen suggesting distinct source processes, while RCT was ~1.2-1.3, which may translate into higher extent of absolute coating on BC cores which may have important regional climate implications. During the summer monsoon, BC size distributions were dominated by smaller cores (MMD ≤ 0.185µm) with lowest coating, indicating fresher BC, likely from fossil fuel sources. A clear diurnal variation pattern of BC and RCT was noticed in all the seasons, and day time peak in RCT suggested enhanced coating on BC due to the condensable coating material originated from photochemistry. Examination of sub-micron aerosol chemical composition highlighted that the IGP outflow is dominated by organics (47-49%) and marine/coastal airmasses contained greater amounts of sulphate (41-47%), while ammonium and nitrate were seen in minor amounts with significant concentrations only during the IGP airmass periods. The diurnal pattern of sulphate resembled that of the RCT of rBC particles, whereas organic mass showed a pattern similar to that of the rBC mass concentration. Though the pre-monsoon is sulphate dominated, the coating on BC showed a negative association with sulphate and same is true for organic mass during the post-monsoon, suggesting preferential coating and importance of source processes (and co-emitted species) on the mixing state of BC. This is the first experimental data on the mixing state of BC from a long time series over the Indian region, and includes new information on black carbon in the IGP outflow region. This data helps in improving the understanding of regional BC microphysical characteristics and their climate implications. [ABSTRACT FROM AUTHOR]

Black carbon aerosols play an important role in climate change by absorbing solar radiation and degrading visibility. In this study, the mixing state of refractory black carbon (rBC) at an urban site in Beijing was studied with a single particle soot photometer (SP2), as well as a tandem observation system with a centrifugal particle mass analyzer (CPMA) and a differential mobility analyzer (DMA), in early summer of 2018. The results demonstrated that the mass-equivalent size distribution of rBC exhibited an approximately lognormal distribution with a mass median diameter (MMD) of 171.2nm. When the site experienced prevailing southerly winds, the MMD of rBC increased notably by 19%. During the observational period, the ratio of the diameter of rBC-containing particles (Dp) to the rBC core (Dc) was 1.20 on average for Dc=180nm, indicating that the majority of rBC particles were thinly coated. The Dp/Dc value exhibited a clear diurnal pattern, with a maximum at 1400LST and an enhancing rate of 0.013/h; higher Ox conditions increased the coating enhancing rate. Bare rBC particles were primarily in a fractal structure with a mass fractal dimension (Dfm) of 2.35, with limited variation during both clean and pollution periods, indicating significant impacts from on-road vehicle emissions. The morphology of rBC-containing particles vairied with aging processes. The mixing state of rBC particles could be indicated by the mass ratio of non-refractory matter to rBC (MR). In the present study, rBC-containing particles were primarily found in an external fractal structure when MR<1.5 and changed to a core-shell structure when MR>6, at which the measured scattering cross section of rBC-containing particles was consistent with that based on the Mie-scattering simulation. We found only 9% of the rBC-containing particles were in core-shell structures on clean days with a particle mass of 10fg, and the number fraction of core-shell structures increased considerably to 32% on pollution days. Considering the morphology change, the absorption enhancement (Eabs) was 11.7% higher based on core-shell structures. This study highlights the combined effects of morphology and coating thickness on the Eabs of rBC-containing particles, which will be helpful for determining the climatic effects of BC. [ABSTRACT FROM AUTHOR]

We present a range of airborne in-situ observations of biomass burning carbonaceous aerosol over tropical South America, including a case study of a large tropical forest wildfire and a series of regional survey flights across the Brazilian Amazon and Cerrado. The study forms part of the South American Biomass Burning Analysis (SAMBBA) Project, which was conducted during September and October 2012. We find limited evidence for net increases in aerosol mass through atmospheric aging combined with substantial changes in the chemical properties of organic aerosol (OA). Oxidation of the OA increases significantly and rapidly on the scale of 2.5–3 hours based on our case study analysis and is consistent with secondary organic aerosol production. The observations of limited net enhancement in OA coupled with such changes in chemical composition, imply that evaporation of OA is also occurring to balance these changes. We observe significant coatings on black carbon particles at source, but with limited changes with aging in both particle core size and coating thickness. We quantify variability in the ratio of OA to carbon monoxide across our study as a key parameter representing both initial fire conditions and an indicator of net aerosol production with atmospheric aging. We observe ratios of 0.075–0.13 μg sm−3 ppbv−1 in the west of our study region over the Amazon tropical forest in air masses less influenced by precipitation and a value of 0.095 μg sm−3 ppbv−1 over the Cerrado environment in the east. Such values are consistent with emission factors used by numerical models to represent biomass burning OA emissions. Black carbon particle core sizes typically range from 250–290 nm, while coating thicknesses range from 40–110 nm in air masses less influenced by precipitation. The primary driver of the variability we observe appears to be related to changes at the initial fire source. A key lesson from our study is that the complex nature of the regional aerosol and its drivers precludes aggregating our observations as a function of atmospheric aging due to the many conflating and competing factors present. Our study explores and quantifies key uncertainties in the evolution of biomass burning aerosol at both nearfield and regional scales. Our results suggest that the initial conditions of the fire are the primary driver of carbonaceous aerosol physical and chemical properties over tropical South America, aside from significant oxidation of OA during atmospheric aging. Such findings imply that uncertainties in the magnitude of the aerosol burden and its impact on weather, climate, health and natural ecosystems most likely lie in quantifying emission sources, alongside atmospheric dispersion, transport and removal rather than chemical enhancements in mass. [ABSTRACT FROM AUTHOR]

Despite ongoing efforts, the vertical distribution of aerosols globally is poorly understood. This in turn leads to large uncertainties in the contributions of the direct and indirect aerosol forcing on climate. Using the Global Aerosol Synthesis and Science Project (GASSP) database – the largest synthesised collection of in-situ aircraft measurements currently available, with more than 1000 flights from 37 campaigns from around the world – we investigate the vertical structure of sub-micron aerosols across a wide range of regions and environments. The application of this unique dataset to assess the vertical distributions of number size distribution and Cloud Condensation Nuclei (CCN) in the global aerosol-climate model ECHAM-HAM reveals that the model underestimates accumulation mode particles in the upper troposphere, especially in remote regions. The processes underlying this discrepancy are explored using different aerosol microphysical schemes and a process sensitivity analysis. These show that the biases are predominantly related to aerosol ageing and removal rather than emissions. [ABSTRACT FROM AUTHOR]

Rapid economic growth in China over the past 30 years has resulted in significant increases in the concentrations of small particulates (PM2.5) over the city of Beijing. In addition to health problems, high aerosol loading can impact visibility and thus reduce photolysis rates over the city leading to potential implications for photochemistry. Photolysis rates are highly sensitive not only to the vertical distribution of aerosols but also to their composition as this can impact how the incoming solar radiation is scattered or absorbed. This study, for the first time, uses aerosol composition measurements and lidar optical depth to drive the Fast-JX photolysis scheme and quantify the photochemical impacts of different aerosol species during the Air Pollution and Human Health (APHH) measurement campaigns in Beijing in November-December 2016 and May-June 2017. This work demonstrates that severe haze pollution events (PM2.5 > 75μgm-3) occur during both winter and summer leading to reductions in O3 photolysis rates of 27.4-34.0% (greatest in winter) and reductions in NO2 photolysis of 40.4-66.2% (greatest in summer) at the surface. It also shows that in spite of much lower PM2.5 concentrations in the summer months, the absolute changes in photolysis rates are larger for both O3 and NO2. In the winter, absorbing species such as black carbon dominate the photolysis response to aerosols leading to mean reductions in J[O1D] and J[NO2] in the lowest 1km of 23.8% and 23.1% respectively. In contrast in the summer, scattering aerosol such as organic matter dominate the response leading to mean decreases of 2.0-3.0% at the surface and increases of 8.4-10.1% at higher altitudes (3-4km). During these haze events in both campaigns, the influence of aerosol on photolysis rates dominates over that from clouds. These large impacts on photochemistry can have important implications for concentrations of important atmospheric oxidants such as the hydroxyl radical. [ABSTRACT FROM AUTHOR]

Black carbon (BC) is known to have major impacts on both human health and climate. The populated megacity represents the most complex anthropogenic BC emissions where the sources and related impacts are very uncertain. This study provides source attribution and characterization of BC in the Beijing urban environment during the joint UK-China APHH (Air Pollution and Human Health) project, in both winter (Nov.–Dec. 2016) and summer (May–Jun. 2017). The size-resolved mixing state of BC-containing particles was characterized by a single particle soot photometer (SP2) and their mass spectra was measured by a soot particle mass spectrometer (SP-AMS). The refractory BC (rBC) mass loading was around a factor of 2 higher in winter relative to summer and more variable coatings were present, likely as a result of additional surface emissions from the residential sector and favourable condensation in cold season. The characteristics of the BC were relatively independent of air mass direction in summer; whereas in winter the airmass from the Northern Plateau had a significant dilution effect resulting in less-coated and smaller BC, whereas the BC from the Southern Plateau had the largest core size and coatings. We combine two online source apportionment methods for the first time, by the physical method from the SP2, and the chemical approach using the positive matrix factorization (PMF) of mass spectra from the SP-AMS. A method is proposed to isolate the BC from the transportation sector using a mode of small BC particles (core diameter Dc<0.18μm and coating thickness ct<50nm). This mode of BC highly correlated with NOx concentration in both seasons (~14ngm−3BCppb−1NOx) and corresponded with the morning traffic rush hour, contributing about 30% and 40% of the total rBC mass (35% and 55% in number) in winter and summer respectively. The BC from coal burning or biomass burning tended to dominate with moderate coatings (ct=50–200nm) contributing ~20–25% of rBC mass. Large uncoated BC particles (Dc>0.18μm and ct<50nm) was more likely to be contributed by coal combustion, as these particles were not present in urban London. This mode was present in Beijing in both winter (~30–40% rBC mass) and summer (~40% rBC mass) but may be dominated by residential and industrial sector respectively. The contribution of BC thickly-coated with secondary species (ct>200nm) to the total rBC mass increased with pollution level in winter, but was minor in summer. These large BC importantly enhanced the absorption efficiency at high pollution levels – in winter when PM1>100μgm−3 or BC>2μgm−3, the absorption efficiency of BC increased by 25–70%. Reduction of emissions of these large BC particles and the precursors of the associated secondary coating will be an effective way of mitigating the heating effect of BC in urban environments. [ABSTRACT FROM AUTHOR]

Black carbon (BC), from the incomplete combustion sources (mainly fossil fuel, biofuel and open biomass burning), is chemically inertness and optical absorbance in the atmosphere. It has significant impacts on global climate, regional air quality, and human health. During the transportation, its physical-chemical characteristics, optical properties and sources would change dramatically. To investigate the BC properties (i.e., mass concentration, sources and optical properties) during the intra-regional transport between the south edge of North China Plain (SE-NCP) and Central China (CC), simultaneous observations of BC at a megacity (Wuhan, WH) in CC, three borderline cities (Xiangyang, XY, Suixian, SX and Hong'an, HA, distributing from the west to east) between SE-NCP and CC and a city (Luohe, LH) in SE-NCP were conducted during the typical winter haze episodes. Using Aethalometer, the highest equivalent BC (eBC) mass concentrations and aerosol absorption coefficients (σabs) were found in the city (LH) at SE-NCP, followed by the borderline cities (XY, SX and HA) and megacity (WH). The levels, sources, optical properties (i.e., σabs and absorption Ångström exponent, AAE) and geographic origins of eBC were different between clean and pollution episodes. Compared to clean days, the higher eBC levels (increased by 26.4-163 %) and σabs (increased by 18.2-236 %) were found during pollution episodes due to more combustion of fossil fuel (contributing for 51.1-277 %), supported by the decreased AAE (by 7.40-12.7 %). Non-parametric wind regression (NWR) and concentration-weighted trajectory (CWT) results showed that the geographic origins of biomass burning (BCbb) and fossil fuel (BCff) combustion derived BC were different. Based on cluster analysis of trajectories, air parcels from south direction dominated for border sites during clean days, with contributions of 46.0-58.2 %, while trajectories from the northeast had higher contributions (37.5-51.2 %) during pollution episodes. At the SE-NCP site (LH), transboundary influences from south direction (CC) exhibited more frequent impact (with the air parcels from this direction contributed 47.8 % of all the parcels) on the ambient eBC levels during pollution episodes. At WH, eBC was mainly from the northeast transport route during the whole observation period. Two transportation cases showed that from upwind to downwind direction, the mass concentrations of eBC, BCbb and BCff all increased, while AAE decreased. This study highlighted that intra-regional prevention and control for dominated sources of specific sites should be considered to improve the regional air quality. [ABSTRACT FROM AUTHOR]

Refractory black carbon (BC) is a product from incomplete combustion of fossil fuel, biomass and biofuel, etc. By mixing with other species, BC can play significant roles in climate change, visibility impairment and human health. Such BC-containing particles in very densely-populated megacities, like Beijing, may have specific sources and properties, that are very important to the haze formation and air quality. In this work, we characterized exclusively the BC-containing particles only in urban Beijing, by using a laser-only Aerodyne soot particle aerosol mass spectrometer (SP-AMS), as a part of the Air Pollution and Human Health (APHH) 2016 winter campaign. The average mass ratio of coating-to-BC (RBC) was found to be ~ 5.0, much smaller than those of highly aged BC, indicating dominant contributions from primary emissions. Positive matrix factorization indeed shows the dominance of fossil fuel and biomass burning organics. Yet secondary species, including both sulfate, nitrate and oxygenated organic aerosol (OA) species, could have significant impacts on the properties of BC-containing particles, especially for ones with larger BC core sizes and thicker coatings. Analyses of the sources and diurnal cycles of organic coating reveal significant afternoon photochemical production of secondary OA (SOA), as well as the nighttime production of a portion of highly oxygenated OA. Besides SOA, photochemical production of nitrate, not sulfate, was very important. Further investigations on BC-containing particles at different periods show that, on average, more polluted periods would have more contributions from secondary species, and more thickly coated BC tended to associate with more secondary species, indicating the important role of chemical aging to the air pollution in urban Beijing during wintertime. However, for individual pollution events, aqueous-phase production of sulfate, nitrate and SOA might aggravate the pollution obviously under high relative humidity conditions, while sometimes local primary emissions (coal and biomass burning) could lead to serious and extremely polluted event too. [ABSTRACT FROM AUTHOR]

Aerosol particles are of importance in the Earth's radiation budget since they scatter and absorb sunlight. While extensive studies of aerosol optical properties have been conducted at ground sites, vertical measurements and characterization are very limited in megacities. In this work, we present simultaneous real-time online measurements of aerosol optical properties at ground level and at 260 m on a meteorological tower from 16 November to 13 December in 2016 in Beijing along with measurements of continuous vertical profiles during two haze episodes. The average (± 1σ) scattering and absorption coefficients (bsca and babs, λ = 630 nm) were 337.6 (± 356.0) and 36.6 (± 33.9) Mm-1 at 260 m, which were 26.5% and 22.5% lower than those at ground level. Single scattering albedo (SSA), however, was comparable between the two heights with slightly higher values at ground level (0.89 ± 0.04). Although bsca and babs showed overall similar temporal variations between ground and 260 m, the ratios of 260 m to ground varied substantially from less than 0.4 during the cleanest stages of haze episodes to > 0.8 in the late afternoon. A more detailed analysis indicates that vertical profiles of bsca, babs, and SSA in the low atmosphere were closely related to the changes in meteorological conditions and mixing layer height. The mass absorption cross-section MAC of BC (λ = 630 nm) varied substantially from 9.5 to 13.2 m² g-1 in winter in Beijing, and it was strongly associated with the mass ratio of non-refractory BC (rBC) materials to rBC (MR), and also the oxidation degree of organics in rBC-containing particles. Our results show that the increases in MAC of BC in winter were mainly caused by photochemically produced secondary materials. Light absorption of organic carbon (brown carbon, BrC) was also important in winter, which on average accounted for 46 (± 8.5) % and 48 (± 9.3) % of the total absorption at 370 nm at ground level and 260 m, respectively. A Linear regression model combined with positive matrix factorization analysis was used to show that coal combustion was the dominant source contribution of BrC (48-55%) followed by biomass burning (17%) and photochemically processed secondary organic aerosol (∼ 20%) in winter in Beijing. [ABSTRACT FROM AUTHOR]

Mineral dust is an important component of the climate system, affecting the radiation balance, cloud properties, biogeochemical cycles, regional circulation and precipitation, as well as having negative effects on aviation, solar energy generation and human health. Dust size and composition has an impact on all these processes. However, changes in dust size distribution and composition during transport, particularly for coarse particles, are poorly understood and poorly represented in climate models. Here we present new in-situ airborne observations of dust in the Saharan Air Layer (SAL) and the Marine Boundary Layer (MBL) during the beginning of its trans-Atlantic transport pathway, from the AER-D fieldwork in August 2015, within the peak season of North African dust export. This study focuses on coarse mode dust properties, including size distribution, mass loading, shape, composition, refractive indices and optical properties. Size distributions from 0.1 to 100 μm diameter (d) are presented, fully incorporating the coarse and giant modes of dust. Within the SAL, particles larger than 20 μm diameter were always present up to 5 km altitude, in concentrations over 10-5 cm-3, constituting up to 40% of dust mass. Mean effective diameter and volume median diameter were 4.0 μm and 5.5 μm respectively. Larger particles were detected in the SAL than can be explained by sedimentation theory alone. Coarse mode composition was dominated by quartz and alumino-silicates; the accumulation mode showed a strong contribution from sulfate-rich and sea salt particles. In the SAL, measured single scattering albedos (SSAs) at 550 nm representing d<2.5 μm were 0.93 to 0.98 (mean 0.97). Optical properties calculated for the full size distribution (0.1-1 (mean 0.32 m² g-1). Variability in SSA was mainly controlled by variability in dust composition (principally iron), rather than by variations in the size distribution, in contrast to previous observations over the Sahara where size is the dominant influence. It is important that models are able to capture this complex evolution of both dust composition and size distribution with transport in order to accurately represent the impacts of dust on climate. These results provide a new SAL dust dataset, fully representing coarse and giant particles, to aid model validation and development. [ABSTRACT FROM AUTHOR]

The mineralogy and mixing state of dust particles originating from the African continent influences climate and marine ecosystems in the North Atlantic due to its effect on radiation, cloud properties and biogeochemical cycling. Single-particle mineralogy and mixing state is particularly important in many processes but is difficult to predict because of large temporal and spatial variability and the lack of in-situ measurements of dust properties during emission, transport and deposition. This lack of measurements is in part due to the remoteness of potential source areas (PSA) and transport pathways, but also because of the lack of an efficient method to report the mineralogy and mixing state of single particles with a time resolution comparable to atmospheric processes. In this work, the mineralogy and mixing state of the fine fraction (< 2.5 μm) in laboratory suspended dust from the Sahara and Sahel were made using novel techniques with on-line single-particle mass spectrometry (SPMS) and traditional off-line scanning electron microscopy (SEM). A regional difference in mineralogy was detected, with material sourced from Morocco contained a high number fraction of illite like particles in contrast to Sahelian material which contains potassium and sodium depleted clay minerals like kaolinite. Applying the same methods to ambient measurement of transported dust in the marine boundary layer at Cabo Verde in the remote North Atlantic enabled the number fractions of illite/smectite clay mineral (ISCM), non-ISCM, and calcium containing particles to be reported at a 1 hour time resolution over a 20 day period alongside internal mixing with nitrate, sulphate and organic/biological material. The ISCM and nitrate content was found to change significantly between distinct dust events, indicating a shift in source and transport pathways which may not be captured in off-line composition analysis or remote sensing techniques. The results show SPMS and SEM techniques are complimentary and demonstrate that SPMS can provide a meaningful high resolution measurement of single-particle mineralogy and mixing state in laboratory and ambient conditions. In most cases, the mineralogy varies continuously between particles rather than a collection of discrete mineral phases. These techniques will be useful in resolving the complexity of mineral dust transport and in obtaining atmospherically relevant test material for laboratory experiments of dust properties. [ABSTRACT FROM AUTHOR]

The representation of volatile organic compound (VOC) deposition and oxidation mechanisms in the context of secondary organic aerosol (SOA) formation are developed in the United Kingdom Chemistry and Aerosol (UKCA) chemistry-climate model. Impacts of these developments on both the global SOA budget and model agreement with observations is quantified. Firstly, global model simulations were performed with varying VOC dry deposition and wet deposition. Including VOC dry deposition reduces the global annual-total SOA production rate by 2-32 %, with the range reflecting uncertainties in surface resistances. Including VOC wet deposition reduces the global annual-total SOA production rate by 15 % and is relatively insensitive to changes in effective Henry's Law coefficients. With precursor deposition, simulated SOA concentrations are lower than observed, with a normalised mean bias (NMB) of -51 %. Hence, including SOA precursor deposition worsens model agreement with observations even further (NMB = -66 %). Secondly, for the anthropogenic and biomass burning VOC precursors of SOA (VOCANT/BB), model simulations were performed varying: a) the parent hydrocarbon reactivity, b) the number of reaction intermediates, and c) accounting for differences in volatility between oxidation products from various pathways. These changes were compared to a scheme where VOCANT/BB adopts the reactivity of monoterpene (α-pinene), and is oxidised in a single-step mechanism with a fixed SOA yield. By using the chemical reactivity of either benzene, toluene or naphthalene for VOCANT/BB, the global annual-total VOCANT/BB oxidation rate changes by -3, -31 or -66 %, respectively, compared to when using monoterpene. Increasing the number of reaction intermediates, by introducing a peroxy radical (RO2), slightly slows the rate of SOA formation, but has no impact on the global annual-total SOA production rate. However, RO2 undergoes competitive oxidation reactions, forming products with substantially different volatilities. Accounting for the differences in product volatility between RO2 oxidation pathways increases the global SOA production rate by 153 % compared to using a single SOA yield. Overall, for relatively reactive compounds, such as toluene and naphthalene, the reduction in reactivity for VOCANT/BB oxidation is outweighed by accounting for the difference in volatility of RO2 products, leading to a net increase in the global annual-total SOA production rate of 85 and 145 %, respectively, and improvemtns in model agreement (NMB of -46 and 56 %, respectively). However, for benzene, the reduction in VOCANT/BB oxidation is not outweighed by accounting for the difference in SOA yield pathways, leading to a small change in the global annual-total SOA production rate of -3 %, and a slight worsening of model agreement with observatiobs (NMB = -77 %). These results highlight that variations in both VOC deposition and oxidation mechanisms contribute to substantial uncertainties in the global SOA budget and model agreement with observations. [ABSTRACT FROM AUTHOR]

Aerosol acidity affects the chemical transformation of aerosols and subsequent haze formation. High resolution (1-h) observation of water-soluble inorganic ions in fine particles, gaseous pollutants, and meteorological parameters was conducted from September 2015 to August 2016 at Wuhan, a megacity of Central China with high relative humidity and ambient temperature, compared with north Chinese cities. By adopting thermodynamic model ISOROPPIA-II, the aerosol acidity for different time scales, pollution episodes, and air mass directions was calculated. Aerosols in Wuhan were moderate acidic, with pH averaged as 3.30 ± 0.49. The aerosol acidity was higher in July (pH as 2.64 ± 0.31), September (pH as 2.75 ± 0.30) and August (pH as 2.79 ± 0.29), and lower in January (pH as 3.77 ± 0.28) and March (pH as 3.70 ± 0.16). It decreased with the air pollution increasing, with the pH values of 3.07 ± 0.45, 3.63 ± 0.27 and 3.84 ± 0.22 for clean, transition and polluted episodes, respectively. The air masses in Wuhan transported from North China exhibited higher aerosol acidity, with pH averaged as 3.17–3.22. The unique environmental and meteorological conditions (high humidity, annual averaged RH as 0.74 ± 0.13) lead to excess ammonium (on average of 6.06 ± 4.51 μg m−3) and abundant aerosol water content (AWC, on average of 71.0 ± 82.8 μg m−3) in Wuhan, which can explain the lower PM2.5 acidity in Wuhan than other megacities of China. At lower AWC level (less than ~ 15 μg m−3), the particle pH showed a decreasing trend with AWC increased. When the AWC continuous increased from ~ 15 to ~ 380 μg m−3, there was an obvious increase of particle pH. Then no significant growth of pH was found when AWC was higher than ~ 380 μg m−3. With atmospheric RH increasing, the aerosol pH exhibited decreasing trend firstly and then increased, with the turning point RH as about 0.48. There was a logarithmic growth of aerosol pH with total NHx (NH3 + NH4+) increasing. From the fitted logarithmic curve, the aerosol pH of Wuhan was at the range of pH rapid growth stage with NHx increasing, indicating that the control of ammonia emission in Wuhan could be an effective way to reduce the aerosol pH and further mitigate air pollution. This paper firstly obtained the aerosol acidity properties at a megacity under abundant ammonium and high humidity with high time-resolution, which is an important supplementary for the current aerosol acidity research around the world. [ABSTRACT FROM AUTHOR]

Open biomass burning (OBB) has significant impacts on air pollution, climate change and potential human health. OBB has raised wide attention but with few focus on the annual variation of pollutant emission. Central and Eastern China (CEC) is one of the most polluted regions in China. This study aims to provide a state-of the-art estimation of the pollutant emissions from OBB in CEC from 2003 to 2015, by adopting the satellite observation dataset (the burned area product (MCD64Al) and the active fire product (MCD14 ML)), local biomass data (updated biomass loading data and high-resolution vegetation data) and local emission factors. Monthly emissions of pollutants were estimated and allocated into a 1 × 1 km spatial grid for four types of OBB including grassland, shrubland, forest and cropland. From 2003 to 2015, the emissions from forest, shrubland and grassland fire burning had a minor annual variation whereas the emissions from crop straw burning steadily increased. The cumulative emissions of OC, EC, CH4, NOX, NMVOC, SO2, NH3, CO, CO2 and PM2.5 were 3.64 × 103, 2.87 × 102, 3.05 × 103, 1.82 × 103, 6.4 × 103, 2.12 × 102, 4.67 × 103, 4.59 × 104, 9.39 × 105 and 4.13 × 102 Gg in these years, respectively. For cropland, corn straw burning was the largest contributor for all pollutant emissions, by 84 %–96 %. Among the forest, shrubland, grassland fire burning, forest fire burning emissions contributed the most and emissions from grassland fire was negligible due to few grass coverage in this region. High pollutant emissions were populated in the connection area of Shandong, Henan, Jiangsu and Anhui, with emission intensity higher than 100 ton per pixel, which was related to the frequent agricultural activities in these regions. The monthly emission peak of pollutants occurred in summer and autumn harvest periods including May, June, September and October, at which period ~ 50 % of pollutants were emitted for OBB. This study highlights the importance in controlling the crops straw burning emission. From December to March of the next year, the crop residue burning emissions decreased, while the emissions from forest, shrubland and grassland exhibited their highest values, leading to another small peak emissions of pollutants. Obvious regional differences in seasonal variations of OBB were observed due to different local biomass types and environmental conditions. Rural population, agricultural output, local burning habits, anthropological activities and management policies are all influence factors for OBB emissions. The successful adoption of double satellite dataset for long term estimation of pollutants from OBB with a high spatial resolution can support the assessing of OBB on regional air-quality, especially for harvest periods or dry seasons. It is also useful to evaluate the effects of annual OBB management policies in different regions. [ABSTRACT FROM AUTHOR]

Black carbon aerosol (BC) is the principle absorber to modify the shortwave radiative balance between the lower atmosphere and the surface in polluted environment, which was in-situ characterized by aircraft measurements using a single particle soot photometer (DMT inc., SP2) throughout the boundary layer up to 3 km over the North China Plain around Beijing megacity. The flights were conducted in both hot season (late spring, Apr.–Jun. 2012, surface temperature > 20 °C, 10 flights) and cold season (winter, Dec. 2016, surface temperature < 5 °C, 6 flights). The BC mass in the daytime well-developed planetary boundary layer (BCPBL) was found to be largely influenced by meteorology which modulated the local emission and regional transport. The BCPBL in hot season showed no apparent vertical gradient or correlation with the PBL height (PBLH); whereas in winter the BCPBL decreased at higher altitude and accumulated towards the surface due to reduced horizontal wind speed at low level, and was anti-correlated with the PBLH. The more homogenous vertical mixing of BCPBL in hot season may result from the stronger convective mixing due to higher surface temperature, in addition the predominant southerly wind may have advected the largely polluted air mass, offsetting its dilution effect; whereas in winter the predominant cleaner air mass from the north had important dilution effect on local emissions. The overall averages showed lower BC mass loading in the surface layer during hot season but similar loadings (3.5–4 µg m−3) in the PBL for both seasons. The highly turbulent air conditions, as frequently observed in the early afternoon during hot season, largely diluted the BC mass down to the background level (~ 0.5 µg m−3); whereas in winter the BCPBL was significantly elevated under dynamic air condition due to efficient transport of polluted air mass from the south. The BCPBL in winter showed systematically larger core size (mass median diameter, MMD = 217 ± 4 nm) than in late spring (209 ± 7 nm), which may be due to a higher contribution from the residential emission sector in cold season. The high BC mass loadings were mostly associated with a high fraction of thick coatings (Fcoating), and the higher air moisture enhanced the coating content of BCPBL. These suggest the primary sources with a range of co-emitted species significantly contributed to the coatings of BC, and the secondary formation which could be enhanced by elevated RH also played important role. The BC after significant removal showed much lower Fcoating (~ 0.06) and smaller core size (MMD ~ 193 nm), implying that the coated and larger BC particle was preferentially removed. The scavenging efficiency of BC in the entrainment zone (EZ) showed positive correlation with the change of coatings between PBL and EZ for both seasons (Fcoating,PBL > Fcoating,EZ), however showed seasonally different behaviors in terms of core size (MMDPBL > MMDEZ in late spring, but the opposite in winter). These results provide the basis to evaluate the BC direct radiative forcing in the polluted planetary boundary layer over this region and also the indirect forcing of BC by interacting with low-level clouds. [ABSTRACT FROM AUTHOR]

During summertime, dust from the Sahara can be efficiently transported westwards within the Saharan Air Layer (SAL). This can lead to high aerosol loadings being observed above a relatively clean marine boundary layer (MBL) in the tropical Atlantic Ocean. These dust layers can impart significant radiative effects through strong visible and IR light absorption and scattering, and can also have indirect impacts by altering cloud properties. The processing of the dust aerosol can result in changes in both direct and indirect radiative effect, leading to significant uncertainty in climate prediction in this region. During August 2015, measurements of aerosol and cloud properties were conducted off the coast of West Africa as part of the ICE-D and AER-D campaign. Observations were obtained over a 4-week period using the FAAM Bae146 aircraft based on Santiago Island, Cabo Verde. Ground based observations were collected from Praia, also located on Santiago Island. The dust in the SAL was mostly sampled in situ at altitudes of 2-4 km, and the potential dust age was estimated by backward trajectory analysis. The particle mass concentration (at diameter d = 0.1-20 μm) decreased with transport time. Mean effective diameter (Deff) for super-micron SAL dust (d = 1-20 μm) was found to be 5-6 μm regardless of dust age, whereas submicron Deff (d = 0.1-1 μm) showed a decreasing trend with longer transport. For the first time, an airborne laser-induced incandescence instrument (the single particle soot photometer, SP2) was deployed to measure the hematite content of dust. For the Sahel-influenced dust in the SAL, the observed hematite mass fraction of dust (FHm) was found to be anti-correlated with the single scattering albedo (SSA, λ = 550 nm, for particles d < 2.5 μm); as potential dust age increased from 2 to 7 days, FHm increased from 2.5 % to 4.5 %, SSA decreased from 0.97 to 0.93 and the derived imaginary part (k) of the refractive index at 550 nm increased from 0.0015 to 0.0035. However the optical properties of Sahara-influenced plumes (not influenced by the Sahel) were independent of dust age and hematite content with SSA ~ 0.95 and k ~ 0.0028. This indicates that the absorbing component of dust may be source-dependent, or that gravitational settling of larger particles may lead to a higher fraction of more absorbing clay-iron aggregates at smaller sizes. Mie calculation using the measured size distribution and size-resolved refractive indices of the absorbing components (black carbon and hematite) reproduces the measured SSA to within ±0.02 for SAL dust, by assuming a goethite/hematite mass ratio of 2. Hematite and goethite constituted 40-80 % of the absorption for particles d < 2.5 μm and black carbon (BC) contributed 10-37 %. This highlights the importance of size-dependent composition in determining the optical properties of dust, and also the contribution from BC within dust plumes. [ABSTRACT FROM AUTHOR]

Oil and natural gas are important energy supply around the world. The exploring, drilling, transportation, and processing in oil-gas regions can release abundant volatile organic compounds (VOCs). To understand the atmospheric behaviors of VOCs in such region, the fifty-six VOCs designed as the photochemical precursors by the United State Environmental Protection Agency were continuously measured for an entire year (September 2014-August 2015) by a set of on-line monitor system at an oil-gas station in northwest China. The VOC concentrations in this study were 1-50 times higher than those measured in many other urban and industrial regions. The VOC compositions were also different from other studies with alkanes contributing up to 87.5 % of the total VOCs in this study. According to the propylene-equivalent concentration and maximum incremental reactivity method, alkanes were identified as the most important VOC groups to the ozone formation potential. The photochemical reaction, meteorological parameters (temperature, relative humidity, pressure, and wind speed) and boundary layer height were found to influence the temporal variations of VOCs at different time scales. The positive matrix factorization analysis showed that the natural gas, fuel evaporation, combustion sources, oil refining process, and asphalt contributed 62.6 %, 21.5 %, 10.9 %, 3.8 %, and 1.3 %, respectively to the total VOCs on the annual average. Clear temporal variations differed from one source to another was observed, due to their differences in source emission strength and the influence of meteorological parameters. Potential source contribution function and contribution weighted trajectory models based on backward trajectories indicated that five identified sources had similar geographic origins. Raster analysis based on CWT analysis indicated that the local emissions contributed 48.4 %-74.6 % to the VOCs. This research filled the gaps in understanding the VOCs in the oil-gas field region, where exhibited different source emission behaviors compared with the urban/industrial regions. [ABSTRACT FROM AUTHOR]

Particulate emissions from biomass burning can both alter the atmosphere's radiative balance and cause significant harm to human health. However, due to the large effect on emissions caused by even small alterations to the way in which a fuel burns, it is difficult to study particulate production of biomass combustion mechanistically and in a repeatable manner. In order to address this gap, in this study, small wood samples sourced from Côte D'Ivoire in West Africa were burned in a highly-controlled laboratory environment. The shape and mass of samples, available airflow and surrounding thermal environment were carefully regulated. Organic aerosol and refractory black carbon emissions were measured in real time using an Aerosol Mass Spectrometer and a Single Particle Soot Photometer, respectively. This methodology produced remarkably repeatable results, allowing aerosol emissions to be mapped directly onto different phases of combustion. Emissions from pyrolysis were visible as a distinct phase before flaming was established. After flaming combustion was initiated, a black-carbon-dominant flame was observed during which very little organic aerosol was produced, followed by a period that was dominated by organic-carbon-producing smouldering combustion, despite the presence of residual flaming. During pyrolysis and smouldering, the two phases producing organic aerosol, distinct mass spectral signatures that correspond to previously-reported variations in biofuel emissions measured in the atmosphere are found. Organic aerosol emission factors averaged over an entire combustion event were found to be representative of the time spent in the pyrolysis and smouldering phases, rather than reflecting a coupling between emissions and the mass loss of the sample. Further exploration of aerosol yields from similarly carefully controlled fires and a careful comparison with data from macroscopic fires and real-world emissions will help to deliver greater constraints on variability of particulate emissions in atmospheric systems. [ABSTRACT FROM AUTHOR]

We profile trace gas and particulate emissions from near-field airborne measurements of discrete smoke plumes in Brazil during the 2012 biomass burning season. The South American Biomass Burning Analysis (SAMBBA) Project conducted during September and October 2012 sampled across two distinct fire regimes prevalent in the Amazon Basin. Combined measurements from a Compact Time Of Flight Aerosol Mass Spectrometer (C-ToF-AMS) and a Single Particle Soot Photometer (SP2) are reported for the first time in a tropical biomass burning environment. Emissions from a mostly-smouldering rainforest wildfire in Rondonia state and numerous smaller flaming Cerrado fires in Tocantins state are presented. While the Cerrado fires appear to be representative of typical fire conditions in the existing literature, the rainforest wildfire likely represents a more extreme example of biomass burning with a bias towards mostly-smouldering emissions. We determined fire integrated modified combustion efficiencies, emission ratios and emission factors for trace gas and particulate components for these two fire types, alongside aerosol microphysical properties. Seven times more black carbon was emitted from the Cerrado fires per unit of fuel combustion (EFBC of 0.13 ± 0.04 g kg-1) compared to the rainforest fire (EFBC of 0.019 ± 0.006 g kg-1) and more than six times the amount of organic aerosol was emitted from the rainforest fire per unit of fuel combustion (EFOC of 5.00 ± 1.58 g kg-1) compared to the Cerrado fires (EFOC of 0.82 ± 0.26 g kg-1). Particulate phase species emitted from the fires sampled are generally lower than those reported in previous studies and in emission inventories, which is likely a combination of differences in fire combustion efficiency and fuel content, along with different measurement techniques. Previous modelling studies focussed on the biomass burning season in tropical South America have required significant scaling of emissions to reproduce in-situ and satellite aerosol concentrations over the region. Our results do not indicate that emission factors used in inventories are biased low, which could be one potential cause of the reported underestimates in modelling studies. This study supplements and updates trace gas and particulate emission factors for fire type specific biomass burning in Brazil for use in weather and climate models. The study illustrates that initial fire conditions can result in substantial differences in terms of their emitted chemical components, which can potentially perturb the Earth system. [ABSTRACT FROM AUTHOR]

Cyperus esculentus is unique in that it can accumulate rich oil in its tubers. However, the underlying mechanism of tuber oil biosynthesis is still unclear. Our transcriptional analyses of the pathways from pyruvate production up to triacylglycerol (TAG) accumulation in tubers revealed many distinct species-specific lipid expression patterns from oil seeds and fruits, indicating that in C. esculentus tuber: (i) carbon flux from sucrose toward plastid pyruvate could be produced mostly through the cytosolic glycolytic pathway; (ii) acetyl-CoA synthetase might be an important contributor to acetyl-CoA formation for plastid fatty acid biosynthesis; (iii) the expression pattern for stearoyl-ACP desaturase was associated with high oleic acid composition; (iv) it was most likely that endoplasmic reticulum (ER)-associated acyl-CoA synthetase played a significant role in the export of fatty acids between the plastid and ER; (v) lipid phosphate phosphatase (LPP)-δ was most probably related to the formation of the diacylglycerol (DAG) pool in the Kennedy pathway; and (vi) diacylglyceroltransacylase 2 (DGAT2) and phospholipid:diacylglycerolacyltransferase 1 (PDAT1) might play crucial roles in tuber oil biosynthesis. In contrast to oil-rich fruits, there existed many oleosins, caleosins and steroleosins with very high transcripts in tubers. Surprisingly, only a single ortholog of WRINKLED1 (WRI1)-like transcription factor was identified and it was poorly expressed during tuber development. Our study not only provides insights into lipid metabolism in tuber tissues, but also broadens our understanding of TAG synthesis in oil plants. Such knowledge is of significance in exploiting this oil-rich species and manipulating other non-seed tissues to enhance storage oil production. [ABSTRACT FROM AUTHOR]