Nitro-aromatic compounds (NACs) are an important part of brown carbon because of their strong light absorbing properties in the visible and near ultraviolet regions. In this study, the concentration ...and formation mechanism of eight NACs, as well as their relative contribution to the light absorption of methanol-extracted BrC, were determined from fine particle samples collected in Beijing using ultra-high performance liquid chromatography coupled with high resolution mass spectrometry and ultraviolet–visible light spectrophotometry. The average concentrations of the eight NACs were 20.27 ± 12.40 ng m−3 and 74.17 ± 50.66 ng m−3 in autumn and winter, respectively. Among the detected NACs, 4-nitrophenol (4NP) and 4-nitrocatechol (4NC) were the most abundant compounds. The correlation analysis showed that the NACs other than 2,4-dinitrophenol (2,4-DNP) are strongly intercorrelated. Significant correlations among nitro catechols (NCs), nitro salicylic acids (NSAs) and NO2 support their proposed origin from secondary formation in the presence of •OH + NO2 (daytime process) or •NO3+NO2 (nighttime process). Significant correlations among nitrate, sulfate and NSAs were also found, indicating that the nitration of salicylic acid by nitric acid and sulfuric acid was another possible mechanism formation of NSAs. The methanol-extracts in winter had much higher light absorption than those in autumn, which is in agreement with the trend of NACs but contrary to the trends of PM2.5, water soluble ions, organic carbon and elemental carbon. The average absorption Ångström exponents (AAEs) during autumn and winter were 4.62 and 5.55, respectively, suggesting that secondary transformation were the main sources of BrC. The light absorption of NACs accounted for 1.17% and 3.18% of the total methanol-soluble BrC light absorption at λ = 365 nm in autumn and winter, respectively, while their masses only accounted for 0.16% and 0.44% of the OC, respectively, demonstrating that although NACs are not the major contributor to BrC, but they are strong BrC chromophores, and their influence on solar radiation should be included in future modeling work.
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•Absorption characteristics of methanol-extracted BrC have been analyzed during autumn and winter of Beijing.•Concentration and possible sources of NACs have been analyzed in autumn and winter in Beijing.•Nitration by NO2 and nitrate has been discussed through the correlation analysis with NO2, NO3− and pHin situ.•Contributions of NACs to the light absorption of methanol-soluble BrC were estimated.
PM2.5-bound polycyclic aromatic hydrocarbons (PAHs) during winter 2015 at three urban sites, including Beijing, Tianjin and Shijiazhuang, and one background site (Xinglong) over the North China Plain ...(NCP) were investigated. The spatial variations of PAHs showed the same trends with PM2.5 mass concentrations, i.e. the highest PAHs concentrations was in Shijiazhuang, followed by Tianjin, Beijing and the lowest PAHs concentrations was in Xinglong. The diurnal variations of PAHs exhibited PAHs concentrations during nighttime were higher than those during daytime. The dominant species in PAHs were fluranthene and benzob + kfluoranthene, indicating that diesel vehicle emission, coal combustion and biomass burning could be important and potential sources for PAHs over the NCP. There results were supported by diagnostic ratios analysis. But coefficient of divergence analysis showed that a high extent of spatial contrast among four sampling sites, except between Beijing and Tianjin. Analysis of toxicity equivalent quantities (TEQ) and the lifetime excess cancer risk (ECR) from inhalation exposure to PAHs showed that 818, 1517, 5129 and 182 cases per 100,000 people exposed in Beijing, Tianjin, Shijiazhuang and Xinglong, respectively, which were much higher than the threshold value suggested by US-EPA, i.e. 1 case per 100,000 people, and indicating that the NCP suffered from very serious health risk from PAHs, especially in Shijiazhuang.
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•PAHs had higher mass concentrations at urban sites than those at background site.•BaP concentrations at three urban sites were much higher than WHO and NAAQ standards.•Fossil fuel combustion, biomass and coal combustion were the main sources of PAHs over the NCP.•Toxicity equivalent quantities based on PAHs revealed a high health risk to residents over the NCP.
Size-segregated water-soluble ionic species (WSIs) were measured using an Anderson cascade impactor from Jul. to Aug. 2008 and from Dec. 2009 to Feb. 2010 in urban Beijing. The results showed that ...fine particles (PM2.1, Dp < 2.1 μm) accounted for ∼49% (summer) and ∼34% (winter) of the total particulate mass, and WSIs accounted for 23–82% of the mass concentration of PM2.1. Secondary inorganic aerosols (SIAs, the sum of SO42−, NO3− and NH4+) accounted for more than 30% of the fine particles, which were greatly elevated during particle pollution events (PM events), thereby leading to an alteration of the size distributions of SO42− and NO3− to nearly single fine-mode distributions peaking at 0.65–2.1 μm. This finding suggests that heterogeneous aqueous reactions were enhanced at high RH values. SIAs also increased during dust events, particularly for coarse mode SO42−, which indicated enhanced heterogeneous reactions on the dust surface. The positive matrix factorization (PMF) model was used to resolve the bulk mass size distributions into condensation, droplet, and coarse modes, representing the three major sources of the particles. The formation of SO42− was attributed primarily to in-cloud or aerosol droplet processes during summer (45%), and the heterogeneous reaction of SO2 on mineral dust surfaces was an important formation pathway during winter (45%). The formation pathways of NO3− in fine particles were similar to those of SO42−, where over 30% were formed by in-cloud processes. This work provides important field measurement-based evidence for understanding the formation pathway of secondary inorganic aerosols in the megacity of Beijing.
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•SIA in the range of 0.65–2.1 μm exhibited the most dramatic increase in PM events.•Dust particles enhance sulfate and nitrate concentration in fine and coarse particles.•The formation of SIA in fine particles was mainly attributed to in-cloud process.•The coarse mode nitrate formation was different from sulfate.
Public concerns over airborne trace elements (TEs) in metropolitan areas are increasing, but long-term and multi-site observations of size-resolved aerosol TEs in China are still lacking. Here, we ...identify highly elevated levels of atmospheric TEs in megacities and industrial sites in a Beijing–Tianjin–Hebei urban agglomeration relative to background areas, with the annual mean values of As, Pb, Ni, Cd and Mn exceeding the acceptable limits of the World Health Organization. Despite the spatial variability in concentrations, the size distribution pattern of each trace element was quite similar across the region. Crustal elements of Al and Fe were mainly found in coarse particles (2.1–9μm), whereas the main fraction of toxic metals, such as Cu, Zn, As, Se, Cd and Pb, was found in submicron particles (<1.1μm). These toxic metals were enriched by over 100-fold relative to the Earth's crust. The size distributions of Na, Mg, K, Ca, V, Cr, Mn, Ni, Mo and Ba were bimodal, with two peaks at 0.43–0.65μm and 4.7–5.8μm. The combination of the size distribution information, principal component analysis and air mass back trajectory model offered a robust technique for distinguishing the main sources for airborne TEs, e.g., soil dust, fossil fuel combustion and industrial emissions, at different sites. In addition, higher elemental concentrations coincided with westerly flow, indicating that polluted soil and fugitive dust were major sources of TEs on the regional scale. However, the contribution of coal burning, iron industry/oil combustion and non–ferrous smelters to atmospheric metal pollution in Northern China should be given more attention. Considering that the concentrations of heavy metals associated with fine particles in the target region were significantly higher than those in other Asian sites, the implementations of strict environmental standards in China are required to reduce the amounts of these hazardous pollutants released into the atmosphere.
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•Trace elements of size-resolved aerosols were measured in an urban agglomeration.•Aerosol heavy metals were enriched by over 100-fold relative to the Earth's crust.•The annual mean As, Pb, Cd and Mn concentrations in the air exceeded the WHO limits.•High levels of elements with westerly winds indicated that the major source is soil.•Fossil fuel burning and industrial processes contributed to aerosol metal pollution.
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•The domain-averaged PM2.5 in North China decreased significantly from 2013 to 2017.•Firstly established two automatic algorithms to identify regional pollution types and events.•The ...relationships of synoptic circulations and regional PM2.5 levels were quantified.•Starting areas, synoptic and local meteorological mechanisms were analyzed based on persistent regional pollution events.•Quantifying the effects of weather changes on the interannual PM2.5 variations.
In the last decade, North China (NC) has been one of the most populated and polluted regions in the world. The regional air pollution has had a serious impact on people’s health; thus, all levels of government have implemented various pollution prevention measures since 2013. Based on multi-city in situ environmental and meteorological data, as well as the meteorological reanalysis dataset from 2013 to 2017, regional pollution characteristics and meteorological formation mechanisms were analyzed to provide a more comprehensive understanding of the evolution of PM2.5 in NC. The domain-averaged PM2.5 was 79 ± 17 µg m−3 from 2013 to 2017, with a decreasing rate of 10 μg m−3 yr−1. Two automatic computer algorithms were established to identify 6 daily regional pollution types (DRPTs) and 48 persistent regional pollution events (PRPEs) over NC during 2014–2017. The average PM2.5 concentration for the Large-Region-Pollution type (including the Large-Moderate-Region-Pollution and Large-Severe-Region-Pollution types) was 113 ± 40 µg m−3, and more than half of Large-Region-Pollution days and PRPEs occurred in winter. The PRPEs in NC mainly developed from the area south of Hebei. The number of Large-Region-Pollution days decreased notably from 2014 to 2017, the annual number of days varying between 194 and 97 days, whereas a slight decline was observed in winter. In addition, the averaged PM2.5 concentrations and the numbers and durations of the PRPEs decreased. Lamb-Jenkinson weather typing was used to reveal the impact of synoptic circulations on PM2.5 across NC. Generally, the contributions of the variations in circulation to the reduction in PM2.5 levels over NC between 2013 and 2017 were 64% and 45% in summer and winter, respectively. The three most highly polluted weather types were types C, S and E, with an average PM2.5 concentration of 137 ± 40 µg m−3 in winter. Furthermore, three typical circulation dynamics were categorized in the peak stage of the PRPEs, namely, the southerly airflow pattern, the northerly airflow pattern and anticyclone pattern; the averaged relative humidity, recirculation index, wind speed and boundary layer height were 63%, 0.33, 2.0 m s−1 and 493 m, respectively. Our results imply that additional emission reduction measures should be implemented under unfavorable meteorological situations to attain ambient air quality standards in the future.
Polycyclic aromatic hydrocarbons (PAHs) associated with size-segregated particulate matter at 10 sampling sites over China which can be grouped into North China and South China, including urban site, ...sub-urban site, farmland site and background site, from January 2013 to December 2014 were analyzed by Gas Chromatography – Mass Spectrometry. This is the first time for comprehensive studies on the size-segregated PAHs at the national level. The spatial variations of particulate PAHs showed that Xinaghe (XH), Yucheng (YC) and Shenyang (SHY) in North China had higher particulate PAHs mass concentrations than other sampling sites. The seasonal variations of PAHs exhibited the highest mass concentrations in winter, which could be caused by the increase in emission, lower temperatures and weaker solar radiation. Particulate PAHs were found to be dominant in fine size range of <1.1 μm, the same as individual PAH compounds. The dominant species in particulate PAHs are benzob + kfluoranthene (BBKF), indeno1,2,3-cdpyrene (IP) and benzog,h,iperylene (BghiP), indicating that fossil fuel combustion could be an important source for PAHs over China. BaP, a carcinogen to humans, also had much higher mass concentrations at XH, SHY and YC in North China than other sites. Toxicity equivalent quantities (TEQ) and the lifetime excess cancer risk (ECR) analysis showed that XH, SHY and YC in North China suffered more serious health risk from PAHs than other sites. In addition, higher TEQ and higher ECR were found in the size range of <1.1 μm, indicating that finer particles are associated with higher toxicity.
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•PAHs over China concentrated in the finer size range of <1.1 μm.•BBKF, IP and BghiP were dominant species in PAHs, indicating coal combustion and traffic could be important sources for PAHs.•Lifetime excess cancer risk over China is much higher than the threshold value of US-EPA.
North China registers frequent air pollution episodes from high PM2.5 concentrations. Shijiazhuang is located at the intensive industrial zone of this region, but there is insufficient data on the ...chemical composition of PM2.5 and its sources in this city. In this study, the chemical and seasonal characteristics of PM2.5 in Shijiazhuang were investigated based on 12-h integrated PM2.5 measurements made over eight 1-month periods in each season between June 2014 and April 2016 (486 samples). The eight-season average concentration of PM2.5 was 138.8 μg m−3, and the major chemical components were secondary inorganic aerosol (SIA) species of sulfate, nitrate, and ammonium (41.5%), followed by organic matter (25.9%). The mass concentration and most of the chemical components of PM2.5 showed clear seasonal variation, with a winter-high and summer-low pattern. SO42− and NO3− were the dominant components at each pollution level in summer and autumn (18.1%–30.6% and 14.2%–27.0%, respectively). Sufficient gaseous oxidants (O3) concentrations and suitable meteorology conditions were observed in these two seasons. Highest SOR (0.61), SO42−/EC(10.8) and NOR (0.58), NO3−/EC (5.9) were found in summer and autumn, which indicated intense secondary transformation in these two seasons. Organic matter was the dominant species in winter, which increased from 17.1 μg m−3 for clean days (28.7% of PM2.5) to 169.1 μg m−3 (38.4% of PM2.5). The accumulation of primary emissions (coal combustion and biomass burning) was responsible for the increasing OM trend (especially for POC). The highest and leading proportion of mineral dust occurred in spring (20.3%–46.5%) as a result of higher wind speeds (up to 3 m/s). Potential source contribution function (PSCF) analyses implied that the border areas of Hebei, Henan and Shandong Provinces, together with the central area of Shanxi Province, contributed significantly to the PM2.5 pollution in Shijiazhuang, especially in autumn and winter.
Major components (SO42−, NO3−, primary organic carbon (POC), secondary organic carbon (SOC) and mineral dusts) of PM2.5, SOR and NOR at different pollution level of each season.
C: Clean days; SL: Slightly polluted days; MP: Moderately polluted days; HP: Heavily polluted days; SEP: Severely polluted days. Display omitted
•SIA and OM were the major components of PM2.5 in Shijiazhuang.•High atmospheric oxidation was conducive to form SIA in summer and autumn.•Biomass burning and coal combustion contributed to the high OM in autumn and winter.•Regional transportation contributed significantly to the PM2.5 pollution in Shijiazhuang.
The tumor immune response has been proven critical to prognosis in colorectal cancer (CRC), but studies on the prognostic role of neutrophil infiltration have shown contradictory results. The aim of ...this study was to elucidate the prognostic role of infiltrating neutrophils at different intratumoral subsites and in different molecular subgroups of CRC. The relations between neutrophil infiltration and infiltration of other immune cells (T-cell and macrophage subsets) were also addressed. Expression of the neutrophil marker CD66b was assessed by immunohistochemistry in 448 archival human tumor tissue samples from patients surgically resected for CRC. The infiltration of CD66b-positive cells was semi-quantitatively evaluated along the tumor invasive front, in the tumor center, and within the tumor epithelium (intraepithelial expression). We found that poor infiltration of CD66b-positive cells in the tumor front indicated a worse patient prognosis. The prognostic significance of CD66b infiltration was found to be mainly independent of tumor molecular characteristics and maintained significance in multivariable analysis of stage I-II colon cancers. We further analyzed the prognostic impact of CD66b-positive cells in relation to other immune markers (NOS2, CD163, Tbet, FOXP3, and CD8) and found that neutrophil infiltration, even though strongly correlated to infiltration of other immune cell subsets, had additional prognostic value. In conclusion, we find that low infiltration of neutrophils in the tumor front is an independent prognostic factor for a poorer patient prognosis in early stages of colon cancers. Further studies are needed to elucidate the biological role of neutrophils in colorectal carcinogenesis.
•Neutrophil infiltration is a favorable prognostic factor in stage I-II colon cancers.•The prognostic value of neutrophils is dependent on intratumoral subsite.•The prognostic role of neutrophils is independent of tumor molecular features.•Neutrophils likely play a role in the anti-tumor immune response.
To investigate the characteristics of aerosols in north China, the samples of water-soluble ions, including anions (F−, Cl−, NO2−, NO3−, SO42−) and cations (NH4+, K+, Na+, Ca2+, Mg2+) in 8 ...size-segregated particle fractions, are collected using a sampler from Sep. 2009 to Aug. 2010 at four sites in urban areas (Beijing, Tianjin and Tangshan) and a background region (Xinglong) in the Jing-Jin-Ji urban agglomeration. High spatial variability is observed between the urban areas and the background region. The results of chemical composition analysis showed that secondary water soluble ions (SO42− + NO3− + NH4+) (SWSI) composed more than half the total ions, and are mainly found in fine particles (aerodynamic diameters less than 2.1 μm), while Mg2+ and Ca2+ contributed to a large fraction of the total water-soluble ions in coarse particles (aerodynamic diameters greater than 2.1 μm and less than 9.0 μm). The concentrations of SO42−, NO3− and NH4+ are higher in summer and winter and lower in spring and autumn. Mg2+ and Ca2+ are obviously abundant in winter in Beijing, Tianjin and Tangshan. In contrast, Mg2+ and Ca2+ are abundant in autumn in Xinglong. The SWSI showed a bimodal size distribution with the fine mode at 0.43–1.1 μm and the coarse mode at 4.7–5.8 μm, and had different seasonal variations and bimodal shapes. NH4+ played an important role in the size distributions and the formations of SO42− and NO3−. Heterogeneous reaction is the main formation mechanism of SO42− and NO3−, which tended to be enriched in the coarse mode of aerosol. The sulfur oxidation ratio (SOR) and nitrogen oxidation ratio (NOR) indicated high photochemical oxidation property over the whole Jing-Jin-Ji urban agglomeration.
•The concentrations of water-soluble ions in the Jing-Jin-Ji urban agglomeration.•The spatial variability of those compounds was discussed.•The seasonal variations and size distributions of those compounds were discussed.•The sources and formation mechanisms of secondary water-soluble ions were discussed.
To investigate the characteristics of atmospheric brown
carbon (BrC) in the semiarid region of East Asia, PM2.5 and
size-resolved particles in the urban atmosphere of Xi'an, inland China,
during the ...winter and summer of 2017 were collected and analyzed for optical
properties and chemical compositions. Methanol extracts (MeOH extracts) were
more light-absorbing than water extracts (H2O extracts) in the optical
wavelength of 300–600 nm and well correlated with nitrophenols, polycyclic
aromatic hydrocarbons (PAHs) and oxygenated PAHs (r > 0.78). The
light absorptions (absλ=365 nm) of H2O extracts and
MeOH extracts in winter were 28±16 and 49±32 M m−1,
respectively, which are about 10 times higher than those in summer, mainly
due to the enhanced emissions from biomass burning for house heating. Water-extracted BrC predominately occurred in the fine mode (< 2.1 µm) during winter and summer, accounting for 81 % and 65 % of the total
absorption of BrC, respectively. The light absorption and stable carbon
isotope composition measurements showed an increasing ratio of absλ=365 nm-MeOH to absλ=550 nm-EC along with an enrichment of
13C in PM2.5 during the haze development, indicating an
accumulation of secondarily formed BrC (e.g., nitrophenols) in the aerosol aging
process. Positive matrix factorization (PMF) analysis showed that biomass burning, fossil fuel combustion,
secondary formation, and fugitive dust are the major sources of BrC in the
city, accounting for 55 %, 19 %, 16 %, and 10 % of the total BrC of
PM2.5, respectively.
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