Wuhan was the first city to adopt the lockdown measures to prevent COVID-19 spreading, which improved the air quality accordingly. This study investigated the variations in chemical compositions, ...source contributions, and regional transport of fine particles (PM2.5) during January 23–February 22 of 2020, compared with the same period in 2019. The average mass concentration of PM2.5 decreased from 72.9 μg m−3 (2019) to 45.9 μg m−3 (2020), by 27.0 μg m−3. It was predominantly contributed by the emission reduction (92.0%), retrieved from a random forest tree approach. The main chemical species of PM2.5 all decreased with the reductions ranging from 0.85 μg m−3 (chloride) to 9.86 μg m−3 (nitrate) (p < 0.01). Positive matrix factorization model indicated that the mass contributions of seven PM2.5 sources all decreased. However, their contribution percentages varied from −11.0% (industrial processes) to 8.70% (secondary inorganic aerosol). Source contributions of PM2.5 transported from potential geographical regions showed reductions with mean values ranging from 0.22 to 4.36 μg m−3. However, increased contributions of firework burning, secondary inorganic aerosol, road dust, and vehicle emissions from transboundary transport were observed. This study highlighted the complex and nonlinear response of chemical compositions and sources of PM2.5 to air pollution control measures, suggesting the importance of regional-joint control.
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•Differences in PM2.5 chemical species and sources since lockdown were reported.•Primary emission reduced while secondary formation enhanced since lockdown.•Emission reduction dominated the improvement of air quality in Wuhan during lockdown.
Abstract
The result of Aethalometer model to black carbon (BC) source apportionment is highly determined by the absorption Ångström exponent (
α
) of aerosols from fossil fuel combustion (
α
ff
) and ...wood burning (
α
wb
). A method using hourly measured potassium to calculate the
α
ff
and
α
wb
values was developed in this study. Results showed that the optimal
α
ff
and
α
wb
were 1.09 and 1.79 for the whole dataset. The optimal
α
values in the diurnal resolution were also calculated with
α
ff
and
α
wb
varied in 1.02 –1.19 and 1.71–1.90, respectively. Using the dynamic
α
values, the Pearson correlation coefficient between BC and potassium from wood burning substantially improved compared to the results derived from the fixed
α
values. The method developed in this study is expected to provide more reasonable BC source identification results, which are helpful for air quality, climate, and human health modeling studies.
Source profiles of volatile organic compounds (VOCs) emitted from the evaporation of various fuels, industrial raw materials, processes and products are still limited in China. The impact of ambient ...temperature on the VOC released from these fugitive emission sources has also been rarely reported. In order to establish VOC source profiles for thirteen volatile emission sources, a sampling campaign was conducted in Central China, and five types of sources were investigated both in winter and summer. The dominant VOC groups varied in different sources, and they were alkanes (78.6%), alkenes (53.1%), aromatics (55.1%), halohydrocarbons (80.7%) and oxygenated VOCs (OVOCs) (76.0%), respectively. Ambient temperature showed different impacts on VOC source profiles and specific species ratios. The mass percentages of halohydrocarbons emitted from color printing and waste transfer station in summer were 42 times and 20 times higher than those in winter, respectively. The mass percentages of OVOCs emitted from car painting, waste transfer station and laundry emission sources were much higher in summer (7.9–27.8%) than those in winter (0.8–2.6%). On the contrary, alkanes from color printing, car painting and waste transfer stations were about 11, 4 and 5 times higher in winter than those in summer, respectively. The coefficient of divergence values for the source profiles obtained in winter and summer ranged in 0.3–0.7, indicating obvious differences of source profiles. Benzene/toluene ratio varied in 0.00–0.76, and it was in the range of 0.02–0.50 in winter and 0.04–0.52 in summer for the same sources, respectively. Hexanal, isobutene, m,p-xylene, toluene, 2-methylacrolein, styrene, 1-hexane and cis-2-butene dominated the ozone formation potentials (OFP). The OFP summer/winter differences were 5–320 times by MIR method and 1–79 times by Propy-Equiv method, respectively. This study firstly gave direct evidence that ambient temperature modified the mass percentages of VOC species obviously. It is important for improving VOC source apportionment and chemical reactivity simulation.
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•Source profiles of VOCs for thirteen volatile emission sources were established.•Ambient temperature substantially impacts the VOC source profiles.•Benzene/toluene diagnostic ratio varied for different sources and periods.•Ozone formation potential and indicatory VOCs varied between winter and summer.
Accurate source markers, source profiles and species-based emission factors (EFs) are currently the key limitations for source apportionment and emission inventory researches. Fine particles (PM2.5) ...were collected from stack gases of eight types of stationary sources with a dilution sampling system. The mass percentages and EFs of 89 kinds of chemical species in PM2.5 including water-soluble ions, elements, carbonaceous species and molecular organic species were obtained. Results showed that water-soluble ions (8%–54%) and elements (5%–45%) were the dominant chemical species. Palmitic acid (0.19%–0.62%) and stearic acid (0.21%–0.59%) were the most abundant organic species. PM2.5 source profiles of the eight sources were different from each other with the coefficient of divergence values all higher than 0.4. The addition of organic species could help to further distinguish them. The indicatory chemical components and specific species ratios were obtained by both a statistical equation and randomForest. These indicatory chemical components (e.g. F− for glass factory) and species ratios (e.g. K+/Mg2+ & OC/Mg for pharmaceutical factory) improved the current knowledges of their indicatory performance in source identification of ambient PM2.5. The EFs of PM2.5 from the eight stationary sources ranged from 0.019 to 51.6 kg t−1 of fuel used. The EFs of PM2.5 from the pharmaceutical factory were about 70–2600 times higher than other seven types of sources due to the lack of dust-removing devices. Certain EFs measured in this study were about 10–36,000 times lower than corresponding EFs estimated in previous studies which didn't perform field measurements, indicating the necessity for improving emission inventories continuously. This study contributes to identifying emission sources of PM2.5 especially for subtypes of stationary sources and to establishing species-based emission inventories.
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•Eighty-nine organic/inorganic species in PM2.5 from stationary sources were detected.•Organic species could help to further distinguish the stationary sources.•Indicatory components and ratios were estimated by the equation and randomForest.•Emission factors of components and PM2.5 from stationary sources were provided.
Aerosol size distribution, chemical components and their mixing state are key factors impacting the optical properties of aerosols. The researches on optical properties closure and sources for ...size-segregated aerosols are still scattered. A sampling campaign covering a summer harvest period was conducted in Nanjing, considering the influence of open biomass burning (BB) on optical properties of size-resolved aerosol. Two parallel FA-3 samplers were employed to collect nine size-segregated particles (0.43–10 μm), with water-soluble ions, carbonaceous components and elements analyzed. Aerosol light absorption (bap) and scattering (bsp) coefficients were synchronously online monitored. Results indicated that sulfate, nitrate and ammonium (SNA), crustal materials (CM) and organic matter (OM) were the main contributors of aerosol mass, totally accounting for 61.3%–81.4%. On hazy days, PM1.1 occupied 82.3% of the total estimated bsp by Mie model, with SNA and OM accounting for 40.9% and 16.2%, respectively. PM1.1 contributed 61.7% of the total estimated bap with EC accounting for 41.6%. Positive matrix factorization modeling indicated that vehicle emission contributed most (13.1%–52.9%) to bap especially for particles with diameter smaller than 0.43 μm. On hazy days, BB was the main source for bsp, contributing to 24.7% (for particle within 1.1–2.1 μm)-38.2% (0.65–1.1 μm), then followed by secondary inorganic aerosol, contributing to 16.3% (1.1–2.1 μm)-18.8% (0.65–1.1 μm). For the summer harvest period, the open BB impacts obviously on bsp rather than bap, promoting the haze formation. The temporal variations of aerosol externally mixed ratio and significant negative correlations between the mixed ratio and OC/EC also verified that fresh BB emissions deteriorated the visibility. This study highlights the different roles of aerosol chemical components and emission sources impacting optical properties for size-resolved aerosols, which is helpful to give more accurate visibility improvement strategies.
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•Research Highlight:•Mass and optical properties closures for size-resolved aerosols were investigated.•Sources of optical properties for size-resolved aerosols were apportioned.•Impacts of BB on optical properties for size-resolved aerosols were quantified.
Wuhan was the first city to adopt the lockdown measures to prevent COVID-19 spreading, which improved the air quality accordingly. This study investigated the variations in chemical compositions, ...source contributions, and regional transport of fine particles (PM
) during January 23-February 22 of 2020, compared with the same period in 2019. The average mass concentration of PM
decreased from 72.9 μg m
(2019) to 45.9 μg m
(2020), by 27.0 μg m
. It was predominantly contributed by the emission reduction (92.0%), retrieved from a random forest tree approach. The main chemical species of PM
all decreased with the reductions ranging from 0.85 μg m
(chloride) to 9.86 μg m
(nitrate) (p < 0.01). Positive matrix factorization model indicated that the mass contributions of seven PM
sources all decreased. However, their contribution percentages varied from -11.0% (industrial processes) to 8.70% (secondary inorganic aerosol). Source contributions of PM
transported from potential geographical regions showed reductions with mean values ranging from 0.22 to 4.36 μg m
. However, increased contributions of firework burning, secondary inorganic aerosol, road dust, and vehicle emissions from transboundary transport were observed. This study highlighted the complex and nonlinear response of chemical compositions and sources of PM
to air pollution control measures, suggesting the importance of regional-joint control.
The control of multimetallic ensembles at the atomic‐level is challenging, especially for high‐entropy alloys (HEAs) possessing five or more elements. Herein, the one‐pot synthesis of ...hexagonal‐close‐packed (hcp) PtRhBiSnSb high‐entropy intermetallic (HEI) nanoplates with intrinsically isolated Pt, Rh, Bi, Sn, and Sb atoms is reported, to boost the electrochemical oxidation of liquid fuels. Taking advantage of these combined five metals, the well‐defined PtRhBiSnSb HEI nanoplates exhibit a remarkable mass activity of 19.529, 15.558, and 7.535 A mg−1Pt+Rh toward the electrooxidation of methanol, ethanol, and glycerol in alkaline electrolytes, respectively, representing a state‐of‐the‐art multifunctional electrocatalyst for alcohol oxidation reactions. In particular, the PtRhBiSnSb HEI achieves record‐high methanol oxidation reaction (MOR) activity in an alkaline environment. Theoretical calculations demonstrate that the introduction of the fifth metal Rh enhances the electron‐transfer efficiency in PtRhBiSnSb HEI nanoplates, which contributes to the improved oxidation capability. Meanwhile, robust electronic structures of the active sites are achieved due to the synergistic protections from Bi, Sn, and Sb sites. This work offers significant research advances in developing well‐defined HEA with delicate control over compositions and properties.
High‐entropy PtRhBiSnSb intermetallic nanoplates with intrinsically isolated Pt/Rh/Bi/Sn/Sb atoms are successfully constructed via a one‐pot method. Benefiting from the synergism of the chosen five elements, these well‐defined PtRhBiSnSb intermetallic nanoplates achieve ultrahigh performance toward the electrochemical oxidation of methanol, ethanol, and glycerol in alkaline electrolytes, emerging as a state‐of‐the‐art multifunctional electrocatalyst for the alcohol oxidation reactions.
The 180° curvature of the Banda arc at the eastern end of the Java‐Banda subduction zone reflects complicated geodynamic processes. A detailed investigation of its anisotropic structure would reveal ...its subduction dynamics, further resolving the controversial issue on how the highly arcuate Banda arc formed. We apply tilting‐axis anisotropic tomography to obtain a high‐resolution 3‐D anisotropic model beneath the Java‐Banda region. Our results show significant differences between Java and Banda in the pattern of anisotropy in both the subducting slab and its surrounding mantle, which reflect two distinctly different deformation modes in the two domains. Our results support the single‐slab subduction model for the Banda region. In addition, trench‐normal and upright fast‐velocity‐planes appear in the deep upper mantle, which may indicate material migrations in the big mantle wedge. Fast‐velocity‐planes in the shallow mantle exhibit a toroidal distribution, reflecting past counter‐clockwise rotation and asthenospheric material extrusion.
Plain Language Summary
How the great curvature of the Banda arc formed remains in debate. Previous studies have proposed a single slab model and a double slab model for this subduction zone. Seismic anisotropy in the subducting slab and its surrounding mantle could provide clues on which model is correct. In this work, we perform the first tomographic inversion for tilting‐axis anisotropy to reveal the 3‐D anisotropic structure of the Java‐Banda subduction zone. The anisotropic features in the subducted slab and its surrounding mantle revealed by our anisotropic tomography support the single‐slab subduction model for the formation of the Banda arc.
Key Points
Significant anisotropic differences exist between Java and Banda in both the mantle and slab
Slab subduction is the main cause of seismic anisotropy in the Java‐Banda arc
Our results support the single slab model for the Banda subduction zone
Engineering multicomponent nanocatalysts is effective to improve electrocatalysis in many applications, yet it remains a challenge in constructing well‐defined multimetallic active sites at the ...atomic level. Herein, the surface inlay of sub‐monolayer Pb oxyhydroxide onto hexagonal PtBi intermetallic nanoplates with intrinsically isolated Pt atoms to boost the methanol oxidation reaction (MOR) is reported. The well‐defined PtBi@6.7%Pb nanocatalyst exhibits 4.0 and 7.4 times higher mass activity than PtBi nanoplates and commercial Pt/C catalyst toward MOR in the alkaline electrolyte at 30 °C. Meanwhile, it also achieves a record‐high mass activity of 51.07 A mg–1Pt at direct methanol fuel cells operation temperature of 60 °C. DFT calculations reveal that the introduction of Pb oxyhydroxide on the surface not only promotes the electron transfer efficiency but also suppresses the CO poisoning effect, and the efficient p‐d coupling optimizes the electroactivity of PtBi@6.7%Pb nanoplates toward the MOR process with low reaction barriers. This work offers a nanoengineering strategy to effectively construct and modulate multimetallic nanocatalysts to improve the electroactivity toward the MOR in future research.
Hexagonal PtBi intermetallic nanoplates inlaid with sub‐monolayer Pb oxyhydroxide are constructed and resolved at the atomic level. Originating from the isolation and surface modification of Pt atoms via Bi/Pb species, the well‐defined PtBi@6.7%Pb nanoplates exhibit significantly enhanced activity, durability, and anti‐CO poisoning toward the methanol electro‐oxidation in alkaline electrolyte, and the notable effects of Pb oxyhydroxide patching are revealed by DFT calculations.
The Java subduction zone is located in the southern part of Southeast Asia, where the strong plate convergence results in clustered arc volcanoes and intense seismicity. To better understand the arc ...magmatism and seismogenesis in this region, we determine a high-resolution 3-D P-wave velocity (Vp) model of the crust and upper mantle down to 600 km depth beneath Java. The geometry of the subducting Australian slab is taken into account in the starting model to obtain a better tomographic result by inverting a large number of travel-time data of local and teleseismic events. Our results show lower intra-slab Vp anomalies at depths of ∼100–200 km than other parts of the slab, which may reflect dehydration embrittlement and a slab hole. Feeble low-Vp anomalies appear below the subducting Australian slab, which is probably due to the slab hole where subslab hot materials flow into the mantle wedge. This feature may be related to the occurrence of potassium-rich back-arc volcanoes and the lack of giant megathrust earthquakes (Mw ≥ 8.5) in Java. Our tomographic results also support the hot finger model for explaining the arc magmatism in Java.
•A detailed 3-D P wave velocity model of the Java subduction zone is determined.•The distribution pattern of low-velocity zones in the mantle wedge supports the hot finger model.•A lower-Vp anomaly exists within the high-V slab that is smaller than the well-known seismicity gap.
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