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Mitigating NOX emissions does not help alleviate wintertime particulate pollution in Beijing-Tianjin-Hebei, China
No full textStringent mitigation measures have reduced wintertime fine particulate matter (PM2.5) concentrations by 42.2% from 2013 to 2018 in the Beijing-Tianjin-Hebei (BTH) region, but severe PM pollution still frequently engulfs the region. The observed nitrate aerosols have not exhibited a significant decreasing trend and constituted a major fraction (about 20%) of the total PM2.5, although the surface-measured NO2 concentration has decreased by over 20%. The contributions of nitrogen oxides (NOX) emissions mitigation to the nitrate and PM2.5 concentrations and how to alleviate nitrate aerosols efficiently under the current situation still remains elusive. The WRF-Chem model simulations of a persistent and heavy PM pollution episode in January 2019 in the BTH reveal that NOX emissions mitigation does not help lower wintertime nitrate and PM2.5 concentrations under current conditions in the BTH. A 50% reduction in NOX emissions only decreases nitrate mass by 10.3% but increases PM2.5 concentrations by 3.2%, because the substantial O-3 increase induced by NOX mitigation offsets the HNO3 loss and enhances sulfate and secondary organic aerosols formation. Our results are further consolidated by the occurrence of severe PM pollution in the BTH during the COVID-19 outbreak, with a significant reduction in NO2 concentration. Mitigation of NH3 emissions constitutes the priority measure to effectively lower the nitrate and PM2.5 concentrations in the BTH under current conditions, with 35.5% and 12.7% decrease, respectively, when NH3 emissions are reduced by 50%. (c) 2021 Elsevier Ltd. All rights reserved
Mitigating NOX emissions does not help alleviate wintertime particulate pollution in Beijing-Tianjin-Hebei, China
No full textStringent mitigation measures have reduced wintertime fine particulate matter (PM2.5) concentrations by 42.2% from 2013 to 2018 in the Beijing-Tianjin-Hebei (BTH) region, but severe PM pollution still frequently engulfs the region. The observed nitrate aerosols have not exhibited a significant decreasing trend and constituted a major fraction (about 20%) of the total PM2.5, although the surface-measured NO2 concentration has decreased by over 20%. The contributions of nitrogen oxides (NOX) emissions mitigation to the nitrate and PM2.5 concentrations and how to alleviate nitrate aerosols efficiently under the current situation still remains elusive. The WRF-Chem model simulations of a persistent and heavy PM pollution episode in January 2019 in the BTH reveal that NOX emissions mitigation does not help lower wintertime nitrate and PM2.5 concentrations under current conditions in the BTH. A 50% reduction in NOX emissions only decreases nitrate mass by 10.3% but increases PM2.5 concentrations by 3.2%, because the substantial O-3 increase induced by NOX mitigation offsets the HNO3 loss and enhances sulfate and secondary organic aerosols formation. Our results are further consolidated by the occurrence of severe PM pollution in the BTH during the COVID-19 outbreak, with a significant reduction in NO2 concentration. Mitigation of NH3 emissions constitutes the priority measure to effectively lower the nitrate and PM2.5 concentrations in the BTH under current conditions, with 35.5% and 12.7% decrease, respectively, when NH3 emissions are reduced by 50%. (c) 2021 Elsevier Ltd. All rights reserved
Morpho-chemical characterization and source apportionment of potentially toxic metal(oid)s from school dust of second largest populous city of Pakistan
No full textInterior settled dust is one of the greatest threats of potentially toxic metal(oid)s (PTMs) exposure to the children, especially in the school environment. Therefore, it is more worthy of having in-depth knowledge of compositional characteristics of school dust. Forty schools were selected of Lahore city for dust sampling. The school dust was analyzed to determine the PTMs (As, Cd, Cr, Cu, Ge, Mo, Ni, Pb, Sb, Sn, Sr, V, and Zn) concentrations using ICP-MS. The morphological characteristics, PTMs speciation, and mineralogy of school dust were examined using SEM with EDS, XPS, and XRD, respectively. Moreover, the geo-accumulation index (Igeo), potential ecological risk index (PERI), and multivariate statistical analysis were employed to assess the pollution levels, ecological risk, and source identification of PTMs, respectively. The Igeo indicated a heavily-extreme pollution level of Cd (Igeo = 4.92), moderate-heavy pollution of Zn (Igeo = 3.22), and Pb (Igeo = 2.78), and slight-moderate pollution of Cr (Igeo = 1.62), and Cu (Igeo = 1.53). The ecological risk has been found extremely high for Cd and moderately high for Pb and As, while potential ecological risk found extremely high posed by cumulatively all selected PTMs. Multivariate statistical analysis showed that sources of PTMs comprise of natural processes as well as several anthropogenic processes like vehicular emissions, agricultural and industrial activities. The SEM, XRD, and XPS analyses demonstrated the presence of airborne particles and PTMs containing minerals with several toxic chemical species in school dust. This study can help to develop strategies to reduce school indoor pollution and hence to establish an eco-friendly learning environment for children
Vegetation dynamics and climate variability over the past 2000 years inferred from Son Kul marsh in the western Tianshan Mountains
No full textA pollen study was conducted on an alpine marsh sediment in the Son Kul Basin and was allowed to reconstruct changes in vegetation dynamics and climatic information in the western Tianshan Mountains during the past 2000 years. Pollen diagram reveals that regional vegetation is dominated by alpine meadow in the past 2000 years, being similar with modern vegetation components in the basin. The Artemisia/Chenopodiaceae-indicated moisture exhibits a warm-dry Roman Warm Period (RWP, similar to 0-similar to 500 AD), a cold-dry Dark Ages Cold Period (DACP, similar to 500-similar to 800 AD), a warm-wet Medieval Warm Period (MWP, similar to 800-similar to 1350 AD), a cold-dry Little Ice Age (LIA, similar to 1350-similar to 1850 AD) and a warm-dry Current Warm Period (CWP, since similar to 1850 AD). Our pollen-based moisture reconstructions are supported by other nearby moisture records. Combined with other pollen data in the western Tianshan Mountains, we found that the vegetation was relatively stable before similar to 1650-similar to 1750 AD and the anthropogenic activities obviously intensified afterwards (especially at the middle-elevation sites). Further work involving more and higher-resolution palaeovegetation records would contribute to fully understand the information on the complex links between environmental, climatic and anthropogenic changes in the western Tianshan Mountains
Oxygen vacancy-dependent photocatalytic activity of well-defined Bi2Sn2O7-x hollow nanocubes for NOx removal
No full textIntricate engineering of oxygen vacancies (OVs) to trap kinetically diffusible rarefied NO gas and to enhance the population of long-lived electrons remains a great challenge for NO removal in outdoor atmosphere. In this study, OV-engineered Bi2Sn2O7-x hollow nanocubes with distinct Sn/Bi-adjacent OVs were tightly managed and synthesized. Theoretical calculations and experimental studies revealed that not all types of OVs were beneficial for increasing the photoactivity owing to their different effects on the band structure and carrier diffusion path. Bi2Sn2O7-x with Sn-adjacent OVs could serve as adsorption sites, boosting rarefied NO enrichment and electron-hole separation. However, Bi2Sn2O7-x with Bi-adjacent OVs exhibited an opposite effect owing to increased charge recombination centers. Our findings highlight the importance of the character of OVs for efficient interface electron activation and for the removal of ambient rarefied gaseous pollutants
Changes in soil water holding capacity and water availability following vegetation restoration on the Chinese Loess Plateau
No full textChanges in land use type can lead to variations in soil water characteristics. The objective of this study was to identify the responses of soil water holding capacity (SWHC) and soil water availability (SWA) to land use type (grassland, shrubland and forestland). The soil water characteristic curve describes the relationship between gravimetric water content and soil suction. We measured the soil water characteristic parameters representing SWHC and SWA, which we derived from soil water characteristic curves, in the 0-50 cm soil layer at sites representing three land use types in the Ziwuling forest region, located in the central part of the Loess Plateau, China. Our results showed that the SWHC was higher at the woodland site than the grassland and shrubland, and there was no significant difference between the latter two sites, the trend of SWA was similar to the SWHC. From grassland to woodland, the soil physical properties in the 0-50 cm soil layer partially improved, BD was significantly higher at the grassland site than at the shrubland and woodland sites, the clay and silt contents decreased significantly from grassland to shrubland to woodland and sand content showed the opposite pattern, the soil porosity was higher in the shrubland and woodland than that in the grassland, the soil physical properties across the 0-50 cm soil layer improved. Soil texture, porosity and bulk density were the key factors affecting SWHC and SWA. The results of this study provide insight into the effects of vegetation restoration on local hydrological resources and can inform soil water management and land use planning on the Chinese Loess Plateau
Spatial variation and distribution of soil organic carbon in an urban ecosystem from high-density sampling
No full textWith acceleration of urban expansion, urban soils are increasingly becoming critical in the global carbon cycle. However, spatial variations and distributions of soil organic carbon (SOC) across urban centers are rarely investigated. Here, 1018 soil samples were collected from the upper 20 cm soil layer in Xi'an - a typical historical city under rapid urbanization in China. The aims were to: i) determine current levels and variations in SOC; ii) identify main driving factors of SOC density (SOCD); and iii) compare different interpolation methods in predicting spatial distributions of SOCD in Xi'an City study area. Results showed that the range of SOC concentration (SOCC) was 1.57-38.58 g kg(-1) (mean of 13.59 g kg(-1)) and the range of SOCD was 0.47-9.48 kg m(-2) (mean of 3.59 kg m 2). Analysis of coefficient of variation showed that there were moderate variations in SOCC (54.0%) and SOCD (49.4%) in the study area. Combined correlation analysis, principal component analysis and minimum dataset compilation showed that sand content, distance to civic center, land use type and vegetation type were closely correlated with spatial variations in SOCD. Geostatistical analysis showed that isotropic exponential model with a range of 1776 m was the best fit for SOCD semi-variogram. Spatial distribution of SOCD was further predicted using four approaches - ordinary kriging (OK), inverse distance weighting (IDW), multiple linear regression (MLG) and regression kriging (RK). The spatial prediction accuracy was ranked in order of RK > MLR > OK > IDW. However, there was relatively low interpolation accuracy for the four approaches. This was attributed to the high spatial variations in urban milieu, impacted by intense anthropogenic activities. The findings in this study added to current knowledge on global carbon cycle as influenced by urban soils, which is a critical guide to land management in urban areas
The impact of aerosol size-dependent hygroscopicity and mixing state on the cloud condensation nuclei potential over the north-east Atlantic
No full textWe present an aerosol cloud condensation nuclei (CCN) closure study over the north-east Atlantic Ocean using six approximating methods. The CCN number concentrations (N-CCN) were measured at four discrete supersaturations (SSs; 0.25 %, 0.5 %, 0.75% and 1.0 %). Concurrently, aerosol number size distribution, sub-saturation hygroscopic growth factor and bulk PM1 chemical composition were obtained at matching time resolution and after a careful data validation exercise. Method A used a constant bulk hygroscopicity parameter kappa of 0.3; method B used bulk PM1 chemical composition measured by an aerosol mass spectrometer (AMS); method C utilised a single growth factor (GF) size (165 nm) measured by a humidified tandem differential mobility analyser (HTDMA); method D utilised size-dependent GFs measured at 35, 50, 75, 110 and 165 nm; method E divided the aerosol population into three hygroscopicity modes (near-hydrophobic, more-hygroscopic and sea-salt modes), and the total CCN number in each mode was cumulatively added up; method F used the full-size-scale GF probability density function (GF-PDF) in the most complex approach. The studied periods included high-biological-activity and low-biological-activity seasons in clean marine and polluted continental air masses to represent and discuss the most contrasting aerosol populations. Overall, a good agreement was found between estimated and measured NCCN with linear regression slopes ranging from 0.64 to 1.6. The temporal variability was captured very well, with Pearson's R value ranging from 0.76 to 0.98 depending on the method and air mass type. We further compared the results of using different methods to quantify the impact of size-dependent hygroscopicity and mixing state and found that ignoring size-dependent hygroscopicity induced overestimation of N-CCN by up to 12 %, and ignoring a mixing state induced overestimation of NCCN by up to 15 %. The error induced by assuming an internal mixing in highly polluted cases was largely eliminated by dividing the full GF-PDF into three conventional hygroscopic modes, while assuming an internal mixing in clean marine aerosol did not induce significant error
Secondary Organic Aerosol Formation of Fleet Vehicle Emissions in China: Potential Seasonality of Spatial Distributions
No full textVehicle emissions are an important source of urban particular matter. To investigate the secondary organic aerosol (SOA) formation potential of real-world vehicle emissions, we exposed on-road air in Beijing to hydroxyl radicals generated in an oxidation flow reactor (OFR) under high-NOx conditions on-board a mobile laboratory and characterized SOA and their precursors with a suite of state-of-the-art instrumentation. The OFR produced 10-170 mu g m(-3) of SOA with a maximum SOA formation potential of 39-50 mu g m(-3) ppmv(-1) CO that occurred following an integrated OH exposure of (1.3-2.0) x 10(11) molecules cm(-3) s. The results indicate relatively shorter photochemical ages for maximum SOA production than previous OFR results obtained under low-NOx conditions. Such timescales represent the balance of functionalization and fragmentation, possibly resulting in different spatial distributions of SOA in different seasons as the oxidant level changes. The detected precursors may explain as much as 13% of the observed SOA with the remaining plausibly contributed by the oxidation of undetected intermediate-volatility organic compounds. Extrapolation of the results suggests an annual SOA production rate of 0.78 Tg yr(-1) from mobile gasoline sources in China, highlighting the importance of effective regulation of gaseous vehicular precursors to improve air quality in the future
Distinctive distribution and migration of global fallout plutonium isotopes in an alpine lake and its implications for sediment dating
No full textThis work investigated plutonium (Pu) isotopes in sediment cores collected from an alpine lake (Lake Heinongpo with 3779 m above sea level) in Southwestern China. Pu-240/Pu-239 atom ratios in all sediment samples showed the typical global fallout values of similar to 0.18 without any influences from other Pu contaminant sources. Pu239+240 activities with surface and subsurface maximums followed by exponential decline with sediment depth were respectively observed in the two sediment cores. The distinctive depth distributions of Pu-239,Pu-240 in the lake sediments was attributed to the very slow sediment deposition rate due to the lack of terrestrial sediment input, while the alpine snowmelt input was the primary source of Pu in the lake sediments in addition to the direct atmospheric deposition. The total Pu inventory was estimated to be 56.3 +/- 1.4 and 63.9 +/- 0.8 Bq/m(2) respectively in the two sediment cores. The generally higher Pu inventory in the Lake Heinongpo compared with other reported lakes in similar latitude should be mainly attributed to their different Pu input passages. The advection-diffusion equation was further applied to evaluate the downward migration of Pu isotopes in the sediment cores and predict the future evolution of Pu distribution in the sediment cores. The fitted results indicated that the diffusion effect controlled the downward migration of Pu in the sediments, but this diffusive migration will not prevent the peak of global fallout Pu in undisturbed sediment cores from being a valuable time marker for sediment dating. (C) 2021 Elsevier Ltd. All rights reserved