Chemical Source Profiles and Toxicity Assessment of Urban Fugitive Dust PM2.5 in Guanzhong Plain, China

Urban fugitive dust is a significant contributor to atmospheric PM2.5 and a potential risk to humans. In 2019, both road dust and construction dust were collected from four cities, including Xi'an, Xianyang, Baoji, and Tongchuan, in Guanzhong Plain, China. Elements, water-soluble ions, and carbonaceous fractions were determined to establish the chemical source profile. High enrichment degrees of Se, Sc, Cl, and Zn in both road dust and construction dust indicated that the industrial system and energy consumption influenced Guanzhong Plain strongly. According to the coefficient of divergence, the two datasets within Xianyang and Tongchuan were similar. Combined with the chemical profile, road dust was affected by more stationary emission sources than construction dust in Xi'an, while biomass burning and vehicle exhaust contributed more to road dust than construction dust in Baoji. Moreover, the health risk of heavy metal was assessed, and corresponding influencing factors were identified. Road dust in all cities showed a non-negligible non-carcinogenic risk for children. Ingestion and inhalation were the main exposure pathways to which As and Co contributed the most, respectively. The land-use regression model revealed that the first-class road in a 100 m radius impacted all high-risk level metals, and the commercial building material and enterprises weakly influenced Co and Pb, respectively.

[Characteristics and source of soil condensation water in Guanzhong Plain, China]

We determined the quantity and source of soil water condensation versus atmospheric vapor condensation in Guanzhong Plain and explored their role in water balance, using three different types of hand-made micro-lysimeters (open-ends, top-seal, and bottom-seal designs). Field monitoring of the vapor condensation process was carried out from late September to late October in 2018 and from March to May in 2019 using the weighing method. Results showed that during the monitoring period, condensation occurred every day without rainfall event. The maximum daily condensation for the open-ends, top-seal and bottom-seal designs were 0.38, 0.27 and 0.16 mm, respectively, indicating that vapor flow in soil pores was the main source of soil water condensation, and that the measurement using the open-ended micro-lysimeter could faithfully reflect the amount of condensation in Guanzhong Plain. During the monitoring period, total soil water condensation reached 14.94 mm, accounting for 12.8% of the precipitation in the same period (116.4 mm), and the ratio of atmospheric vapor condensation to soil vapor condensation was 0.59:1.

Variation and multi-time series prediction of total hardness in groundwater of the Guanzhong Plain (China) using grey Markov model

Total hardness (TH) is an important index representing the water suitability for domestic purpose. TH is represented mainly by Ca²⁺ and Mg²⁺ which are essential elements for human bone development. Between 2000 and 2015, the TH values of groundwater in major cities of the Guanzhong Plain varied significantly. The study was carried out to investigate TH variation over 16 years and to examine how effective the grey Markov model was in predicting TH concentrations in time series datasets. The hydrochemical parameters determining TH concentration and their origins were investigated using statistical analysis and geochemical models. The grey Markov model, which is effective in short time series prediction, was used to forecast the multi-time series of TH. The findings demonstrated a prevalence of HCO₃^- and SO₄^2- in the groundwater types combined with calcite precipitation, gypsum, and dolomite dissolution that increased the concentration of Ca²⁺, Mg²⁺, and HCO₃^-, influencing TH variation. The predicted TH values of the eight monitoring wells for the year 2016 were 1213.66, 124.30, 203.66, 103.01, 349.56, 251.23, 453.31, and 471.81 mg/L, respectively. Datasets with low TH variation were more accurately predicted than datasets with high TH variation. This was especially observed on sample B557 where TH concentration in 2010 was 400.33 mg/L and suddenly dropped to 90.1, 82.6, 85.1, 87.6, and 75.1 mg/L in 2011, 2012, 2013, 2014, and 2015, respectively. The study also shows that the Markov chain model can optimize the GM(1,1) model and improve the prediction accuracy significantly. All samples in Weinan City and one sample in Xi'an City showed a significant decrease in TH concentration. Except one sample in Xi'an City, TH concentrations tended to rise in the other cities (Baoji, Xianyang) of the Guanzhong Plain. This study verified the reliability of the grey Markov model in terms of forecasting time series datasets with high variability, and the results can be referential to similar studies in the world.

[Effects of Stalk Incorporation on Soil Carbon Sequestration, Nitrous Oxide Emissions, and Global Warming Potential of a Winter Wheat-Summer Maize Field in Guanzhong Plain]

The net greenhouse gas emissions from upland soils, as indicated by global warming potential (GWP), mainly depend on the soil carbon sequestration and nitrous oxide (N₂O) emissions. The annual changes in surface (0-20 cm) soil organic carbon (SOC) content from 2010 to 2017 and the N₂O emissions from 2014 to 2017 were measured within a long-term fertilization experiment. The objective was to quantify the effect of stalk incorporation on the soil carbon sequestration, annual N₂O emissions, and GWP of a winter wheat-summer maize field in the Guanzhong Plain. The field experiment included three treatments:conventional fertilization (CF), conventional fertilization plus maize stalks (CFS), and an unfertilized control (CK). The CF and CFS treatments received the same amount of urea per year, with nitrogen (N) input at 165 kg·hm^-2 and 188 kg·hm^-2 in the winter wheat season and summer maize season, respectively. The CF treatment retained the stubbles (about 10 cm above ground) when harvesting the winter wheat and summer maize crops. The CFS treatment retained the same wheat stubbles and all maize stalks (containing approximately 40 kg·hm^-2 of N). The CK treatment was unfertilized throughout the year, with the stubble management the same as that in the CF treatment. The results showed that the CK treatment displayed few changes in SOC content and low N₂O emissions, with GWP varying from 0.04 to 0.11 t·(hm²·a)^-1. The SOC contents in the CF and CFS treatments increased linearly with the fertilization years (P<0.001), and their SOC sequestration rates were 0.69 t·(hm²·a)^-1 and 0.97 t·(hm²·a)^-1, respectively. The N₂O emissions from the CF and CFS treatments varied from 1.65 to 5.36 kg·(hm²·a)^-1 and from 3.08 to 7.73 kg·(hm²·a)^-1, respectively. The annual N₂O emissions from the CFS treatment were 43%-94% higher than those from the CF treatment, whereas the difference was only significant between 2015 and 2016 (P<0.05). The GWP of the CF and CFS treatments varied from -1.95 to -0.28 t·(hm²·a)^-1 and from -2.59 to -0.35 t·(hm²·a)^-1, respectively. The cumulative GWP of the CFS treatment was 42% lower than that of the CF treatment between 2014 and 2017. In summary, the studied winter wheat-summer maize field acted as a sink of greenhouse gases under the conventional fertilization regime. The stalk incorporation further favored greenhouse gas mitigation despite the trade-offs between SOC sequestration and N₂O emissions.

[Analysis of Hydrogen and Oxygen Stable Isotope Characteristics and Vapor Sources of Precipitation in the Guanzhong Plain]

To improve the understanding of hydrogen and oxygen stable isotope characteristics and vapor sources in the Guanzhong Plain, we collected 98 precipitation samples and corresponding meteorological data between 2015 and 2018 in Yangling, Shanxi Province, which is located in the central area of the Guanzhong Plain. The composition characteristics of the local hydrogen and oxygen stable isotopes of precipitation (δ²H, δ¹⁸O, and δ¹⁷O) and their environmental controls were analyzed, and the local meteoric water line (LMWL) and the meteoric water line of the triple oxygen isotopes were established. Three indicators (δ¹⁸O, d-excess, and ¹⁷O-excess) were used to explore the possible vapor sources of local precipitation and to quantify the contributions of ocean-source and inland-source water vapor to the precipitation. The results showed that there were obvious seasonal changes in the hydrogen and oxygen stable isotopes of precipitation in the Yangling area:water isotopes were depleted in the wet season (May to October) and enriched in the dry season (November to April of the next year). Both the slope (7.7) and intercept (9.1) of the LMWL were lower than those of the global meteoric water line (GMWL), indicating that the annual precipitation in the research area experienced variable degrees of secondary evaporation under cloud cover. The slope of the meteoric water line of the triple oxygen isotopes is 0.528, which is between that of seawater equilibrium fractionation (0.529) and water vapor diffusion into dry air (0.518), consistent with the fact that the Guanzhong area is located on the migration path of marine air mass to inland arid regions. Comprehensive analysis of δ¹⁸O, d-excess, and ¹⁷O-excess confirmed that the precipitation in the study area is jointly contributed to by the warm and humid air mass from the southeast monsoon and the dry and cold air mass from the westerly wind. Of these, approximately 55%-79% of the precipitation water vapor comes from the ocean, mainly in June to August, and about 21%-45% of the water vapor comes from inland and local evaporation, mainly from October to April. The water vapor sources of precipitation in May and September are complex and may intermittently originate from ocean and inland water vapor.

[Effect of Long-term Dairy Manure Amendment on N2O and NO Emissions from Summer Maize-Winter Wheat Cropping Systems]

Annual nitrous oxide (N₂O) and nitric oxide (NO) emissions were measured within a 27 year fertilization experiment in Guanzhong Plain. Gas samples were collected using static chambers from June 2017 to June 2018. The primary objectives of this study were to quantify the variations in N₂O and NO emissions and evaluate the effect of manure amendment on gas losses. Three treatments were set up in the field using a completely random block design. The control treatment (CK) remained unfertilized throughout the year. The synthetic fertilizers (NPK) and NPK plus dairy manure (NPKM) treatments received an annual nitrogen (N) input at a rate of 353 kg·hm^-2. In the summer maize season, the NPK and NPKM treatments received urea as a N source at 188 kg·hm^-2. In the winter wheat season, the NPK treatments received urea at 165 kg·hm^-2. The NPKM treatment received the same amount of N as the NPK treatment but with 30% from urea and 70% from dairy manure. The results showed that N₂O and NO emissions from the CK treatment were consistently low during the experimental period. Large emission peaks were captured in the NPK and NPKM treatments, mostly responding to fertilizer application and irrigation. The largest N₂O and NO peaks were up to 103.0 g·(hm²·d)^-1 and 71.0 g·(hm²·d)^-1, respectively, and both occurred in the NPKM treatment during the summer maize season. The NO/N₂O ratio was negatively related to soil water-filled pore space (P<0.01) at soil temperatures above 20℃ for the NPK and NPKM treatments, indicating the regulatory effect of soil temperature and water content on gas fluxes. Annual N₂O emissions from the CK, NPK, and NPKM treatments were 0.21 kg·hm^-2, 2.32 kg·hm^-2, and 2.15 kg·hm^-2, respectively, with a non-significant difference between the NPK and NPKM treatments (P=0.74). Annual NO emissions from the CK, NPK, and NPKM treatments were 0.23 kg·hm^-2, 0.80 kg·hm^-2, and 1.46 kg·hm^-2, respectively, with a significant difference between the NPK and NPKM treatments (P<0.05). We concluded that long-term dairy manure amendment did not influence N₂O emissions but increased NO emissions.

Identification of sources of metal in the agricultural soils of the Guanzhong Plain, northwest China

A comprehensive survey was conducted to assess the possible sources and distribution of metals in the agricultural soils of the Guanzhong Plain in northwest China. In total, 227 samples of agricultural soil were collected to determine the content of Pb, Cr, Co, V, Ni, Zn, Cu, As, and Mn by X-ray fluorescence spectrometry. The mean concentrations of metals were 26.2 ± 10.8 mg kg^--1 , 71.5 ± 16.8 mg kg^-1 , 12.7 ± 1.81 mg kg^-1 , 85.1 ± 7.86 mg kg^-1 , 30.5 ± 6.17 mg kg^-1 , 71.1 ± 14.1 mg kg^-1 , 25.2 ± 5.58 mg kg^-1 , 12.5 ± 1.94 mg kg^-1 , and 635.4 ± 84.7 mg kg^-1 for Pb, Cr, Co, V, Ni, Zn, Cu, As, and Mn, respectively-slightly higher than the regional background values. Multivariate analysis was used to identify the metal sources, and it was found that Ni and Cr in the agricultural soils were mainly derived from lithological materials, and Pb, Zn, and Cu were mainly from traffic emissions; however, Zn and Cu also originated from mineral fertilizers or pesticides. The other metals originated from industrial emissions. The Nemerow index coupled with geographic information system technology was applied to assess the degree and spatial distribution of metal contamination; the soils studied were classified as slightly polluted, and the most contaminated regions were concentrated in the area surrounding Xi'an city, as well as areas in the southeast and north of the Guanzhong Plain. Environ Toxicol Chem 2017;36:1510-1516. © 2016 SETAC.