Pollutants, which are usually transported from urban cities to remote glacier basins, and aerosol impurities affect the earth's temperature and climate by altering the radiative properties of the atmosphere. This work focused on the physicochemical properties of atmospheric pollutants across the urban and remote background sites in northwest China. Information on individual particles was obtained using transmission electron microscopy (TEM) and energy dispersive X-ray spectrometry (EDX). Particle size and age-dependent mixing structures of individual particles in clean and polluted air were investigated. Aerosols were classified into eight components: mineral dust, black carbon (soot)/fly ash, sulfates, nitrates, NaCl salt, ammonium, organic matter, and metals. Marked spatial and seasonal changes in individual particle components were observed in the study area. Aerosol particles were generally found to be in the mixing state. For example, salt-coated particles in summer accounted for 31.2–44.8% of the total particles in urban sites and 37.5–74.5% of the total particles in background sites, while in winter, almost all urban sites comprised >50%, which implies a significant effect on the radiative forcing in the study area. We found that in PM₂.₅ section, the internally mixed black carbon/organic matter particles clearly increased with diameter. Moreover, urban cities were characterized by atmospheric particles sourced from anthropogenic activities, whereas background locations exhibited much lower aerosol concentrations and increased particle density, originating from natural crustal sources (e.g., mineral dust and NaCl salt), which, together with air mass trajectory analysis, indicates a potential spatial transport process and routes of atmospheric transport from urban cities to background locations. Thus, this work is of importance in evaluating atmospheric conditions in northwest China and northeast Tibetan Plateau regions, to discover the transport processes and facilitate improvements in climatic patterns concerning atmospheric impurities.

The occurrence and spatial distribution of selected pesticides were investigated along a 200-km reach of the St. Lawrence River (SLR) and tributaries in Quebec, Canada. Surface water samples (n = 68) were collected in the summer 2017 and analyzed for glyphosate, atrazine (ATZ), 8 systemic insecticides (acetamiprid, clothianidin, dinotefuran, fipronil, imidacloprid, nitenpyram, thiacloprid, and thiamethoxam) and some metabolites. Overall, 99% of the surface water samples were positive to at least one of the targeted pesticides. The most recurrent compounds were glyphosate (detection frequency: 84%), ATZ (82%), thiamethoxam (59%), desethylatrazine (DEA: 47%), and clothianidin (46%). Glyphosate displayed variable levels (4–3,000 ng L−1), with higher concentrations in south tributaries (e.g., Nicolet and Yamaska). In positive samples, the sum of ATZ and DEA varied between 5 and 860 ng L−1, and the sum of 6 priority neonicotinoids between 1.5 and 115 ng L−1. From Repentigny to the Sorel Islands, the spatial distribution of pesticides within the St. Lawrence River was governed by the different upstream sources (i.e., Great Lakes vs. Ottawa River) due to the limited mixing of the different water masses. Cross-sectional patterns revealed higher concentrations of glyphosate and neonicotinoids in the north portions of transects, while the middle and south portions showed higher levels of atrazine. In Lake St. Pierre and further downstream, cross-sections revealed higher levels of the targeted pesticides near the southern portions of the SLR. This may be due to the higher contributions from south shore tributaries impacted by major agricultural areas, compared to north shore tributaries with forest land and less cropland use. Surface water samples were compliant with guidelines for the protection of aquatic life (chronic effects) for glyphosate and atrazine. However, 31% of the samples were found to surpass the guideline value of 8.3 ng L−1 for the sum of six priority neonicotinoids.

Biochar as a porous carbon material could be used for improving soil physical and chemical properties, while insufficient attention has been paid to potential risks induced by infiltration of heavy metals in the runoff water flowing through biochar-amended soil. Four different soil-biochar matrices with same volumes were constructed including soil alone (M1), biochar alone (M2), soil-biochar layering (M3) and soil-biochar mixing (M4). Leaching experiments were conducted with Pb, Cu, and Zn contaminated runoff water. Results showed that biochar amendment greatly improved the water permeation, and the infiltration rates in M2, M3, and M4 were 2.85–23.0 mm min⁻¹, being much higher than those in M1 (1.33–4.05 mm min⁻¹), though the rates decreased as the leaching volumes increased. However, biochar induced more Pb, Cu, and Zn infiltrated through soil-biochar matrix. After 350-L leaching, M1 retained about 95% Pb, 90% Cu, and 36% Zn, while M2 only retained 4.80% Pb, 17.4% Cu, and 4.01% Zn; about 30% Pb, 80% Cu, and 15% Zn were retained in M3 and M4. Notably, Zn was trapped first and then re-leached into the filtrate, which resulted in a much higher effluent Zn than the influent Zn at the later stage. However, the unit weight of biochar showed a higher capacity for retaining heavy metals compared to per unit of soil. Under the dynamic water flow, all benefits and disadvantages induced by biochar were weakened with its physical disintegration. Biochar as soil amendment can enhance plant growth via ameliorating soil structure, while it would pose risks to environment because of large penetration of heavy metals. If biochar was compacted to form a denser physical structure, perhaps more heavy metals could be retained.

Hydrogeochemistry and isotope hydrology were carried out to investigate the spatial distribution of fluoride (F−) and the mechanisms responsible for its enrichment in the western region of the Ordos basin, northwestern China. Sixty-two groundwater samples from the unconfined aquifer and fifty-six from confined aquifer were collected during the pre-monsoon (June 2016). Over 77% of groundwater samples from the unconfined aquifer (F− concentration up to 13.30 mg/L) and approximately 66% from confined aquifer (with a maximum F− concentration of 3.90 mg/L) exhibit F− concentrations higher than the Chinese safe drinking limit (1.0 mg/L). High-F− groundwater presents a distinctive hydrochemical characteristic: a high pH value and HCO3− concentration with Ca-poor and Na-rich. Mineral dissolution (e.g., feldspar, calcite, dolomite, fluorite), cation exchange and evaporation in the aquifers predominate the formation of groundwater chemistry, which are also important for F− enrichment in groundwater. Mixing with unconfined groundwater is a significant mechanism resulting in the occurrence of high-F− groundwater in confined aquifer. These findings indicate that physicochemical processes play crucial roles in driving F− enrichment and that may be useful for studying F− occurrence in groundwater in arid and semi-arid areas.

Apportioning sources of environmental pollutants is key to controlling pollution. In this study, the sources of heavy metals to 234 agricultural soils from the Jianghan Plain (JHP) (∼22454 km2) in central China were discriminated between using Cd and Pb isotope compositions and multivariate statistical analyses. Concentrations of some metals in JHP soils (0.48 ± 0.2, 48.2 ± 15.9, 0.12 ± 0.23, 48.8 ± 16.4, 36.5 ± 9.8, and 96.8 ± 42.2 mg kg−1 for Cd, Cu, Hg, Ni, Pb, and Zn, respectively) were higher than background concentrations in Chinese soil. The Cd isotope compositions for the JHP soils (δ114/110Cd values −0.76‰ to −0.25‰) were similar to Cd isotope compositions found for smelter dust and incinerator fly ash, indicating Cd was supplied to the JHP soils by ore smelting and/or refining processes. The Pb isotope compositions for the JHP soils (206Pb/207Pb 1.182–1.195 and 208Pb/206Pb 2.078–2.124) were between the Pb isotope compositions found for Chinese coal and natural sources, which a binary isotope mixing model indicated contributed 52% and 48%, respectively, of the Pb in JHP soils. Cluster analysis and positive matrix factorization indicated that the sources of heavy metals in JHP soils may consist of smelting and/or refining activities, coal combustion, agricultural activities, and natural sources (including Han River sediment and soil parent materials). The isotope fingerprints and multivariate statistical analyses together indicated that coal combustion and smelting and/or refining activities were the main anthropogenic sources of heavy metals polluting JHP soils.

Stable isotopes ratios (‰) of Hydrogen (δ2H) and Oxygen (δ1⁸O) were used to trace the groundwater recharge mechanism and geochemistry of arsenic (As) contamination in groundwater from four selected sites (Larkana, Naudero, Ghari Khuda Buksh and Dokri) of Larkana district. The stable isotope values of δ2H and δ1⁸O range from 70.78‰ to −56.01‰ and from −10.92‰ to −7.35‰, relative to Vienna Standard for Mean Ocean Water (VSMOW) respectively, in all groundwater samples, thus indicating the recharge source of groundwater from high-salinity older water. The concentrations of As in all groundwater samples were ranged from 2 μg/L to 318 μg/L, with 67% of samples exhibited As levels exceeding than that of World Health Organization (WHO) permissible limit 10 μg/L and 42% of samples expressed the As level exceeding than that of the National Environmental Quality Standard (NEQS) 50 μg/L. The leaching and vertical mixing with return irrigation water are probably the main processes controlling the enrichment of As in groundwater of Larkana, Naudero, Ghari Khuda Buksh and Dokri. The weathering of minerals mostly controlled the overall groundwater chemistry; rock-water interactions and silicate weathering generated yielded solutions that were saturated in calcite and dolomite in two areas while halite dissolution is prominent with high As area.

The imprints of fireworks displays on the adjacent water body were investigated from the perspective of cogeneration of black carbon, metals and perchlorate (ClO₄⁻). In particular, the mixing and dissipation of ClO₄⁻ were studied at Oak Lake, Lincoln, Nebraska, following fireworks displays in 2015 and 2016. Following the display, ClO₄⁻ concentration in the water increased up to 4.3 μg/L and 4.0 μg/L in 2015 and 2016, respectively. A first-order model generally provided a good fit to the measured perchlorate concentrations from which the rate of dissipation was estimated as 0.07 d⁻¹ in 2015 and 0.43 d⁻¹ in 2016. SEM images show imprints of soot and metal particles in aerosol samples. EDS analysis of the lake sediment confirmed the presence of Si, K, Ca, Zn and Ba, most of which are components of fireworks. The δ¹³C range of −7.55‰ to −9.19‰ in the lake water system closely resembles fire-generated carbon. Cogeneration of black carbon and metal with perchlorate was established, indicating that ClO₄⁻ is an excellent marker of fireworks or a burning event over all other analyzed parameters. Future microcosmic, aggregation and column-based transport studies on black carbon in the presence of perchlorate and metals under different environmental conditions will help in developing transport and fate models for perchlorate and black carbon particles.

This study implements a two-box model coupled with ultrafine particle (UFP) multicomponent microphysics for a compartmentalised street canyon. Canyon compartmentalisation can be described parsimoniously by three parameters relating to the features of the canyon and the atmospheric state outside the canyon, i.e. the heterogeneity coefficient, the vortex-to-vortex exchange velocity, and the box height ratio. The quasi-steady solutions for the two compartments represent a balance among emissions, microphysical aerosol dynamics (i.e. evaporation/condensation of semi-volatiles, SVOCs), and exchange processes, none of which is negligible. This coupled two-box model can capture significant contrasts in UFP number concentrations and a measure of the volatility of the multi-SVOC-particles in the lower and upper canyon. Modelled ground-level UFP number concentrations vary across nucleation, Aitken, and accumulation particle modes as well-defined monotonic functions of canyon compartmentalisation parameters. Compared with the two-box model, a classic one-box model (without canyon compartmentalisation) leads to underestimation of UFP number concentrations by several tens of percent typically. By quantifying the effects of canyon compartmentalisation, this study provides a framework for understanding how canyon geometry and the presence of street trees, street furniture, and architectural features interact with the large-scale atmospheric flow to determine ground-level pollutant concentrations.

A systematic field measurement was conducted at an island site (Wanshan Island, WSI) over the South China Sea (SCS) in autumn 2013. It was observed that mixing ratios of O₃ and its precursors (such as volatile organic compounds (VOCs), nitrogen oxides (NOₓ = NO + NO₂) and carbon monoxide (CO)) showed significant differences on non-episode days and episode days. Additional knowledge was gained when a photochemical box model incorporating the Master Chemical Mechanism (PBM-MCM) was applied to further investigate the differences/similarities of O₃ photochemistry between non-episode and episode days, in terms of O₃-precursor relationship, atmospheric photochemical reactivity and O₃ production. The simulation results revealed that, from non-O₃ episode days to episode days, 1) O₃ production changed from both VOC and NOₓ-limited (transition regime) to VOC-limited; 2) OH radicals increased and photochemical reaction cycling processes accelerated; and 3) both O₃ production and destruction rates increased significantly, resulting in an elevated net O₃ production over the SCS. The findings indicate the complexity of O₃ pollution over the SCS.

The concentration and spatial distribution of microplastics in the Bay of Brest (Brittany, France) was investigated in two surveys. Surface water and sediment were sampled at nine locations in areas characterized by contrasting anthropic pressures, riverine influences or water mixing. Microplastics were categorized by their polymer type and size class. Microplastic contamination in surface water and sediment was dominated by polyethylene fragments (PE, 53–67%) followed by polypropylene (PP, 16–30%) and polystyrene (PS, 16–17%) microparticles. The presence of buoyant microplastics (PE, PP and PS) in sediment suggests the existence of physical and/or biological processes leading to vertical transfer of lightweight microplastics in the bay. In sediment (upper 5 cm), the percentage of particles identified by Raman micro-spectroscopy was lower (41%) than in surface water (79%) and may explain the apparent low concentration observed in this matrix (0.97 ± 2.08 MP kg−1 dry sediment). Mean microplastic concentration was 0.24 ± 0.35 MP m−3 in surface water. We suggest that the observed spatial MP distribution is related to proximity to urbanized areas and to hydrodynamics in the bay. A particle dispersal model was used to study the influence of hydrodynamics on surface microplastic distribution. The outputs of the model showed the presence of a transitional convergence zone in the centre of the bay during flood tide, where floating debris coming from the northern and southern parts of the bay tends to accumulate before being expelled from the bay. Further modelling work and observations integrating (i) the complex vertical motion of microplastics, and (ii) their point sources is required to better understand the fate of microplastics in such a complex coastal ecosystem.