Fine particulate matter (PM₂.₅) has attracted extensive attention because of its baneful influence on human health and the environment. However, the sparse distribution of PM₂.₅ measuring stations limits its application to public utility and scientific research, which can be remedied by satellite observations. Therefore, we developed a Geo-intelligent long short-term network (Geoi-LSTM) to estimate hourly ground-level PM₂.₅ concentrations in 2017 in Wuhan Urban Agglomeration (WUA). We conducted contrast experiments to verify the effectiveness of our model and explored the optimal modeling strategy. It turned out that Geoi-LSTM with TOA reflectance, meteorological conditions, and NDVI as inputs performs best. The station-based cross-validation R², root mean squared error and mean absolute error are 0.82, 15.44 μg/m³, 10.63 μg/m³, respectively. Based on model results, we revealed spatiotemporal characteristics of PM₂.₅ in WUA. Generally speaking, during the day, PM₂.₅ concentration remained stable at a relatively high level in the morning and decreased continuously in the afternoon. While during the year, PM₂.₅ concentrations were highest in winter, lowest in summer, and in-between in spring and autumn. Combined with meteorological conditions, we further analyzed the whole process of a PM₂.₅ pollution event. Finally, we discussed the loss in removing clouds-covered pixels and compared our model with several popular models. Overall, our results can reflect hourly PM₂.₅ concentrations seamlessly and accurately with a spatial resolution of 5 km, which benefits PM₂.₅ exposure evaluations and policy regulations.

In general, tire tread rubber compounds contain oleamide for improvement of manufacturing processibility, mold release characterization, and abrasion resistance. Tire tread wear particles (TWPs) are one of major contributors to microplastic emissions. In this study, a novel analytical method for quantification of TWP in microparticles produced on the road (road dust, MPRs) was developed by employing oleamide as a new marker. MPRs were collected at bus stops in autumn, winter, and summer seasons. MPRs of 38–63, 63–106, 106–212, and 212–500 μm obtained by size separation were employed for the analysis. Rubber components for bus and passenger car tire tread compounds were identified using pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). Oleamide was extracted from the MPRs with acetone and was identified using GC/MS. The oleamide concentration was analyzed using GC equipped with flame ionization detector (FID). The TWP contents of the MPRs were determined using the oleamide concentrations and the reference compound formulations. In order to reduce the sampling errors, each experiment was carried out five times and the results were averaged. The TWP contents of the MPRs were 1.4–4.7 wt% and were different according to the sampling seasons and places. The TWP contents were increased by increasing the traffic volume and the temperature.

140 contaminants belonging to various classes (organochlorine and organophosphorus pesticides, pyrethroid insecticides, carbamates, fungicides, acaricides, herbicides, synergists, insect growth regulators, polychlorobiphenyls, polycyclic aromatic hydrocarbons) were simultaneously analysed by GC-MS/MS in marine sediments, aquatic plant leaves and fish tissues samples. A total of 260 samples from five stations along the coast of Tunisia were evaluated. The results highlight that only 28 residues (12 polychlorobiphenyls, 8 organochlorine pesticides, 7 polycyclic aromatic hydrocarbons and triphenyl phosphate) were detected at levels higher than relative LOQ values. The amounts in sediment samples were compared with Sediment Quality Guidelines (SQGs) showing that the values are acceptable and no toxic effect is expected on aquatic organisms. A little variation of contaminant residues in sediment samples among coastal stations was recorded. Namely, with respect to almost all polychlorobiphenyls and organochlorine pesticides, higher values were recorder in summer. With respect to almost all polycyclic aromatic hydrocarbons, higher values were recorder in autumn. Aquatic plant leaves showed a residue accumulation higher than that of other compartments of marine system. The data about fish samples (Sparus aurata and Sarpa salpa, the two most frequently caught fish species at five sites on the central coast of Tunisia) do not pose direct hazard to human health because values were lower than protection limits.

Controlling ammonia (NH₃) emissions has been proposed as a strategy to mitigate haze pollution. To explore the role of NH₃ in haze pollution in Sichuan Basin, where agricultural activities are intense, hourly in situ data of NH₃, as well as nitric acid and secondary inorganic aerosols (SIAs) were gathered in Chengdu from April 2017 to March 2018. We found that NH₃ had an annual mean concentration of 9.7 ± 3.5 (mean ± standard deviation) μg m⁻³, and exhibited seasonal variations (spring > summer > autumn and winter) due to changes in emission sources and meteorological conditions (particularly temperature). Chengdu's atmosphere is generally NH₃-sufficient, especially in the warm seasons, implying that the formation of SIAs is more sensitive to the availability of nitric acid. However, an NH₃ “sufficient-to-deficient” transition was found to occur during winter pollution periods, and the frequency of NH₃ deficiency increased with the aggravation of pollution. Under NH₃-deficient conditions, the nitrogen oxidation ratio increased linearly with the increase in free NH₃, implying that NH₃ contributes appreciably to the formation of nitrate and thus to high PM₂.₅ loadings. No relationships of NH₃ with fossil fuel combustion–related pollutants were found. The NH₃ emissions from farmland and livestock waste in the suburbs of Chengdu and regional transport from west of Chengdu probably contribute to the occurrence of high PM₂.₅ loading in winter and spring, respectively. These results suggest that to achieve effective mitigation of PM₂.₅ in Chengdu, local and regional emission control of NH₃ and NOx synergistically would be effective.

General population are concurrently and extensively exposed to many volatile organic compounds (VOCs), including some Group 1 human carcinogens, such as 1,3-butadiene. However, only a few studies assessed internal exposure levels of VOCs; particularly, very limited studies have examined associations between the urinary concentrations of multiple VOC metabolites (mVOCs) and oxidative stress biomarkers (OSBs) among the general population. In this study, 21 mVOCs and three OSBs including 8-hydroxy-2′-deoxyguanosine (8-OHdG; for DNA), 8-hydroxyguanosine (8-OHG; for RNA), and 4-hydroxy nonenal mercapturic acid (HNEMA; for lipid) were measured in 406 urine samples collected from 128 healthy adults during autumn and winter of 2018 in Wuhan, central China, including repeated samples taken in 3 d from 75 volunteers. Inter-day reproducibility for most mVOCs was good to excellent; urinary concentrations of mVOCs in winter were generally higher than those in autumn. Risk assessment was conducted by calculating hazard quotients for the parent compounds, and the results suggested that acrolein, 1,3-butadiene, and cyanide should be considered as high-priority hazardous ones for management. After false-discovery adjustment, 16 of the studied mVOCs were positively associated with 8-OHdG and 8-OHG (β values ranged from 0.04 to 0.48), and four mVOCs were positively associated with HNEMA (β values ranged from 0.21 to 0.78). Weighted quantile sum regression analyses were used to assess associations of mVOC mixture and OSBs, and we found significantly positive associations between the mixture index and OSBs, among which the strongest mVOC contributors for the associations were 2-methylhippuric acid for both DNA (20%) and RNA (17%) oxidative damage, and trans,trans-muconic acid (50%) for lipid peroxidation. This study firstly reported good to excellent short-term reproducibility, seasonal difference in autumn and winter, and possible health risk in urinary concentrations of multiple mVOCs among the general population.

In this study, we integrated a remote-sensing fire product (MOD14A1) and land-use product (MCD12Q1) to extract the number of crop-residue burning (CRB) spots and the fire radiative power (FRP) in China from 2001 to 2018. Moreover, we conducted three trend analyses and two geographic distribution analyses to quantify the interannual variations and summarize the spatial characteristics of CRB on grid (0.25° × 0.25°) and regional scales. The results indicated that CRB presents distinctive seasonal patterns with each sub-region. All trend analyses suggested that the annual number of CRB spots in China increased significantly from 2001 to 2018; the linear trend reached 2615 spots/year, the Theil-Sen slope was slightly lower at 2557 spots/year, and the Mann-Kendal τ was 0.75. By dividing the study period into two sub-periods, we found that the five sub-regions presented different trends in the first and second sub-periods; e.g., the Theil-Sen slope of eastern China in the first sub-period (2001–2009) was 1021 spots/year but was −1599 spots/year in the second period (2010–2018). This suggests that summer CRB has been effectively mitigated in eastern China since 2010. Further, the average FRP of CRB spots presented a decreasing trend from 27.5 MW/spot in 2001 to only 15.8 MW/spot in 2018; this may be attributable to more scattered CRB rather than aggregated CRB. Collectively, the fire spots, FRP, and average FRP indicated that spring, summer, and autumn CRB had dropped dramatically over previous levels by 2018 due to strict mitigation measures by local governments.

The distribution of freshwater and marine microplastics (MPs) varies due to the difference in fresh and seawater densities and MP sources. This study aims to investigate the abundance of MPs and their possible sources in surface waters of different ecosystems, such as sea, lagoon, and lake. We classified MPs in terms of their color and type and established the relationship between the MPs in surface waters with different characteristics. The mean MP abundance (33 particles L⁻¹) detected herein was higher than that in the previously conducted studies. Fragment particles (37.95%) were determined to be the dominant MP type, and the predominant MP color was blue (75.28%). As for the seasonal MP distribution, its highest content (48.03 particles L⁻¹) was observed in autumn, unlike that reported by other studies. The findings of this study reveal the effects of wastewater treatment plant (WWTP) discharge and current flow on the MP distribution in the study area. This study aims to provide representative data on the MP abundance and distribution, as well as MP-affecting parameters for similar aquatic areas in other parts of the world.

In recent years, implementation of aggressive and strict clean air policies has resulted in significant decline in observed PM₂.₅ concentration in the Beijing–Tianjin–Hebei (BTH) region and its surrounding areas (i.e., the “2 + 26” region). To eliminate the effects of interannual and seasonal meteorological variation, and to evaluate the effectiveness of emission abatement policies, we applied a boosted regression tree model to remove confounding meteorological factors. Results showed that the annual average PM2.5 concentration normalized by meteorology for the “2 + 26” region declined by 38% during 2014–2019 (i.e., from 96 to 60 μg/m³); however, the BTH region exhibited the most remarkable decrease in PM₂.₅ concentration (i.e., a 60% reduction). Certain seasonal trend in normalized PM₂.₅ level remained for four target subregions owing to the effects of anthropogenic emissions in autumn and winter. Although strong interannual variations of meteorological conditions were unfavorable for pollutant dispersion during the heating seasons of 2016–2018, the aggressive abatement policies were estimated to have contributed to reductions in normalized PM₂.₅ concentration of 19%, 10%, 19%, and 17% in the BTH, Henan, Shandong, and Shanxi subregions, respectively. Our study eliminated the meteorological contribution to concentration variation and confirmed the effectiveness of the implemented clean air policies.

This paper presents the results of the study on columnar aerosol optical and physical properties and radiative effects directly observed over Dushanbe, the capital city of Tajikistan, a NASA AERONET site (equipped with a CIMEL sunphotometer) in Central Asia. The average aerosol optical depth (AOD) and Ångström exponent (AE) during the observation period from July 2010 to April 2018 were found to be 0.28 ± 0.20 and 0.82 ± 0.40, respectively. The highest seasonal AOD (0.32 ± 0.24), accompanied by the lowest average AE (0.61 ± 0.25) and fine-mode fraction in AOD (0.39), was observed during summer due to the influence of coarse particles like dust from arid regions. Fine particles were found in significant amounts during winter. The ‘mixed aerosol’ was identified as the dominant aerosol type with presence of ‘dust aerosol’ during summer and autumn seasons. Aerosol properties like volume size distribution, single scattering albedo, asymmetry parameter and refractive index suggested the influence of coarse particles (during summer and autumn). Most of the air masses reaching this site transported local and regional emissions, including from beyond Central Asia, explaining the presence of various aerosol types in Dushanbe’s atmosphere. The seasonal aerosol radiative forcing efficiency (ARFE) in the atmosphere was found high (>100 Wm⁻²) and consistent throughout the year. Consequently, this resulted in similar seasonally coherent high atmospheric solar heating rate (HR) of 1.5 K day⁻¹ during summer-autumn-winter, and ca. 0.9 K day⁻¹ during spring season. High ARFE and HR values indicate that atmospheric aerosols could exert significant implications to regional air quality, climate and cryosphere over the central Asian region and downwind Tianshan and Himalaya-Tibetan Plateau mountain regions with sensitive ecosystems.

Polluted urban river systems might be a strong source of atmospheric methane (CH₄) and nitrous oxide (N₂O), but so far only a few urban river systems have been quantified with regard to their source strength for greenhouse gases (GHGs). In this study, we measured loads of dissolved inorganic nitrogen and organic carbon, dissolved oxygen (DO) concentrations, and fluxes of CH₄ and N₂O from an urban river in Beijing, China during the course of an entire year. Fluxes calculated using the floating chamber approach or via the diffusion method with measurements of river water GHG concentrations showed comparable temporal variations. However, the flux magnitude based on the diffusion method was found to strongly depend on the underlying parameterization of the gas transfer velocity. In view of the large differences while applying different methodologies to estimate surface water GHG fluxes further studies are still needed to prove and eventually quantify the systematic errors which are likely caused by either the chamber technique or the approaches of individual diffusion models. For both the floating chamber and the diffusion-based flux estimates, strong seasonal variations in CH₄ and N₂O fluxes from the river surface were observed, with fluxes ranging from 3 to 8374 μg C m⁻² h⁻¹ for CH₄ and 1–3986 μg N m⁻² h⁻¹ for N₂O. The CH₄ fluxes were strongly negatively correlated with the DO concentration (P < 0.01). The highest N₂O fluxes were observed at times with low CH₄ fluxes (i.e., in spring and autumn). Annual CH₄ and N₂O fluxes totaled 19.3–79.4 and 17.4–44.8 kg C (N) ha⁻¹ yr⁻¹, respectively. These high fluxes are in agreement with estimates from the few other studies carried out for urban river systems to date and indicate that urban polluted river systems are a significant regional source of atmospheric GHGs.