Polycyclic aromatic hydrocarbons (PAHs) are bonded organic compounds with numerous structures with different toxicity levels. They can be of low molecular weight with 2-3 rings or high molecular weight with more than four rings and are persistent in nature. They possess high molecular weight and boiling point, hydrophobic with minimal solubility in water, and lipophilic with high solubility in organic solvents. With the gain in molecular weight, their susceptibility to oxidation-reduction decreases. They are generated during incomplete combustion of organic materials. They can be natural, such as forest fires, or artificial agents, such as coal, oil, wood burning, smoke, and auto-emissions. Due to strong molecular bonds and structural complexity, PAHs are highly malignant under normal conditions. They cause environmental damage due to improper handling and disposal in the surrounding air, water, soil, etc. PAH contamination is highly toxic because of mutagenic and potentially immune toxicants, often resulting in higher workplace casualties. Various physical, biological, and chemical processes remediate the PAHs in contaminated land. Indigenous microbial communities can effectively degrade it in-situ or ex-situ conditions. The degradation process depends on the type of microorganism, its life cycle, PAH substrate, pH, temperature, pressure, and the reaction mechanism. The present article discusses current literature, chemistry, natural and anthropogenic sources of generation, impacts on the environment, biota, etc., merits of physical, biological, and chemical remediation mechanisms with emphasis on microbial degradation, and novel options of technology intermix suitable for sustainable remediation outcomes.

Smoldering combustion during wildfires contributes significantly to emissions of pollutants, can burn for days or months, may damage roots and soil, and can transition to flaming combustion. Mitigating these hazards requires an understanding of how physical parameters control smoldering combustion, such as the chemical composition of the fuel. The main organic constituents of biomass are cellulose, hemicellulose, and lignin. Understanding how these constituents influence smoldering is an important step in further developing physics -based models and developing understanding that applies across multiple fuel sources. Previous experimental studies have investigated how varying the amount of cellulose and hemicellulose in fuel influences smoldering behavior, but have not considered the impacts of varying the lignin content. The objective of this study was to identify the influence of lignin on smoldering behavior. This objective was achieved by experimentally and numerically studying the smoldering behavior of various concentrations of lignin in mixtures of cellulose and hemicellulose. These were tested at densities of 200 and 300 kg/m 3 . An infrared camera and thermocouples were used to determine the propagation of the smoldering front in the horizontal and vertical directions, respectively. A one-dimensional reactive porous media model with global chemistry was used to simulate downward smoldering propagation. The horizontal and downward smoldering propagation velocities decrease when more lignin is present due to the slower pyrolysis rates and higher activation energy of lignin. Additionally, results from simulations match this trend for downward propagation. At higher lignin contents, the effect of the mass percentage of cellulose and hemicellulose on downward and horizontal smoldering decreases, indicating that lignin content has the largest impact on smoldering velocities of the three constituents. Increasing the density decreases both the horizontal and vertical propagation velocities due to lower oxygen diffusion and the additional mass being consumed.

The formation of pores due to the spontaneous combustion of coal in the goaf, as well as the damage to the surrounding rock caused by high-temperature roasting, can lead to surface subsidence and even collapse. In addition, incomplete combustion of coal can result in the production of various harmful gases, which may escape into the atmosphere through these cracks and seriously pollute the air. This pollution can exacerbate topsoil subsidence, degrade soil properties, harm surface vegetation, and contaminate surface water and groundwater. As a solution to these issues, liquid carbon dioxide fire prevention and extinguishing technology are being utilized for theoretical analysis of overburden movement in goaf. A three-dimensional distribution model of porosity in caving areas has been constructed. Based on this model, dynamic changes in temperature field and oxygen concentration field during liquid carbon dioxide perfusion are being explored. The rapid vaporization of liquid carbon dioxide into inert gas within the goaf inhibits coal oxidation and heating by forming an inert belt within its diffusion range. Simulation results indicate that injecting liquid carbon dioxide at a 90 degrees angle into the oxidation zone (where oxygen concentration is 7-12%) at a volume of 750 m3h-1 best balances cost considerations with effective injection in mining goafs. Industrial testing has shown that after 65 h of perfusion, CO gas concentration decreased from 790ppm to 41ppm - proving significant fire prevention effects from liquid carbon dioxide application.

The following study analyzed the impact of fertilizing barley with fly ash from biomass combustion grown on two types of soil, Haplic Luvisol (HL) and Gleyic Chernozem (GC), on the properties of starch. The experiment was conducted in 2019 (A) and 2020 (B), and barley was fertilized with ash doses (D1-D6) differing in mineral content. In the tested barley starch samples, the amylose content, the clarity of the paste, and the content of selected minerals were determined. The thermodynamic characteristics of gelatinization and retrogradation were determined using the DSC method. Pasting characteristics, flow curves, and viscoelastic properties of starch pastes were performed. Starches differed in amylose content and paste clarity. The highest gelatinization and retrogradation enthalpy (Delta HG and Delta HR) values were recorded for samples GCD1A and HLD5B. None of the tested factors significantly affected the pasting temperature (PT), but they had a significant impact on the remaining parameters of the pasting characteristics. The average PT value of barley starches was 90.9 degrees C. However, GCD2A starch had the highest maximum viscosity and the highest rheological stability during heating. GCD2A paste was characterized by the highest apparent viscosity. It was shown that all pastes showed non-Newtonian flow and shear-thinning and had a predominance of elastic features over viscous ones. The resulting gels had the characteristics of weak gels. Ash from burning wood biomass is an innovative alternative to mineral fertilizers. It was shown that the use of such soil fertilization influenced the properties of barley starch.

By quantifying the absorption of black carbon (BC), brown carbon (BrC) and the lensing effect, we found that BrC dominates the total absorption at 450 nm, and the largest absorption contribution proportion of BrC could reach 78.3% during heavy pollution. The average absorption enhancement (E-abs) at 530 nm was only 1.38, indicating that BC is not coated well here. The average value of the absorption Angstrom exponent (AAE) between 450 nm and 530 nm was 5.3, suggesting a high concentration of BrC in Wangdu. CHN+ was the greatest contributor to the light absorption of molecules detected in MSOC with a proportion of 12.2-22.4%, in which the polycyclic aromatic nitrogen heterocycles (PANHs) were the dominant compounds. The C6H5NO3 and its homologous series accounted for 3.0-11.3%, and the C15H9N and its homologous series, including one C16H11N and three C17H13N compounds, accounted for 5.1-12.3%. The absorption of these PANHs is comparable to that of nitro-aromatics, which should attract more attention to the impact of climate radiative forcing.

Effective density (peff) is an important property describing particle transportation in the atmosphere and in the human respiratory tract. In this study, the particle size dependency of peff was determined for fresh and photochemically aged particles from residential combustion of wood logs and brown coal, as well as from an aerosol standard (CAST) burner. peff increased considerably due to photochemical aging, especially for soot agglomerates larger than 100 nm in mobility diameter. The increase depends on the presence of condensable vapors and agglomerate size and can be explained by collapsing of chain-like agglomerates and filling of their voids and formation of secondary coating. The measured and modeled particle optical properties suggest that while light absorption, scattering, and the single-scattering albedo of soot particle increase during photochemical processing, their radiative forcing remains positive until the amount of nonabsorbing coating exceeds approximately 90% of the particle mass.

Particulate black carbon (BC) affects global warming by absorbing the solar radiation, by affecting cloud formation, and by decreasing ground albedo when deposited to snow or ice. BC has also a wide variety of adverse effects on human population health. In this article we reviewed the BC emission factors (EFs) of major anthropogenic sources, i.e. traffic (incl. marine and aviation), residential combustion, and energy production. We included BC EFs measured directly from individual sources and EFs derived from ambient measurements. Each source category was divided into sub-categories to find and demonstrate systematical trends, such as the potential influence of fuel, combustion technologies, and exhaust/flue gas cleaning systems on BC EFs. Our review highlights the importance of society level emission regulation in BC emission mitigation; a clear BC emission reduction was observed in ambient studies for road traffic as well as in direct emission measurements of diesel-powered individual vehicles. However, the BC emissions of gasoline vehicles were observed to be higher for vehicles with direct fuel injection techniques (gasoline direct injection) than for vehicles with port-fueled injection, indicating potentially negative trend in gasoline vehicle fleet BC EFs. In the case of shipping, a relatively clear correlation was seen between the engine size and BC EFs so that the fuel specific BC EFs of the largest engines were the lowest. Regarding the BC EFs from residential combustion, we observed large variation in EFs, indicating that fuel type and quality as well as combustion appliances significantly influence BC EFs. The largest data gaps were in EFs of large-scale energy production which can be seen crucial for estimating global radiative forcing potential of anthropogenic BC emissions. In addition, much more research is needed to improve global coverage of BC EFs. Furthermore, the use of existing data is complicated by different EF calculation methods, different units used in reporting and by variation of results due to different experimental setups and BC measurement methods. In general, the conducted review of BC EFs is seen to significantly improve the accuracy of future emission inventories and the evaluations of the climate, air quality, and health impacts of anthropogenic BC emissions.

Fuel combustion provides basic energy for the society but also produces CO2 and incomplete combustion products that threaten human survival, climate change, and global sustainability. A variety of fuels burned in different facilities expectedly have distinct impacts on climate, which remains to be quantitatively assessed. This study uses updated emission inventories and an earth system model to evaluate absolute and relative contributions in combustion emission-associated climate forcing by fuels, sectors, and regions. We showed that, from 1970 to 2014, coal burned in the energy sector and oil used in the transportation sector contributed comparable energies consumed (24 and 20% of the total) but had distinct climate forcing (1 and 40%, respectively). Globally, coal burned for energy production had negative impacts on climate forcing but positive effects in the residential sector. In many developing countries, coal combustion in the energy sector had negative radiative forcing (RF) per unit energy consumed due to insufficient controls on sulfur and scattering aerosol levels, but oils in the transportation sector had high positive RF values. These results had important implications on the energy transition and emission reduction actions in response to climate change. Distinct climate efficiencies of energies and the spatial heterogeneity implied differentiated energy utilization strategies and pollution control policies by region and sector.

Carbonaceous particles are an important radiative forcing agent in the atmosphere, with large temporal and spatial variations in their concentrations and compositions, especially in remote regions. This study reported the delta C-14 and delta C-13 of total carbon (TC) and water-insoluble particulate carbon (IPC) of the total suspended particles (TSP) and PM2.5 at a remote site of the eastern Tibetan Plateau (TP), a region that is influenced by heavy air pollution from Southwest China. The average organic carbon and elemental carbon concentrations of TSP samples in this study were 3.20 +/- 2.38 mu g m(-3) and 0.68 +/- 0.67 mu g m(-3), respectively, with low and high values in summer and winter, respectively. The fossil fuel contributions of TC in TSP and PM2.5 samples were 18.91 +/- 7.22% and 23.13 +/- 12.52%, respectively, both of which were far lower than that in Southwest China, indicating the importance of non-fossil contributions from local sources. The delta C-13 of TC in TSP samples of the study site was -27.06 +/- 0.96 parts per thousand, which is between the values of long-range transported sources (e.g., Southwest China) and local biomass combustion emissions. Therefore, despite the contribution from the long-range transport of particles, aerosols emitted from local biomass combustion also have an important influence on carbonaceous particles at the study site. The findings of this work can be applied to other remote sites on the eastern TP and should be considered in related research in the future.

The Tibet Autonomous Region in China is a unique place with high altitude and special Tibetan culture. The residents have different living habits and domestic fuels from those in other parts of China, however, knowledge on the emission characteristics of local residential fuels remain poorly understood until now. In this study, nine popular residential fuels in the Tibet are burned in situ to study the aerosol chemical compositions, mass spectral signatures, and emission characteristics from their burning emissions. Overall, emissions of particulate and gaseous pollutants depend strongly on the burning conditions, in addition to the fuel constituents themselves. Burning the biofuels of yak dung, WeiSang mixture fuels, and two powdery Tibetan incenses with relatively low combustion efficiencies can emit large amounts of CO and aerosols, especially organic aerosols (>90%) with large diameters. In contrast, burning of wood, coal, ghee lamp, stick-like Tibetan incense, and diesel can release abundant CO2 but fewer aerosols from their flaming combustion. A comprehensive database consisting of the high-resolution mass spectra of organics and emission factors of multiple chemical components are established. Distinctly different mass spectral signatures are found among the different fuels, in particularly those unique Tibetan biofuels. All these findings have significant implications for the identification of aerosol sources, compilation of pollutant emission inventories, and assessment of potential environment effects in this remote region.