A 150-year record of black carbon (soot and char) and polycyclic aromatic compounds deposition in Lake Phayao, north Thailand

Tracking the history of polycyclic aromatic compounds in London through a River Thames sediment core and ultrahigh resolution mass spectrometry

Polycyclic aromatic compounds (PACs), including polycyclic aromatic hydrocarbons (PAHs) and heteroatom-containing analogues, constitute an important environmental contaminant class. For decades, limited numbers of priority PAHs have been routinely targeted in pollution investigations, however, there is growing awareness for the potential occurrence of thousands of PACs in the environment. In this study, untargeted Fourier transform ion cyclotron resonance mass spectrometry was used for the molecular characterisation of PACs in a sediment core from Chiswick Ait, in the River Thames, London, UK. Using complex mixture analysis approaches, including aromaticity index calculations, the number of molecular PAC components was determined for eight core depths, extending back to the 1930s. A maximum of 1676 molecular compositions representing PACs was detected at the depth corresponding to the 1950s, and a decline in PAC numbers was observed up the core. A case linking the PACs to London's coal consumption history is presented, alongside other possible sources, with some data features indicating pyrogenic origins. The overall core profile trend in PAC components, including compounds with oxygen, sulfur, nitrogen, and chlorine atoms, is shown to broadly correspond to the 16 priority PAH concentration profile trend previously determined for this core. These findings have implications for other industry-impacted environments.

Infrared Spectrum of the Pyrene Anion in the CH Stretching Region

In this work, we report the infrared spectrum of the pyrene anion, measured using messenger tagging with up to three Ar atoms. We assign the spectrum using density functional theory and vibrational perturbation theory. We discuss our results in the context of computed and experimental spectra from the literature as well as recent observations from astronomical sources, addressing the question of whether polycyclic aromatic hydrocarbon anions could contribute to the strong infrared emission bands at 3.29 μm from carbon-rich regions of space.

Competition between Water-Water Hydrogen Bonds and Water-π Bonds in Pyrene-Water Cluster Anions

We present infrared spectra and density functional theory calculations of hydrated pyrene anion clusters with up to four water molecules. The experimental spectra were acquired by using infrared Ar messenger photodissociation spectroscopy. Water molecules form clusters on the surface of the pyrene, forming hydrogen bonds with the π-system. The structures of the water clusters and their interaction with the π-system are encoded in OH stretching vibrational modes. We find that the interactions between water molecules are stronger than the interactions between water molecules and the π-system. While all clusters show multiple conformers, three- and four-membered rings are the lowest energy structures in the larger hydrates.

Heterogenous distribution and burial flux of black carbon in Chinese lakes and its global implication

Black carbon (BC) plays a crucial role in global carbon cycle and climate change. However, its source and burial flux in environments are not well constrained. Here, we investigated surface sediments from 22 Chinese lakes across wide geographical areas and different socioeconomic status. The BC content accounts for 0.09-10.5 % of total organic carbon (TOC), and its average 14C age is older than that of TOC by 1640 years. The application of δ13C-based MixSIAR model shows that the contribution of fossil fuel combustion is highest in the most developed Eastern China (85.7 %) and lowest in the rural Qinghai-Tibetan Plateau (51.4 %), which is corroborated by the results from 14C-based two endmember mixing model. The BC data from this study and literatures suggest that the current BC burial flux is 126.4 ± 15.8 Gg year-1 in Chinese lakes, and approximately 2987 ± 1022 Gg year-1 in global lakes. Globally, lakes accumulate 1.2 %-6.4 % of the total BC production and thus are an important and heterogenous BC sink.

Sediment record of polycyclic aromatic compounds and black carbon over the last ~400 years in Sanjiaolongwan Maar Lake, northeast China

Fuel usage is an important catalyst for socio-economic development and human well-being. Human activities have resulted in significant increases in emissions from biomass burning (BB) and fossil fuel (FF) combustion which have significantly adversely affected human, ecosystem, and planetary health in this era of the Anthropocene. Sanjiaolongwan Maar Lake (SJLW), as a typical crater lake, uniquely receives atmospheric deposition from long-distance transport, and thus, its sediments reflect environmental change and human impacts on a broad scale. In this study, the concentrations and compositions of combustion products, including polycyclic aromatic compounds (PACs, i.e., polycyclic aromatic hydrocarbons (PAHs) and their oxygenated (OPAHs) and nitrogen heterocyclic derivatives (AZAs)) and black carbon (BC and its constituents char and soot), in SJLW over the past 400 years were investigated. The results showed that the PACs and soot concentrations and fluxes in SJLW have rapidly increased since 1950. The concentrations of the total PACs increased ~4 times after the 1950s. Such a fast increase is consistent with the rapid industrialization after the establishment of the People's Republic of China (PRC), which has further accelerated beginning with the implementation of the reform and opening up policy of the PRC in 1978. Moreover, the variations in the compositions of PACs, as well as the decrease in the char/soot ratio, demonstrate a transition in energy usage from BB to FF combustion. The decrease in the benzo[e]pyrene/benzo[a]pyrene ratio indicated an increase in local emissions (because of increasing industrialization in northeast China). The temporal profile of perylene concentrations, fluxes, and perylene/5-ring PAHs ratios strongly suggest that perylene mainly originated from non-pyrogenic sources. The records of PACs and BC in SJLW offer valuable perspectives on human impacts and provide important references for the start of the Anthropocene.

Temporal trends, sources, and ecological risk of residual organochlorine pesticides (OCPs) in sediment core from the Dongping Lake, North China

A sedimentary record of the 19 organochlorine pesticides (OCPs) pollutants from Dongping Lake, north China, is presented in this study. According to the dating of core sediment and OCP content analysis in samples, from 1904 to 2016, the total concentration of OCPs varied from undetectable levels (n.d.) to 33.1 ng/g. The OCP concentration was first detected in the samples of 1938, and then gradually increased to a peak level in 2000 thereafter decreased until 2016. Among the detected OCPs, hexachlorocyclohexanes (HCHs) and dichlorodiphenyltrichloroethanes (DDTs) were the predominant and the most frequently detected contaminants in the core sediment, with concentrations ranging from n.d. to 16.9 ng/g and from n.d. to 8.8 ng/g, respectively. The distribution of OCPs in the sediments was affected by organic carbon concentration, showing a significant positive correlation (r = 0.93, p < 0.001), especially for HCHs (r = 0.98, p < 0.001). The source analysis showed that HCH contamination mainly derived from historical use of technical HCHs, while in recent years, it derived from lindane usage. DDT pollution was attributed to historical use of technical DDTs, as well as the microbial degradation of historic DDT residues. Finally, risk analysis was performed for OCPs in sediment cores based on sediment quality guidelines from the Canadian Council of Ministers of the Environment, showing that DDTs presented a high ecological toxicity risk during the period of 1959-2010.

A novel biomass pyrogenic index and its application coupled with black carbon for improving polycyclic aromatic hydrocarbon source identification

To accurately subdivide the sources of polycyclic aromatic hydrocarbons (PAHs), the composition characteristics of 36 total polycyclic hydrocarbons (T-PAHs; 16 parent PAHs and 20 alkylated PAHs [A-PAHs]) in biomass-residue samples were analyzed. A novel biomass pyrogenic index (BPI) was defined based on A-PAH-fingerprinting differences between biomass-combustion and petroleum sources of PAHs and the sum of the concentrations of pyrene, fluoranthene, benzo[a]anthracene, and alkylated homologs) divided by the ∑value of EPA PAHs with 2-3 rings. BPIs of < 0.5 and > 0.5 indicated that the PAHs originated mainly from biomass combustion and petroleum, respectively. And the ∑targeted A-PAH pairs influencing the BPI/black carbon (BC) ratio was used to identify PAH sources in surface-sediment samples, using 0.5 as the threshold to distinguish between different sources across the strait. The columnar sediments were used to verify the accuracy of two source-identification methods. The results revealed that the main PAH sources changed since 2005, which is highly consistent with those obtained using positive matrix factors and a changing trend in the main types of local energy use. These results highlight the significance of A-PAHs in accurately identifying PAH sources and suggest that applying compositional differences in BC from different sources for PAH-source identification merits further study.

Nonhomologous Black Carbon Decoupled Char and Soot Sequestration Based on Stable Carbon Isotopes in Tibetan Plateau Lake Sediment

Combustion-derived black carbon (BC) is an important component of sedimentary carbon pool. Due to different physicochemical properties, determining the source of char and soot is crucial for BC cycling, especially for nonhomologous char and soot in the Tibetan Plateau (TP). This study analyzed the sequestration and source of BC, char, and soot in the Dagze Co (inner TP) sediment core via the content and δ¹³C, revealing the biomass and fossil fuel driving on nonsynchronous char and soot and their response to local anthropogenic activities and atmospheric transmission. The results showed that BC concentration increased from 1.19 ± 0.35 mg g^-1 (pre-1956) to 2.03 ± 1.05 mg g^-1 (after 1956). The variation of char was similar to BC, while nonhomologous growth was detected in char and soot (r = 0.29 and p > 0.05). The source apportionment showed that biomass burning for 71.52 ± 10.23% of char and promoted char sequestration. The contribution of fossil fuel combustion to soot (46.67 ± 14.07%) is much higher than char (28.48 ± 10.23%). Redundancy analysis confirmed that local anthropogenic activities significantly influenced BC burial and atmospheric transport from outside TP-regulated BC burial. The contribution of biomass and fossil fuels to nonsynchronous char and soot is conducive to understanding the anthropogenic effect on BC burial in the TP.

Source apportionment of polycyclic aromatic hydrocarbons (PAHs) in a sediment core from Lake Dagze Co, Tibetan Plateau, China: Comparison of three receptor models

Receptor models are a useful tool for identifying sources of polycyclic aromatic hydrocarbons (PAHs) in multiple environmental media. In this study, three different receptor models (including the principal component analysis-multiple linear regression (PCA-MLR), positive matrix factorization (PMF), and Unmix models) were used to apportion the sources of 16 priority PAHs in a sediment core of Lake Dagze Co. The ∑PAHs (sum of all 16 measured PAHs) concentrations ranged from 51.89 to 132.82 ng/g with an average of 80.39 ng/g. The ∑PAHs were dominated by 2-3 ring PAHs, accounting for 80.12% on average, thereby indicating that they mainly originated from biomass and coal combustion and/or from long-range atmospheric transportation. The three models produced consistent source apportionment results. The greatest contributor to ∑PAHs was biomass combustion, followed by coal combustion, vehicle emissions, and petrogenic sources. Moreover, the temporal variation of the common sources was well-correlated among models. The multi-method comparison and evaluation results showed that all three models were useful tools for source apportionment of PAHs, with the PMF model providing better results than the PCA-MLR and Unmix models. The temporal trends of factor contributions were verified by PAHs with different ring numbers. Significant correlations were found between the simulated concentrations of each source factor and the PAHs with different ring numbers (P<0.01), except for the petrogenic source identified by the Unmix model (P>0.05). This study can provide useful information for further investigation of source apportionment of PAHs in the sediment cores.

Oxygenated polycyclic aromatic hydrocarbons in the surface water environment: Occurrence, ecotoxicity, and sources

Oxygenated polycyclic aromatic hydrocarbons (OPAHs) have been ubiquitously detected in atmospheric, soil, sediment, and water environments, some of which show higher concentrations and toxicities than the parent polycyclic aromatic hydrocarbons (PAHs). The occurrence, source, fate, risks and methods of analysis for OPAHs in the atmosphere, soil, and the whole environment (comprising the atmosphere, soil, water, and biota) have been reviewed, but reviews focusing on OPAHs in the water environment have been lacking. Due to the higher polarity and water solubility of OPAHs than PAHs, OPAHs exist preferentially in water environments. In this review, the occurrence, ecological toxicity and source of OPAHs in surface water environments are investigated in detail. Most OPAHs show higher concentrations than the corresponding PAHs in surface water environments. OPAHs pose non-ignorable ecological risks to surface water ecosystems. Wastewater treatment plant effluent, atmospheric deposition, surface runoff, photochemical and microbiological transformation, and sediment release are possible sources for OPAHs in surface water. This review will fill important knowledge gaps on the migration and transformation of typical OPAHs in multiple media and their environmental impact on surface water environments. Further studies on OPAHs in the surface environment, including their ecotoxicity with the co-existing PAHs and mass flows of OPAHs from atmospheric deposition, surface runoff, transformation from PAHs, and sediment release, are also encouraged.

Grey Correlation Analysis of Haze Impact Factor PM2.5

In recent years, frequent severe haze weather has formed in China, including some of the most populated areas. We found that these smog-prone areas are often relatively a “local climate” and aim to explore this series of scientific problems. This paper uses remote sensing and data mining methods to study the correlation between haze weather and local climate. First, we select Beijing, China and its surrounding areas (East longitude 115°20′11″–117°40′35″, North latitude 39°21′11″–41°7′51″) as the study area. We collected data from meteorological stations in Beijing and Xianghe from March 2014 to February 2015, and analyzed the meteorological parameters through correlation analysis and a grey correlation model. We study the correlation between the six influencing factors of temperature, dew point, humidity, wind speed, air pressure and visibility and PM2.5, so as to analyze the correlation between haze weather and local climate more comprehensively. The results show that the influence of each index on PM2.5 in descending order is air pressure, wind speed, humidity, dew point, temperature and visibility. The qualitative analysis results confirm each other. Among them, air pressure (correlation 0.771) has the greatest impact on haze weather, and visibility (correlation 0.511) is the weakest.

A 110 Year Sediment Record of Polycyclic Aromatic Hydrocarbons Related to Economic Development and Energy Consumption in Dongping Lake, North China

A sedimentary record of the 16 polycyclic aromatic hydrocarbon (PAH) pollutants from Dongping Lake, north China, is presented in this study. The influence of regional energy structure changes for 2–6-ring PAHs was investigated, in order to assess their sources and the impact of socioeconomic developments on the observed changes in concentration over time. The concentration of the ΣPAH₁₆ ranged from 77.6 to 628.0 ng/g. Prior to the 1970s, the relatively low concentration of ΣPAH₁₆ and the average presence of 44.4% 2,3-ring PAHs indicated that pyrogenic combustion from grass, wood, and coal was the main source of PAHs. The rapid increase in the concentration of 2,3-ring PAHs between the 1970s and 2006 was attributed to the growth of the urban population and the coal consumption, following the implementation of the Reform and Open Policy in 1978. The source apportionment, which was assessed using a positive matrix factorization model, revealed that coal combustion was the most important regional source of PAHs pollution (>51.0%). The PAHs were mainly transported to the site from the surrounding regions by atmospheric deposition rather than direct discharge.