Water-soluble Organic Carbon Research Articles

Highly significant impact of mineral dust on aerosol hygroscopicity at New Delhi

All conventional hygroscopicity parameter (κ) estimates are based on ammonium salts being the dominant salts, besides sea salt at marine locations. This grossly underestimates κ for highly polluted cities like New Delhi which is subjected to high mineral dust. To validate this hypothesis, the impact of mineral dust on κ was quantified following two mathematical approaches based on Mann-Kendall's test which differed in the sequence followed for compound formation. This leads to a remarkably high increment in κ, on an average of 57% and 63.5% during the day and night respectively, for the period Dec 2012–2014 and is based on the detailed chemical speciation of PM2.5 data. The inter-comparison of κ obtained from various analytical methods challenge the traditional way of estimating κ by including the chemical composition of a few dominant species and ignoring the others without paying any heed to the dependence of κ on Temperature (T) and Relative Humidity (RH). An increase in the ratio of water-soluble organic carbon to organic carbon lessened the impact of mineral dust on κ. The insolubility of calcium salts also decreased the effect of mineral dust, but at the same time lead to MgCl2 formation which augmented the estimated κ. The highest obtained κ was 0.82 (on 23/7/2014 during the night). The impact of mineral dust was also found to be significant for two other Indian (Durg and Kanpur) and Chinese (Xian and Beijing) cities for both PM1 and PM2.5 regimes. The high value of κ and impact of mineral dust on κ can be crucial in Cloud Condensation Nuclei (CCN) estimation at polluted sites subjected to mineral dust and thus impact precipitation quantification by Global Climatic models (GCMs), lead to visibility deterioration and affect the indirect radiative forcing.

Carbonaceous Fractions Contents and Carbon Stable Isotope Compositions of Aerosols Collected in the Atmosphere of Montreal (Canada): Seasonality, Sources, and Implications

With the objective of better understanding the sources and dynamics of carbonaceous fractions of the aerosols present in the atmosphere of Montreal, we implemented here an online wet oxidation/isotope ratio mass spectrometry (IRMS) method to simultaneously measure both water-soluble organic carbon (WSOC) content and the corresponding δ13C of aerosol samples collected at four monitoring stations over a 1-year period representing distinct types of environmental conditions (i.e., background, road traffic, industrial, and downtown). We coupled these data with the corresponding concentrations of other carbon fractions: total carbon (TC), elemental carbon plus organic carbon (EC + OC), and carbonates. Results show that TC (6.64 ± 2.88 μg m–3), EC + OC (4.98 ± 2.23 μg m–3), and carbonates (1.71 ± 1.09 μg m–3) were characterized by lower concentrations in winter and higher ones between spring and early autumn, with all fractions expectedly showing significantly lower concentrations for aerosols collected at the background station. We observed a seasonal dependence of the δ13CEC+OC (−25.31 ± 0.94‰) with the EC + OC/total suspended particles (TSP) ratio: (i) an increase of the ratio during late spring, summer and early autumn associated to road traffic emissions characterized by a δ13C of ∼−25‰ and (ii) lower ratios during the winter months indicating the influence of two distinct emission sources, a first one with a δ13C ∼−27‰, suggesting the local influence of combined biomass burning from residential heating and of fossil fuel combustion, and a second one with a δ13C ∼−21‰, likely related to more regional emissions. WSOC (1.14 ± 0.67 μg m–3) presented a similar seasonal pattern for all monitoring stations, with low concentrations in winter, early spring and late autumn that rapidly increased until summer. Our results indicate that this seasonality is controlled by higher anthropogenic contributions from southern Canada and northeastern United States regions and probably from biogenic emissions during the warm months. Moreover, δ13CWSOC (−25.08 ± 1.47‰) showed a 13C-depletion in summer, indicating higher fossil fuel and biogenic contributions, whereas the higher isotope compositions observed in winter may result from the photochemical aging of regional aerosols. Ultimately, we identified the influence of local industrial emissions late in 2013 as well as the impact of aerosol emissions associated to the Lac-Mégantic rail disaster that occurred on July 6, ∼200 km east of Montreal.

Assessment of long-range oriented source and oxidative potential on the South-west shoreline, Korea: Molecular marker receptor models during shipborne measurements

In order to determine the quantitative contributions of PM2.5 on the South-west shoreline of Korea, filter based samplings were conducted in the summertime of 2017 and 2018 (total 32 days) via shipborne measurements using both a high volume and middle volume air sampler. Water-soluble organic carbon, water-soluble ions, organic carbon and elemental carbon, elemental species, and organic molecular markers by Liquid Chromatography–tandem Mass Spectrometry were utilized to characterize the collected substrates. The current study investigates the (1) chemical characteristics of PM2.5, (2) source apportionment using positive matrix factorization (PMF), and (3) relationship between sources and the dithiothreitol (DTT) assay during the two sampling periods. A mean PM2.5 concentration of 19.3 μg/m3 was observed along the entire sampling route. The ratio of water-soluble to organic carbon implies that secondary aerosol formation is dominant. The result of methanesulfonic acid (MSA) suggests the contribution of a marine-oriented biogenic source of PM2.5. The PMF source apportionment model showed six source categories with reasonably stable profiles: 1) sulfate-rich, 2) MSA-rich, 3) nitrate-rich, 4) secondary organic, 5) continental, and 6) biomass burning sources. The PMF showed three strong events (i.e., long-range transport, mixed (ocean and long-range stay), and domestic origin events) in the contributions of sources, as well as a dependence on wind transport. Higher associations with DTT oxidative potential normalized to PM2.5 mass concentration (DTT–OPm) related to long-range transport, hence, confirming the impacts of the highest intrinsic oxidative potential.

Kinetics comparison and insight into structure-performance correlation for leached biochar gasification

• Isothermal prediction based on model-free method was established. • Kinetic parameters form model-free and model-fitting method were compared. • Gasification mechanism was revealed from carbon and pore structure evolution. • The fractal dimension D 1 was related with amorphous structure. • Mesopore SSA increased by hundred times whereas active sites changed insignificantly. Biomass gasification integrated with leaching pretreatment can be conducive to the sustainable energy system. In this work, the biochar gasification was studied from structure to reactivity with the consideration of leaching pretreatment. The biochar was prepared from raw and leached corn straw (CS) and corncob (CC) in a fixed bed reactor. The gasification was performed in thermogravimetric analyzer with the emphasis on kinetic parameters comparison and reactivity prediction. The carbon and pore structure were investigated to reveal gasification mechanism. The prediction procedure based on model-free method was proposed. From the results, compared with CS, leaching pretreatment reduced gasification reactivity of CC considerably according to reactivity index and reactivity prediction. The random pore model showed the best fitting performance. Furthermore, the leaching pretreatment reduced inorganics (mainly K) in CS and CC, and removed water-soluble organics (pectin) in CC. The active sites and surface roughness in leached biochar decreased accordingly. The CO 2 gasification can activate initial biochar after pyrolysis. Specifically, the specific surface area of mesopore increased by hundred times and more active sites were also generated. However, as the gasification proceeding, the active sites and the fractional dimensions changed insignificantly for both raw and leached biochar. The leaching pretreatment mainly promoted the micropore development during gasification. The pore structure evolution was consistent with the carbon structure, which appeared to be correlated with the kinetic analysis. The research gives new insight into structure-performance correlation of biomass gasification and provides the implication for sustainable energy system based on gasification technology.

Light-absorbing Properties and Sources of PM2.5 Organic Components at a Suburban Site in Northern Nanjing

The light absorption of organic components in PM2.5 was investigated at a suburban site in northern Nanjing from September 2018 to September 2019, and PM2.5 compositional data and principal component analysis (PCA) were used to identify the sources of light-absorbing organic carbon (brown carbon, BrC). The results showed that the average light absorption coefficients of water-soluble organic carbon (WSOC) and methanol extractable organic carbon (MEOC) were (3.22±2.18) Mm-1 (Abs365,w) and (7.69±4.93) Mm-1(Abs365,m), respectively. Significant correlations were observed between Abs365,w and mass concentrations of WSOC (r=0.72, P<0.01) and between Abs365,m and mass concentrations of MEOC (r=0.62, P=0.04). Both Abs365,w and Abs365,m exhibited seasonal variations, with higher values during winter than during summer,and higher diel variations at night than during the day. This can be attributed to meteorological characteristics during the winter and nighttime, i.e., decreased boundary layer height and increased atmospheric stability, enhanced primary emissions in winter,and stronger photobleaching effects during the summer and during the day. The annual average Abs365,m/Abs365,w ratio (2.60±0.92) was much larger than the average mass ratio of MEOC/WSOC (1.37±0.30), indicating that the water-insoluble fraction of MEOC had a stronger light absorption effect and dominated BrC absorption. No strong correlation (r<0.60) was observed between WSOC, MEOC, Abs365,m, and mass concentrations of K+, indication that biomass burning was not the main source of BrC in the study location. The mass absorption efficiency of WSOC (MAE365,w) and MEOC (MAE365,m) and their ratios (MAE365,m/MAE365,w) showed similar seasonal variations to Abs365. The average MAE365 value of the water-insoluble fraction of MEOC (4.10±5.15) m2·g-1 was 6.0 and 2.9 times higher than that of MAE365,w and MAE365,m, respectively, suggested that BrC absorption was primarily attributable to water-insoluble components. In comparison to the absorption Ångström exponent of WSOC (ÅWSOC), ÅMEOC displayed marked temporal variability, which might be related to the seasonal variation in the emission of water-insoluble chromophores. According to the PCA results, the light absorption of PM2.5 organic was mainly attributed to secondary formation and anthropogenic primary emissions rather than biomass burning.

Characteristics and Influencing Factors of the Microbial Concentration and Activity in Atmospheric Aerosols over the South China Sea

Oceans are important sources of microbes in atmospheric aerosols; however, information about the characteristics of airborne microbes and their influencing factors over oceans is lacking. Here we report the characteristics of the microbial abundance and activity in aerosols sampled near the sea surface over the South China Sea (SCS) from May to June 2016. The airborne microbial concentration range in the aerosols was 1.68×105 to 4.84×105 cells m−3 over the SCS, reflecting an average decrease of 40%–54% over the SCS compared with that in the samples from the coastal region of Qingdao. About 63%–76% of the airborne microbes occurred in coarse particles (> 2.1 µm), with a variable size distribution over the SCS. The microbial activity range in aerosols, measured by the fluorescein diacetate (FDA) hydrolysis method, was 2.09–11.97 ng m−3 h−1 sodium fluorescein (SF) over the SCS, which was 15%–79% lower than that over the coastal region. These values reflected a different spatial distribution over the SCS from that of the microbial concentration. Except for certain samples, all samples had 68% of the microbial activity occurring in coarse particles. Correlation analysis showed that the microbial abundance and activity were positively correlated with the aerosol, organic carbon (OC), and water-soluble organic carbon (WSOC) concentrations, indicating that the airborne microbes may be related to the reactions of certain water-soluble organic chemicals in the atmosphere. Moreover, the concentrations of airborne microbes were significantly negatively correlated with the horizontal offshore distance. The microbial concentration and activity were significantly correlated with wind speed.

Molecular composition and optical property of humic-like substances (HULIS) in winter-time PM2.5 in the rural area of North China Plain

In order to distinguish the role of organic composition in haze episodes frequently happening in the North China Plain (NCP), the molecular composition, sources and optical property of humic-like substances (HULIS) in winter-time PM2.5 in a rural area in NCP were investigated. Fifty-five p.m.2.5 samples were collected in the day and night time from Wangdu County (a typical rural area in NCP) in Hebei province from November 4 to December 29 in 2017, and HULIS-C, OC/EC, water-soluble organic carbon (WSOC), water soluble ions and levoglucosan were simultaneously analyzed. The average concentrations of HULIS-C were 5.75 ± 2.73 μg m−3 and 7.39 ± 3.35 μg m−3 in daytime and nighttime, contributing 59 wt% and 55 wt% to WSOC, respectively. Biomass burning, coal combustion and secondary formation were identified as the main sources of HULIS. The values of Ångström absorption exponent (AAE) and mass absorption efficiencies at 365 nm (MAE365) of HULIS were in a moderate level compared with other areas and primary source (biomass burning and coal combustion). Three fluorescent components of HULIS were classified according to the excitation-emission matrix (EEM) combined with parallel factor model (PARAFAC): C1 (less oxygenated humic-like substance), C2 (highly oxygenated humic-like substance) and C3 (protein-like substance). Pearson's correlation coefficient indicated that C2 may be the dominant substance affecting the light absorption properties of HULIS and C3 contributed most to the total fluorescence intensity. FT-ICR MS identified 1839 and 2777 compound species of HULIS for lightly polluted sample and heavily polluted samples, respectively, and CHO/CHNO compounds were the main parts of HULIS in the ESI (−) mode. Lignin-like (64% and 62%) and protein/amino sugars (17% and 18%) species accounted higher proportions of HULIS.

Molecular Comparison of Solid-Phase Extraction and Liquid/Liquid Extraction of Water-Soluble Petroleum Compounds Produced through Photodegradation and Biodegradation by FT-ICR Mass Spectrometry.

We apply two widely used extraction techniques, liquid/liquid extraction and solid-phase extraction with styrene-divinylbenzene polymer with a proprietary nonpolar surface priority pollutant (PPL) to water-soluble compounds generated through photodegradation and biodegradation of petroleum. We compare the molecular composition of bio- and photodegraded water-soluble organic (WSO) acids by 21 T negative-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). We highlight the compositional differences between the two extraction techniques for abiotic and biotic degradation processes and identify known toxic species (naphthenic acids) produced through hydrocarbon biodegradation identified by liquid/liquid extraction (LLE) that are not detected with solid-phase extraction (SPE) of the same sample. Photodegraded WSO compounds extracted by SPE-PPL correspond to species with higher O/C ratio and carbon number compared to LLE extracted compounds. Naphthenic acids, a recalcitrant class of nonaromatic carboxylic acids and known acute toxicants formed through biodegradation of oil, are detected in LLE extracts (up to C30 and double-bond equivalents, DBE < 3) but are not detected in SPE-PPL extracts. This suggests that LLE and SPE-PPL retain different water-soluble oil species based on the dominant type of oil weathering process.

Dry-deposition of inorganic and organic nitrogen aerosols to the Arabian Sea: Sources, transport and biogeochemical significance in surface waters

Air-to-sea deposition of water-soluble total nitrogen (WSTN) can influence the primary productivity in the coastal oceans. Here, we assessed the concentrations of aerosol inorganic (WSIN: NH4+ + NO3−) and WSTN over the Arabian Sea during winter season (SS379:6–24 December 2018). The mean concentrations of NH4+ (109 ± 83 nmol m−3) overwhelm that of NO3− (32 ± 13 nmol m−3) and water-soluble organic nitrogen (WSON: WSTN-WSIN: 86 ± 81 nmol m−3), and contributing to ~50 ± 31% of WSTN mass. Significant linear relationships of WSON with water-soluble organic carbon and NH4+ with non-sea-salt (nss)-K+ is observed suggesting their common origin from biomass burning and fertilizers. Backward air mass trajectories and satellite-based fire counts further revealed their provenance in the Indo-Gangetic Plain and southern India. The concentration of NO3− moderately correlated with nssCa2+ (dust tracer), indicating heterogeneous reactive uptake on mineral aerosol surface. Despite high concentrations, the deposition fluxes of NH4+ (~9.4 ± 7.1 μmol m−2 d−1) and WSON (7.4 ± 7.0 μmol m−2 d−1) are lower than NO3− (27 ± 11 μmol m−2 d−1) because of their predominant fine nature (i.e., strong correlation with nss-SO42−). We also constrained the total annual atmospheric deposition rates of WSIN (0.94 Tg yr−1) and WSON (0.08 Tg yr−1) to the Arabian Sea during the continental outflow (November-April). The maximum dry-deposition of WSON to the Arabian Sea (0.24 Tg yr−1) is twice that of the riverine supply (0.11 Tg yr−1), highlighting the significance of aeolian sources. By using Redfield Stoichiometry, the WSTN deposition (21–73 μmol m−2 d−1) can account for <5.3% of fixed‑carbon by a primary production in the Arabian Sea.

Development of a low-temperature thermal treatment process for the production of plant-growable media using petroleum-impacted dredged sediment

In this study, we investigate the potential of low-temperature thermal treatment to treat petroleum-impacted sediments to produce plant-growable media. The thermal treatment posed a marginal or moderate effect (i.e., 6–47% change) on most of the sediment physicochemical properties, including organic carbon, nutrient contents, and cation exchange capacity, while exhibiting a total petroleum hydrocarbon removal efficiency of 93%. The treatment reduced the bioavailability of heavy metals in the sediment, which was attributed to enhanced physical and/or chemical barriers against heavy metal leaching by sediment particle aggregation and carbonaceous matter formation. Because the oxidation of sediment constituents generated new plant stressors, water-soluble organics and sulfate salts, the thermal treatment by itself was insufficient to produce a medium favorable for the germination and growth of barley. These newly generated stressors were easily removed by water washing post-treatment to yield a final product that showed excellent performance in supporting barley germination and growth. This study demonstrates the benefit of low-temperature thermal treatment to simultaneously achieve control over source-originated contaminants and preserve the ecological value of the dredged sediments. This study also identifies plant stressors that were generated during the treatment, and describes an effective control strategy against them.

Using Isopropanol as a Capping Agent in the Hydrothermal Liquefaction of Kraft Lignin in Near-Critical Water

In this study, Kraft lignin was depolymerised by hydrothermal liquefaction in near-critical water (290–335 °C, 250 bar) using Na2CO3 as an alkaline catalyst. Isopropanol was used as a co-solvent with the objective of investigating its capping effect and capability of reducing char formation. The resulting product, which was a mixture of an aqueous liquid, containing water-soluble organic compounds, and char, had a lower sulphur content than the Kraft lignin. Two-dimensional nuclear magnetic resonance studies of the organic precipitates of the aqueous phase and the char indicated that the major lignin bonds were broken. The high molar masses of the char and the water-soluble organics, nevertheless, indicate extensive repolymerisation of the organic constituents once they have been depolymerised from the lignin. With increasing temperature, the yield of char increased, although its molar mass decreased. The addition of isopropanol increased the yield of the water-soluble organic products and decreased the yield of the char as well as the molar masses of the products, which is indicative of a capping effect.

Characteristics, primary sources and secondary formation of water-soluble organic aerosols in downtown Beijing

Abstract. Water-soluble organic carbon (WSOC) accounts for a large proportion of aerosols and plays a critical role in various atmospheric chemical processes. In order to investigate the primary sources and secondary production of WSOC in downtown Beijing, day and night fine particulate matter (PM2.5) samples in January (winter), April (spring), July (summer) and October (autumn) 2017 were collected and analyzed for WSOC and organic tracers in this study. WSOC was dominated by its moderately hydrophilic fraction and showed the highest concentration in January and comparable levels in April, July and October 2017. Some typical organic tracers were chosen to evaluate the emission strength and secondary formation of WSOC. Seasonal variation of the organic tracers suggested significantly enhanced formation of anthropogenic secondary organic aerosols (SOAs) during the sampling period in winter and obviously elevated biogenic SOA formation during the sampling period in summer. These organic tracers were applied into a positive matrix factorization (PMF) model to calculate the source contributions of WSOC as well as its moderately and strongly hydrophilic portions. The secondary sources contributed more than 50 % to WSOC, with higher contributions during the sampling periods in summer (75.1 %) and winter (67.4 %), and the largest contributor was aromatic SOC. In addition, source apportionment results under different pollution levels suggested that controlling biomass burning and aromatic precursors would be effective to reduce WSOC during the haze episodes in cold seasons. The impact factors for the formation of different SOA tracers and total secondary organic carbon (SOC) as well as moderately and strongly hydrophilic SOC were also investigated. The acid-catalyzed heterogeneous or aqueous-phase oxidation appeared to dominate in the SOC formation during the sampling period in winter, while the photochemical oxidation played a more critical role during the sampling period in summer. Moreover, photooxidation played a more critical role in the formation of moderately hydrophilic SOC, while the heterogeneous or aqueous-phase reactions had more vital effects on the formation of strongly hydrophilic SOC.

Effects of cadmium on soil nitrification in the rhizosphere of Robinia pseudoacacia L. seedlings under elevated atmospheric CO2 scenarios

The individual impacts of elevated CO2 and heavy metals on soil nitrification have been widely reported. However, studies on the combined effects of elevated CO2 and heavy metals on soil nitrification are still limited. Here, a 135-day growth chamber experiment was conducted to investigate the impacts of elevated CO2 and cadmium (Cd) levels on soil nitrification in the rhizosphere of Robinia pseudoacacia L. seedlings. Elevated CO2 combined with Cd pollution generally stimulated ammonia monooxygenase (AMO), hydroxylamine oxidase (HAO), and nitrite oxidoreductase (NXR) activities. Compared to the control, the abundance of ammonia-oxidizing bacteria (AOB) at day 135 and ammonia-oxidizing archaea (AOA) increased significantly (p < 0.05) and the abundance of AOB at days 45 and 90 and that of the nitrite-oxidizing bacteria (NOB) decreased under elevated CO2 + Cd. Elevated CO2 mostly led to a significant (p < 0.05) decrease in soil nitrification intensity in the rhizosphere of R. pseudoacacia exposed to Cd. The effects of Cd, CO2, and their interaction on HAO and NXR activities were significant (p < 0.01). Soil pH, the C/N ratio, water-soluble organic carbon, water-soluble organic nitrogen (WSON), and total carbon were the dominant factors (p < 0.05) affecting nitrifying enzyme activities and nitrification intensity in rhizosphere soils. Elevated CO2 clearly affected AOA, AOB, and NOB community structures and dominant genera by shaping C/N ratio, pH, and Cd and WSON contents in rhizosphere soils under Cd exposure. Overall, the responses of pH, C/N ratio, WSON, and Cd to elevated CO2 led to changes in rhizosphere soil nitrification under the combination of elevated CO2 and Cd pollution.

Molecular Speciation of Size Fractionated Particulate Water-Soluble Organic Carbon by Two-Dimensional Nuclear Magnetic Resonance (NMR) Spectroscopy.

Particulate matter is associated with increased morbidity and mortality; its effects depend on particle size and chemical content. It is important to understand the composition and resultant toxicological profile of particulate organic compounds, the largest and most complex fraction of particulate matter. The objective of the study was to delineate the nuclear magnetic resonance (NMR) spectral fingerprint of the biologically relevant water-soluble organic carbon (WSOC) fraction of size fractionated urban aerosol. A combination of one and two-dimensional NMR spectroscopy methods was used. The size distribution of particle mass, water-soluble extract, non-exchangeable organic hydrogen functional types and specific biomarkers such as levoglucosan, methane sulfonate, ammonium and saccharides indicated the contribution of fresh and aged wood burning emissions, anthropogenic and biogenic secondary aerosol for fine particles as well as primary traffic exhausts and pollen for large particles. Humic-like macromolecules in the fine particle size range included branched carbon structures containing aromatic, olefinic, keto and nitrile groups and terminal carboxylic and hydroxyl groups such as terpenoid-like polycarboxylic acids and polyols. Our study show that 2D-NMR spectroscopy can be applied to study the chemical composition of size fractionated aerosols.

Spatiotemporal Variation In Groundwater Quality Of India During Last 15 Years: A Review

Groundwater resource in this few decades has been challenging in India due to intense agricultural, industrial and mining activities which make groundwater quality exposed to contaminants. This review article deals with results of groundwater quality monitoring and assessment works conducted in India during the year 2000 to 2015. Previously published research articles of study region with the theme of groundwater quality have been discussed for concentrations of heavy metals, ions, water-soluble organics and inorganics along with its associated health impacts. Several methodologies were used for various chemical contaminants quantification and a wide range of statistical approaches was also applied for their source identification and/or apportionment. The major groundwater pollutants were F? , NO? , As, V, Cd, Cr, Cu, Fe, Pb, Co, Mn, Ni, Zn, Polycyclic Aromatic Hydrocarbons (PAHs), Organochlorine Pesticides (OCPs) etc. monitored in India in higher concentration than standard permissible limits regulated by various international and national agencies like World Health Organization (WHO), United States Environmental Protection Agency (USEPA), American Publi c Health Association (APHA) and Bureau of Indian Standards (BIS). Studies reported that millions of people are suffering from chronic heavy metal poisoning causing cancer, cardiovascular diseases, affecting central nervous system, brain, liver, kidney etc., while 1.6 million children expire every year from ailment for which polluted drinking water is a primary cause.

Applications of the RTgill-W1 Cell Line for Acute Whole-Effluent Toxicity Testing: In Vitro-In Vivo Correlation and Optimization of Exposure Conditions.

The cell line RTgill-W1 was evaluated as an in vitro alternative model for acute fish whole-effluent toxicity (WET) testing. We determined the 50% effective concentration (EC50) that reduces the viability of RTgill-W1 cells for selected toxicants commonly found in effluent samples and correlated those values with the respective 50% lethal concentration (LC50) of freshwater (fathead minnow, Pimephales promelas) and marine (sheepshead minnow, Cyprinodon variegatus) fish species obtained from the literature. Excluding low water-soluble organics and the volatile sodium hypochlorite, significant correlations were measured for metal, metalloids, ammonia, and higher water-soluble organics between in vitro EC50 values and in vivo LC50 values for both species. Typically, toxicity studies with RTgill-W1 cells are conducted by adding salts to the exposure medium, which may affect the bioavailability of toxicants. Osmotic tolerance of RTgill-W1 cells was found between 150 and 450 mOsm/kg, which were set as the hypoosmotic and hyperosmotic limits. A subset of the toxicants were then reexamined in hypoosmotic and hyperosmotic media. Copper toxicity decreased in hyperosmotic medium, and nickel toxicity increased in hypoosmotic and hyperosmotic media. Linear alkylbenzene sulfonate toxicity was not affected by the medium osmolality. Overall, RTgill-W1 cells have shown potential for applications in measuring metal, metalloids, ammonia, and water-soluble organic chemicals in acute WET tests, as well as complementing current toxicity identification and reduction evaluation strategies. In the present study, RTgill-W1 cells have been established as a valid animal alternative for WET testing, and we show that through manipulation of medium osmotic ranges, sensitivity to nickel was enhanced. Environ Toxicol Chem 2021;40:1050-1061. © 2020 SETAC.

Comprehensive characterizations of HULIS in fresh and secondary emissions of crop straw burning

The humic-like substances (HULIS) in PM2.5 in fresh and secondary emissions of crop straw burning will result in strong light absorption of atmospheric aerosols in the near-ultraviolet and visible light region. Herein, the relative carbon contents, light absorption properties, fluorescence characteristics, FTIR and 1H NMR spectra of fresh and secondary HULIS in crop straws (wheat, rice, and corn) burning were comprehensively characterized. The results showed that the ratios of carbon contents in HULIS to water-soluble organic carbon and organic carbon (HULIS-C/WSOC and HULIS/OC) of HULIS in secondary emissions of crop straw burning were higher than that in fresh emissions. The MAE365 (mass absorption efficiencies at 365 nm) of secondary HULIS in crop straws burning were larger than that in fresh emissions. Excitation-emission matrix (EEM) spectra indicated that fresh HULIS contained phenol-like substances, which can form light-absorbing substances through secondary conversion. The spectrum of FTIR and 1H-nuclear magnetic resonance (1H NMR) showed that chemical structures of secondary HULIS in crop straws combustion were more complicated and contained more absorbing aromatic groups (e.g. aromatic rings, carbonyl groups, and aliphatic chains). Therefore, the secondary aerosol conversion may cause more aromatic structures in HULIS from crop straws burning, resulting in stronger light absorption abilities.

Sources and light absorption characteristics of water-soluble organic carbon (WSOC) of atmospheric particles at a remote area in inner Himalayas and Tibetan Plateau

Water-soluble organic carbon (WSOC) is an important component of carbonaceous aerosols. Increasing evidences show that WSOC absorbs and scatters sunlight in the atmosphere, which is one of the key components of climate change. Despite numbers of related studies, understanding of basic characteristics of WSOC is limited at remote region, such as the Himalayas and Tibetan Plateau (HTP), one of the remotest regions in the world with weak local anthropogenic activities. In this study, we conducted a year-round investigation of multiple aerosol species at Nam Co, a pristine station in inner part of the HTP. The results showed that the annual mean concentrations of PM2.5 and its WSOC were 8.9 ± 5.4 μg m−3 and 249 ± 111 ng m−3, respectively, which was among the lowest values in the HTP, representing a clean environment. WSOC of PM2.5 and total suspended particle (TSP) samples were mainly derived from combustion emissions and fine particle of local surface soil, respectively, indicating significant contribution of local sources of the HTP to TSP samples. Similarly, due to the influence of surface soil, respective absorption per mass of WSOC at 365 nm (α/ρWSOC) of TSP (1.74 ± 0.94 m2 g−1) was significantly higher than that of PM2.5 (1.22 ± 0.43 m2 g−1). Seasonally, high and low WSOC concentrations and α/ρWSOC values appeared at non-monsoon and monsoon periods, respectively. This study provides observational constraints for related researches such as modelling of the environmental impact of WSOC in the HTP.

Concerted measurements of free amino acids at the Cabo Verde islands: high enrichments in submicron sea spray aerosol particles and cloud droplets

Abstract. Measurements of free amino acids (FAAs) in the marine environment to elucidate their transfer from the ocean into the atmosphere, to marine aerosol particles and to clouds, were performed at the MarParCloud (marine biological production, organic aerosol particles and marine clouds: a process chain) campaign at the Cabo Verde islands in autumn 2017. According to physical and chemical specifications such as the behavior of air masses, particulate MSA concentrations and MSA∕sulfate ratios, as well as particulate mass concentrations of dust tracers, aerosol particles predominantly of marine origin with low to medium dust influences were observed. FAAs were investigated in different compartments: they were examined in two types of seawater underlying water (ULW) and in the sea surface microlayer (SML), as well as in ambient marine size-segregated aerosol particle samples at two heights (ground height based at the Cape Verde Atmospheric Observatory, CVAO, and at 744 m height on Mt. Verde) and in cloud water using concerted measurements. The ∑FAA concentration in the SML varied between 0.13 and 3.64 µmol L−1, whereas it was between 0.01 and 1.10 µmol L−1 in the ULW; also, a strong enrichment of ∑FAA (EFSML: 1.1–298.4, average of 57.2) was found in the SML. In the submicron (0.05–1.2 µm) aerosol particles at the CVAO, the composition of FAAs was more complex, and higher atmospheric concentrations of ∑FAA (up to 6.3 ng m−3) compared to the supermicron (1.2–10 µm) aerosol particles (maximum of 0.5 ng m−3) were observed. The total ∑FAA concentration (PM10) was between 1.8 and 6.8 ng m−3 and tended to increase during the campaign. Averaged ∑FAA concentrations in the aerosol particles on Mt. Verde were lower (submicron: 1.5 ng m−3; supermicron: 1.2 ng m−3) compared to the CVAO. A similar contribution percentage of ∑FAA to dissolved organic carbon (DOC) in the seawater (up to 7.6 %) and to water-soluble organic carbon (WSOC) in the submicron aerosol particles (up to 5.3 %) indicated a related transfer process of FAAs and DOC in the marine environment. Considering solely ocean–atmosphere transfer and neglecting atmospheric processing, high FAA enrichment factors were found in both aerosol particles in the submicron range (EFaer(∑FAA): 2×103–6×103) and medium enrichment factors in the supermicron range (EFaer(∑FAA): 1×101–3×101). In addition, indications for a biogenic FAA formation were observed. Furthermore, one striking finding was the high and varying FAA cloud water concentration (11.2–489.9 ng m−3), as well as enrichments (EFCW: 4×103 and 1×104 compared to the SML and ULW, respectively), which were reported here for the first time. The abundance of inorganic marine tracers (sodium, methanesulfonic acid) in cloud water suggests an influence of oceanic sources on marine clouds. Finally, the varying composition of the FAAs in the different matrices shows that their abundance and ocean–atmosphere transfer are influenced by additional biotic and abiotic formation and degradation processes. Simple physicochemical parameters (e.g., surface activity) are not sufficient to describe the concentration and enrichments of the FAAs in the marine environment. For a precise representation in organic matter (OM) transfer models, further studies are needed to unravel their drivers and understand their composition.

Characteristics of Locally Occurring High PM2.5 Concentration Episodes in a Small City in South Korea

In this study, the ionic and carbonaceous compounds in PM2.5 were analysed in the small residential city of Chuncheon, Korea. To identify the local sources that substantially influence PM2.5 concentrations, the samples were divided into two groups: samples with PM2.5 concentrations higher than those in the upwind metropolitan area (Seoul) and samples with lower PM2.5 concentrations. During the sampling period (December 2016–August 2018), the average PM2.5 was 23.2 μg m−3, which exceeds the annual national ambient air quality standard (15 μg m−3). When the PM2.5 concentrations were higher in Chuncheon than in Seoul, the organic carbon (OC) and elemental carbon (EC) concentrations increased the most among all the PM2.5 components measured in this study. This is attributable to secondary formation and biomass burning, because secondary OC was enhanced and water soluble OC was strongly correlated with K+, EC, and OC. A principal component analysis identified four factors contributing to PM2.5: fossil-fuel combustion, secondary inorganic and organic reactions in biomass burning plumes, crustal dust, and secondary NH4+ formation.