Biogenic Contributions Research Articles

Predominant biogenic contribution of dissolved inorganic carbon in karst rivers, Southwest China

Dissolved inorganic carbon (DIC) holds significant importance within river systems, particularly in karst regions. The concentration of DIC is intricately linked to both biological processes, such as the respiration of organic matter, and geological processes, notably the strength of carbonate weathering. This dual influence exerts a profound impact on regional and global carbon cycles. However, the precise biological and geological origins of DIC in karst rivers remain a subject of debate. In this study, we delineate the sources of DIC in a typical karst catchment (Houzhai catchment) through isotopic analysis coupled with water chemistry examination. The results showed that δ13CDIC and Δ14CDIC variations range from −14.0 ‰ to −7.3 ‰ and − 426 ‰ to −31 ‰, respectively, with average values of −10.5 ‰ and − 180 ‰. Results derived from the isotopic mixing model suggest that approximately 83 % of DIC emanates from the soil CO2, while 17 % originates from carbonate sources. This indicates that biological processes exert a greater influence on DIC within the study area compared to geological processes. Seasonal variation, exemplified by higher DOC concentrations and Δ14CDIC values, alongside with lower DIC concentrations and δ13CDIC values during the wet season indicate increased input from biogenic sources, closely related to temperature and moisture conditions. Our study underscores an unbalanced contribution from biogenic and geogenic sources in karst rivers, highlighting potential inaccuracies in past carbon sink flux calculations. The roles of biogenic and geogenic sources in the carbon cycling of karst rivers, as well as their responses to future climate change, warrant a reevaluation.

Source apportionment and formation of warm season ozone pollution in Chengdu based on CMAQ-ISAM

In this study, the WRF-CMAQ model integrated with BEM urban canopy model was used to simulate the concentrations of Ozone (O3) and its precursors, NOx and VOCs, in warm season of Chengdu, conduct source apportionment and formation analysis. The results show that the O3 in Chengdu exhibits a west-high/east-low spatial pattern, attributable to nearly 40% contribution from boundary sources representing the transport role of the Sichuan Basin, regional sources from districts emitting high precursor concentrations, and increasing biogenic contributions from western areas due to rising BVOCs emissions during the warm season. NOx from traffic and VOCs from industrial sources, both prevalent in Chengdu's high urban density areas, chemically react to form O3, making these sectors primary contributors to O3. NOx photochemical reactions producing O3 occur at 150 m–2500 m with peak generation rates of 10 μg/(m3·hr). Ground-level NO titration removal is most significant during heavy traffic (14:00–21:00), ranging from −70 to −200 μg/(m3·hr). O3 is replenished through similar rates of daytime vertical diffusion and nighttime horizontal advection, correlating with urban density across regions. Controlling Chengdu's warm season O3 requires focusing on long-distance external transport and regional precursor emission reductions, with strategies tailored to local urban characteristics.

Mutagenic atmospheres generated from the photooxidation of NOx with selected VOCs and a complex mixture: Apportionment of aromatic mutagenicity for reacted gasoline vapor

The interaction of sunlight with volatile organic compounds (VOCs) emitted from various sources results in mutagenic photooxidation products that contribute substantially to air pollution. Evaporation of gasoline is one such source of VOCs; however, no studies have evaluated the mutagenicity of the photooxidation products of gasoline vapors or of many of the non-aromatic constituent VOCs of gasoline. Here we determined the mutagenicity in Salmonella TA100 of atmospheres generated in a steady-state atmospheric simulation chamber by irradiating gasoline and individual non-aromatic VOCs in the presence of nitrogen oxides (NOX) in air. In addition to gasoline, we evaluated α-pinene; 2-pentene; ethanol; isobutanol; isoprene; and 2,2,4-trimethylpentane (isooctane). Cells were exposed at the air-agar interface to the atmospheres for 1, 2, 4, 8, or 16 h. Atmospheres generated in the dark were not mutagenic. However, under irradiation all atmospheres other than that of 2,2,4-trimethylpentane were mutagenic, with mutagenic potencies spanning 8.6-fold. The mutagenicity was due exclusively to direct-acting, late-generation photooxidation products. The non-aromatic VOCs studied here contributed little to the mutagenic potency of the photooxidation products of gasoline. However, the sum of the mutagenic potencies of these atmospheres plus those from the photooxidation of some aromatic VOCs in gasoline measured here and elsewhere (Riedel et al., 2018) accounted for 71% of the mutagenic potency of the photooxidation products of gasoline vapor. In photochemical mixtures with strong biogenic contributions, isoprene products may also contribute significantly to mutagenic potency. Strategies to reduce the emissions of gasoline and those VOCs whose photooxidation products are most mutagenic would reduce VOC-associated air pollution and improve public health.

Short-Term Exposure to Fine Particulate Matter and Ozone: Source Impacts and Attributable Mortalities.

Short-term exposure to particles with aerodynamic diameters less than 2.5 μm (PM2.5) and ozone (O3) are important risk factors for human health. Despite the awareness of reducing attributable health burden, region-specific and source-specific strategies remain less explored due to the gap between precursor emissions and health effects. In this study, we isolate the health burden of individual sector sources of PM2.5 and O3 precursors, nitrogen oxides (NOx) and volatile organic compounds (VOCs), across the globe. Specifically, we estimate mortalities attributable to short-term exposure using machine-learning-based daily exposure estimates and quantify sectoral impacts using chemical transport model simulations. Globally, short-term exposure to PM2.5 and O3 result in 713.5 (95% Confidence Interval: 598.8-843.3) thousand and 496.3 (371.3-646.1) thousand mortalities in 2019, respectively, of which 12.5% are contributed by fuel-related NOx emissions from transportation, energy, and industry. Sectoral impacts from anthropogenic NOx and VOC emissions on health burden vary significantly among seasons and regions, requiring a target shift from transportation in winter to industry in summer for East Asia, for instance. Emission control and health management are additionally complicated by unregulated natural influences during climatic events. Fire-sourced NOx and VOC emissions, respectively, contribute to 8.5 (95% CI: 6.2-11.7) thousand and 4.8 (3.6-5.9) thousand PM2.5 and O3 mortalities, particularly for tropics with high vulnerability to climate change. Additionally, biogenic VOC emissions during heatwaves contribute to 1.8 (95% CI: 1.5-2.2) thousand O3-introduced mortalities, posing challenges in urban planning for high-income regions, where biogenic contributions to health burden during heatwaves are 13% of anthropogenic contributions annually. Our study provides important implications for temporally dynamic and sector-targeted emission control and health management strategies, which are of urgency under the projection of continuously increasing energy consumption and changing climate.

Australian Black summer smoke signal on Antarctic aerosol collected between New Zealand and the Ross sea

Open biomass burning (BB) events are a well-known primary aerosol source, resulting in the emission of significant amount of gaseous and particulate matter and affecting Earth's radiation budget. The 2019–2020 summer, known as “Australian Black Summer”, showed exceptional duration and intensity of seasonal wildfires, triggered by high temperatures and severe droughts. Since increasing megafires are predicted due to expected climate changes, it is critical to study the impact of BB aerosol on a large scale and evaluate related transport processes. In this study, five aerosol samples (total suspended particles with a diameter >1 μm) were collected during the XXXV Italian Expedition in Antarctica on board of the R/V Laura Bassi from 6th of January to February 16, 2020, along the sailing route from Lyttelton harbor (New Zealand) to Terra Nova Bay (Antarctica). Levoglucosan and its isomers have been analyzed as markers of BB, together with polycyclic aromatic hydrocarbons (PAHs), sucrose and alcohol sugars. Ionic species and carboxylic acids have been analyzed to support the identification of aerosol sources and its aging. Results showed high levoglucosan concentrations (325–1266 pg m−3) during the campaign, suggesting the widespread presence of smoke in the region, because of huge wildfire releases. Backward trajectories indicated the presence of long-range atmospheric transport from South America, probably carrying wildfires plume, in agreement with literature. Regional sources have been suggested for PAHs, particularly for 3–4 rings' compounds; monosaccharides, sucrose, arabitol, and mannitol were related to marine and biogenic contributions. In a warming climate scenario, more frequent and extensive wildfire episodes are expected in Australia, potentially altering albedo, aerosol radiative properties, and cloud interactions. Therefore, it is crucial to strengthens the investigations on the regional climatic effects of these events in Antarctica.

Authigenic Iron Is a Significant Component of Oceanic Labile Particulate Iron Inventories

AbstractParticulate phases transport trace metals (TM) and thereby exert a major control on TM distribution in the ocean. Particulate TMs can be classified by their origin as lithogenic (crustal material), biogenic (cellular), or authigenic (formed in situ), but distinguishing these fractions analytically in field samples is a challenge often addressed using operational definitions and assumptions. These different phases require accurate characterization because they have distinct roles in the biogeochemical iron cycle. Particles collected from the upper 2,000 m of the northwest subtropical Atlantic Ocean over four seasonal cruises throughout 2019 were digested with a chemical leach to operationally distinguish labile particulate material from refractory lithogenics. Direct measurements of cellular iron (Fe) were used to calculate the biogenic contribution to the labile Fe fraction, and any remaining labile material was defined as authigenic. Total particulate Fe (PFe) inventories varied <15% between seasons despite strong seasonality in dust inputs. Across seasons, the total PFe inventory (±1SD) was composed of 73 ± 13% lithogenic, 18 ± 7% authigenic, and 10 ± 8% biogenic Fe above the deep chlorophyll maximum (DCM), and 69 ± 8% lithogenic, 30 ± 8% authigenic, and 1.1 ± 0.5% biogenic Fe below the DCM. Data from three other ocean regions further reveal the importance of the authigenic fraction across broad productivity and Fe gradients, comprising ca. 20%–27% of total PFe.

Spatial and diurnal variations of aerosol organosulfates in summertime Shanghai, China: potential influence of photochemical processes and anthropogenic sulfate pollution

Abstract. Organosulfates (OSs) are ubiquitous aerosol components, which has seen intense research over years. However, spatial and diurnal variations in OS formation in polluted atmospheres remain poorly understood. In this study, 130 OS species were quantified (or semi-quantified) in ambient fine particulate matter (PM2.5) collected in urban and suburban Shanghai (East China) in the summer of 2021. Isoprene- and monoterpene-derived OSs were dominant OS groups (averaging 51 % and 19 % of total quantified OSs, respectively), likely indicating a large biogenic contribution to OS formation in summer. Most OSs peaked during daytime, while monoterpene-derived nitrooxy-OSs (NOSm) increased during nighttime. Accordingly, OSs were largely produced via daytime formation processes, rather than nighttime chemistry, except for NOSm. Additionally, although OS formation in the urban and suburban areas exhibited similar diurnal variations, the average concentrations of biogenic and anthropogenic OSs decreased significantly from the urban site to the suburban site. Furthermore, we concretized daytime OS formation based on the interactions among OSs, ultraviolet (UV), ozone (O3), and sulfate (SO42-). Indeed, the concentrations of most OSs were significantly correlated with the values of UV[O3][SO42-] during daytime in both urban and suburban Shanghai. In particular, the correlation between major OSs and UV[O3][SO42-] was stronger than the correlation of major OSs with O3 and SO42-; moreover, there was no significant correlation between major OSs and UV. Thus, higher urban OS events were attributed to the enhanced photochemical processes and sulfate level in the urban area. Overall, this study provides field evidence for the influence of photochemical processes and anthropogenic sulfate on OS formation and has important implications for the mitigation of organic particulate pollution.

Insight into decreased ozone formation across the Chinese National Day Holidays at a regional background site in the Pearl River Delta

Investigating the formation mechanism of ozone (O3) during the Chinese National Day Holidays (CNDH, Oct. 1st to 7th) in the background area of megacity clusters provided a valuable opportunity for surveying the relative influence of anthropogenic and biogenic sources on O3 pollution. Here we conducted an intensive observation campaign during Sep. 24 to Oct. 14, 2021 at a regional background site in the Pearl River Delta region, southern China. Results showed that O3 concentrations exhibited a downtrend across the CNDH, with a decreasing rate of 14.8% from prior-CNDH to CNDH and 28.9% from CNDH to post-CNDH. Simulation of O3 photochemical process by using a photochemical box model with the master chemical mechanism (PBM-MCM) indicated that the decreased atmospheric oxidation capacity and decelerated free radical cycling led to a decrease in the net O3 production rate (PO3) across the CNDH. O3 isopleth diagrams and relative incremental reactivity (RIR) analysis revealed that O3 formation (FO3) in prior-CNDH and CNDH was jointly limited by VOCs and NOx, while was VOC-limited in post-CNDH. VOCs was still shown to be the largest contributor to FO3, suggesting VOCs reduction was the most effective way to reduce O3 pollution. Further simulation by combining the PBM-MCM and positive matrix factorization (PMF) model showed that anthropogenic sources have a smaller contribution to the PO3 in CNDH compared to the other periods, showing a significant holiday effect of “decreasing during holidays and rebounding after holidays”. However, due to the more biogenic emission during CNDH, the net PO3 was higher than that post-CNDH. This study improved our understanding of the enhanced biogenic contributions to FO3 in future scenarios of anthropogenic emissions reduction.

Identification of volatile organic compounds and their sources driving ozone and secondary organic aerosol formation in NE Spain

Volatile organic compounds (VOCs) play a crucial role in the formation of ozone (O3) and secondary organic aerosol (SOA). We conducted measurements of VOC ambient mixing ratios during both summer and winter at two stations: a Barcelona urban background station (BCN) and the Montseny rural background station (MSY). Subsequently, we employed positive matrix factorization (PMF) to analyze the VOC mixing ratios and identify their sources. Our analysis revealed five common sources: anthropogenic I (traffic & industries); anthropogenic II (traffic & biomass burning); isoprene oxidation; monoterpenes; long-lifetime VOCs. To assess the impact of these VOCs on the formation of secondary pollutants, we calculated the ozone formation potential (OFP) and secondary organic aerosol formation potential (SOAP) associated with each VOC. In conclusion, our study provides insights into the sources of VOCs and their contributions to the formation of ozone and SOA in NE Spain. The OFP was primarily influenced by anthropogenic aromatic compounds from the traffic & industries source at BCN (38–49 %) and during winter at MSY (34 %). In contrast, the summer OFP at MSY was primarily driven by biogenic contributions from monoterpenes and isoprene oxidation products (45 %). Acetaldehyde (10–35 %) and methanol (13–14 %) also made significant OFP contributions at both stations. Anthropogenic aromatic compounds originating from traffic, industries, and biomass burning played a dominant role (88–93 %) in SOA formation at both stations during both seasons. The only exception was during the summer at MSY, where monoterpenes became the primary driver of SOA formation (41 %). These findings emphasize the importance of considering both anthropogenic and biogenic VOCs in air quality management strategies.

Differentiated Estimation of the 137Cs Content on the Biogenic and Lithogenic Suspended Matter in the Black Sea

Sedimentation transport of 137Cs can lead to the significant accumulation of this radionuclide at depths that could not be reached through the vertical water exchange alone; therefore, a comparative assessment of its contents for different types of suspended matter (SM) and regions of the Black Sea is of particular interest. For this purpose, we have collected samples of SM and seawater at deep-water and coastal stations for the subsequent determination of the 137Cs activity in the surface water layer. To calculate the fraction of lithogenic matter, the potassium content in the SM was additionally determined. The range of 137Cs content on SM at different stations differed by more than an order of magnitude: from 7 to 111 Bq/kg for specific activity, and from 0.03 to 0.69% for its content on SM, in % of the total content in the surface water layer. Stations located farther away from the coast were characterized by the lowest percentage of 137Cs in SM, while its content at the coastal stations was more variable. The comparison of the lithogenic and biogenic contribution to SM and data on 137Cs for different stations suggests that the content of this radionuclide on SM is primarily determined by the dynamic variations of the lithogenic matter. Based on the 137Cs migration on SM, the Black Sea is divided into at least two types of regions. One regions are water areas far removed from sources of lithogenic matter where SM is formed mainly due to the hydrobiont activity. The 137Cs content in SM due to the predominance of biogenic matter and an insignificant concentration of lithogenic matter in this case accounts for hundredths of a percent of its total content in the surface water layer. Other regions are coastal and shelf water basins, which, on the one hand, are subjected to the significant coastal and river lithogenic runoff, and on the other, they are characterized by the elevated trophicity and biological productivity. In these water areas, 137Cs content on SM owing to the variability of biotic and abiotic factors is more variable and can fluctuate from values typical for the open sea to an order of magnitude higher.

Comparison of СO<sub>2</sub> Content in the Atmosphere of St. Petersburg According to Numerical Modelling and Observations

Due to the increase in CO2 content in the Earth’s atmosphere, which is highly dependent on anthropogenic emissions of CO2, quality of emission estimation should be improved. Advanced experiment-based methods of the CO2 anthropogenic emission estimation are built on solution of an inverse problem using highly-accurate measurements of CO2 content and numerical models of transport and chemistry in the atmosphere. The accuracy of such models greatly determines errors of the emission estimations. In a current study temporal variations of column-average CO2 content in an atmospheric layer from surface to the height of ~70–75 km (XCO2) in the Russian megapolis of St. Petersburg during Jan 2019–Mar 2020 simulated by WRF-Chem model and measured by IR Fourier-transform spectrometer Bruker EM27/SUN are compared. The research has demonstrated that the WRF-Chem model simulates well the observed temporal variation of XCO2 in the area of St. Petersburg (correlation coefficient of ~0.95). However, using CarbonTracker v2022-1 data as chemical boundary conditions, the model overestimates XCO2 relative to the observations significantly during almost the whole period of investigation – systematic difference and standard deviation of the difference are 4.2 and 1.9 ppm (1 and 0.5%). A correction of the chemical boundary conditions which is based on analysis of a relation between near-surface wind direction and XCO2 variation notably decreases the systematic difference between the modelled and observed data (almost by a factor of 2). The XCO2 variation by the observations and modelling with uncorrected chemical boundary conditions are in a better agreement during vegetation season. Probably this is related to the compensation of the systematic difference by inaccuracies in estimated biogenic contribution. Hence, the reason of the still existing mean difference between the modelled and observed data can be inaccuracies in setting chemical boundary conditions for upper troposphere and in estimating how biosphere influences CO2 content.

Geochemical Evolution of Dolomites in Thanagazi Formation of Mesoproterozoic Alwar Basin, Northwest India

The geochemistry of dolomite in part of the Thanagazi Formation in the Mesoproterozoic Alwar Basin has been studied employing major and trace elements, including rare earth elements (REEs) to understand their provenance and paleoweathering conditions. In the current study, two distinct types of dolomites were identified viz. amorphous and crystalline. Various geochemical discriminants such as SiO2 vs Al2O3 and CaO vs MgO indicate that the dolomites were originated from sedimentary sources with substantial metasomatic and biogenic contributions. Geochemical constraints from plots of Fe2O3/Al2O3 vs. Al2O3/(Al2O3+Fe2O3) and rare earth element compositions for provenance signatures suggest likely deposition of dolomites in shallow marine sedimentary environment. Based on geothermometric estimates and base metal concentrations in dolomites, it is inferred that the mixing of sediments derived from two different sources (metasomatic and biogenic) were likely responsible for the dolomitization in the Thanagazi Formation of the Mesoproterozoic Alwar Basin.

Anthropogenic and Biogenic Contributions to the Organic Composition of Coastal Submicron Sea Spray Aerosol.

The organic composition of coastal sea spray aerosol is important for both atmospheric chemistry and public health but remains poorly characterized. Coastal waters contain an organic material derived from both anthropogenic processes, such as wastewater discharge, and biological processes, including biological blooms. Here, we probe the chemical composition of the organic fraction of sea spray aerosol over the course of the 2019 SeaSCAPE mesocosm experiment, in which a phytoplankton bloom was facilitated in natural coastal water from La Jolla, California. We apply untargeted two-dimensional gas chromatography to characterize submicron nascent sea spray aerosol samples, reporting ∼750 unique organic species traced over a 19 day phytoplankton bloom experiment. Categorization and quantitative compositional analysis reveal three major findings. First, anthropogenic species made up 30% of total submicron nascent sea spray aerosol organic mass under the pre-bloom condition. Second, biological activity drove large changes within the aerosolized carbon pool, decreasing the anthropogenic mass fraction by 89% and increasing the biogenic and biologically transformed fraction by a factor of 5.6. Third, biogenic marine organics are underrepresented in mass spectral databases in comparison to marine organic pollutants, with more than twice as much biogenic aerosol mass attributable to unlisted compounds.

Characteristics of VOC Composition at Urban and Suburban Sites of New Delhi, India in Winter

AbstractSimultaneous measurements of volatile organic compounds (VOCs) using two PTR‐TOF‐MS instruments were conducted at urban and suburban sites of New Delhi during the winter of 2018. The time series of VOC mixing ratios show substantial variations mainly influenced by local emissions and meteorological conditions. Mixing ratios of methanol (∼28 ppbv), acetaldehyde (7.7 ppbv), acetone (10.6 ppbv), isoprene (2.8 ppbv) and monoterpenes (0.84 ppbv) at the suburban site were higher than those at the urban site, while levels of aromatic VOCs were almost similar. The strong nighttime correlations of isoprene and monoterpenes with CO and benzene at the urban site indicate their predominant anthropogenic origin. Higher emission ratios of ∆VOCs/∆CO and ∆VOCs/∆benzene than those reported for vehicular exhaust suggest the contributions of other sources. In addition to vehicular emissions, episodes of biomass burning, industrial plumes and aged air strongly influenced the levels of VOCs at the suburban site. Despite the predominant primary anthropogenic emissions, the higher daytime enhancements of OVOCs/CO ratios indicate additional contributions of OVOCs from secondary/biogenic sources. The secondary formation of OVOCs in moderately aged air masses was noticeable at the suburban site. Using the source‐tracer‐ratio method, the estimated biogenic contributions of isoprene (71%) and acetone (65%) during daytime at the suburban site were significantly higher than those for the urban site. The photochemical box model simulations suggest that daytime ozone formation was under the VOC‐limited regime. The present study highlights the impact of different emission sources, photochemical processes and meteorological conditions on the composition and concentration of VOCs in the Delhi region.

Brown carbon from biomass burning imposes strong circum-Arctic warming

Brown carbon from biomass burning imposes strong circum-Arctic warming

Assessment of Total Petroleum Hydrocarbons and Polycyclic Aromatic Hydrocarbons in Wastewater from Selected Flow Stations in Agbada II, Rivers State

Aims: This study evaluates total petroleum hydrocarbon (TPH) and polycyclic hydrocarbons (PAHs) concentrations in wastewaters from three locations of the oil-producing flow station in Rivers State.
 Study Design: By experiment and the results obtained by analytical means.
 Place and Duration of Study: This work was conducted at the Department of Industrial Chemistry/Petrochemical Technology, School of Science and Laboratory Technology, University of Port Harcourt, Choba, Rivers State, Nigeria between February and August, 2021.
 Methodology: The evaluation was done using gas chromatography-Flame Ionization Detector (GC-FID), and Gas Chromatography-Mass Spectrometer Detector (GC-MSD).
 Results: Results obtained showed low levels of total petroleum hydrocarbons ranging from 0.051, 0.119, and 0.07 mg/l and 0.01, 0.06, and < 0.01 mg/l for polycyclic aromatic hydrocarbons for the three locations, respectively. The results also revealed that the concentrations of the total petroleum hydrocarbons of the samples from the three locations were highest at carbon atom 17 suggesting a biogenic contribution of organic matter. The chromatographs obtained gave evidence that the nature of the contamination was minimally crude oil, because crude oil normally distributes in broad range, as observed in the locations samples as against the narrower carbon range of C8 to C40 characteristics of refined products. The pristane/phytane ratios, which were 0.925, 0.891 and 0.372 for the three samples, depicted an oxygenated environment. The C17/pristane ratios (39.53, 38.93, and 31.48) for all three locations revealed that the wastewaters were slightly weathered. The low concentrations as well as absence of high molecular weight polycyclic aromatic hydrocarbons and higher concentrations of low molecular weight polycyclic aromatic hydrocarbons support the petrogenity of the wastewaters. 
 The phenanthrene/anthracene ratios (1.26, 0, and 0) for the three samples confirm the nature of the wastewaters. In addition, the absence of benzo(a)anthracene to chrysene ratio for all three samples point to proper treatment of the wastewaters.
 Conclusion: From this study, the level of total petroleum hydrocarbons (TPH) and polycyclic hydrocarbons (PAHs) obtained from all the samples were lower than the maximum recommended levels by the Department of Petroleum Resources (DPR). This study recommends constant monitoring in the total petroleum hydrocarbons and polycyclic hydrocarbons concentrations because even at its low concentrations can be injurious to health of the people residing within the facility and beyond.

Measurement report: Source apportionment of volatile organic compounds at the remote high-altitude Maïdo observatory

Abstract. We present a source apportionment study of a near-continuous 2-year dataset of volatile organic compounds (VOCs), recorded between October 2017 and November 2019 with a quadrupole-based high-sensitivity proton-transfer-reaction mass-spectrometry (hs-PTR-MS) instrument deployed at the Maïdo observatory (21.1∘ S, 55.4∘ E, 2160 m altitude). The observatory is located on La Réunion island in the southwest Indian Ocean. We discuss seasonal and diel profiles of six key VOC species unequivocally linked to specific sources – acetonitrile (CH3CN), isoprene (C5H8), isoprene oxidation products (Iox), benzene (C6H6), C8-aromatic compounds (C8H10), and dimethyl sulfide (DMS). The data are analyzed using the positive matrix factorization (PMF) method and back-trajectory calculations based on the Lagrangian mesoscale transport model FLEXPART-AROME to identify the impact of different sources on air masses sampled at the observatory. As opposed to the biomass burning tracer CH3CN, which does not exhibit a typical diel pattern consistently throughout the dataset, we identify pronounced diel profiles with a daytime maximum for the biogenic (C5H8 and Iox) and anthropogenic (C6H6, C8H10) tracers. The marine tracer DMS generally displays a daytime maximum except for the austral winter when the difference between daytime and nighttime mixing ratios vanishes. Four factors were identified by the PMF: background/biomass burning, anthropogenic, primary biogenic, and secondary biogenic. Despite human activity being concentrated in a few coastal areas, the PMF results indicate that the anthropogenic source factor is the dominant contributor to the VOC load (38 %), followed by the background/biomass burning source factor originating in the free troposphere (33 %), and by the primary (15 %) and secondary biogenic (14 %) source factors. FLEXPART-AROME simulations showed that the observatory was most sensitive to anthropogenic emissions west of Maïdo while the strongest biogenic contributions coincided with air masses passing over the northeastern part of La Réunion. At night, the observatory is often located in the free troposphere, while during the day, the measurements are influenced by mesoscale sources. Interquartile ranges of nighttime 30 min average mixing ratios of methanol (CH3OH), CH3CN, acetaldehyde (CH3CHO), formic acid (HCOOH), acetone (CH3COCH3), acetic acid (CH3COOH), and methyl ethyl ketone (MEK), representative for the atmospheric composition of the free troposphere, were found to be 525–887, 79–110, 61–101, 172–335, 259–379, 64–164, and 11–21 pptv, respectively.

Benthic jellyfish dominate water mixing in mangrove ecosystems

Water mixing is a critical mechanism in marine habitats that governs many important processes, including nutrient transport. Physical mechanisms, such as winds or tides, are primarily responsible for mixing effects in shallow coastal systems, but the sheltered habitats adjacent to mangroves experience very low turbulence and vertical mixing. The significance of biogenic mixing in pelagic habitats has been investigated but remains unclear. In this study, we show that the upside-down jellyfish Cassiopea sp. plays a significant role with respect to biogenic contributions to water column mixing within its shallow natural habitat ([Formula: see text] m deep). The mixing contribution was determined by high-resolution flow velocimetry methods in both the laboratory and the natural environment. We demonstrate that Cassiopea sp. continuously pump water from the benthos upward in a vertical jet with flow velocities on the scale of centimeters per second. The volumetric flow rate was calculated to be 212 L⋅h-1 for average-sized animals (8.6 cm bell diameter), which translates to turnover of the entire water column every 15 min for a median population density (29 animals per m2). In addition, we found Cassiopea sp. are capable of releasing porewater into the water column at an average rate of 2.64 mL⋅h-1 per individual. The release of nutrient-rich benthic porewater combined with strong contributions to water column mixing suggests a role for Cassiopea sp. as an ecosystem engineer in mangrove habitats.

Multi isotope systematics of precipitation to trace the sources of air pollutants in Seoul, Korea

Multiple sulfur (δ34Ssulfate, Δ33Ssulfate, & Δ36Ssulfate), nitrogen and oxygen (δ15Nnitrate & δ18Onitrate) and strontium (87Sr/86Sr) isotope compositions of precipitation collected from Seoul, South Korea were analyzed to study the sources, transportation and deposition of air pollutants in East Asia. The δ34Ssulfate values (from 1.9 to 14.6‰ with a median of 4.7‰) and the δ15Nnitrate values (from −2.0 to 13.3‰ with a median of 1.0‰) suggest that fossil fuel use (emission from coal combustion and vehicle exhaust) is a predominant source for sulfur and nitrogen, but other natural sources including biogenic contributions of DMS also add to their total budget. The seasonal variations are observed in δ34Ssulfate and δ15Nnitrate values (both higher in winter season), which is likely to result from the increase of coal use for domestic heating in China. The δ18Onitrate values also varied seasonally depending on the NOx oxidation pathway, being about 20‰ higher in winter than in summer season. The Δ33Ssulfate and Δ36Ssulfate values are not anomalous, showing the absence of MIF signals in precipitation of Seoul. The 87Sr/86Sr ratio of the precipitation samples range from 0.70988 to 0.71487 with a median of 0.71073, indicating the influence of at least three end-member (silicate dust, carbonate dust and anthropogenic emission). Ionic ratios such as (K++NH4+)/(Ca2++Mg2+) and Cl−/Na+ suggest the overwhelming effect of anthropogenic input rather than carbonate dust on the end-member with lower 87Sr/86Sr ratios.

Occurrence and cycle of dimethyl sulfide in the western Pacific Ocean

AbstractOceanic production and occurrence of dimethyl sulfide (DMS) and its subsequent ventilation to the atmosphere significantly contribute to the global sulfur cycle and impact the climate regulation. Spatial distributions of DMS, dimethylsulfoniopropionate (DMSP, precursor of DMS), and dimethyl sulfoxide (DMSO, oxidation product of DMS), production and removal processes of DMS (including biological production, microbial consumption, photo‐degradation, and sea‐to‐air exchange), and biogenic contributions to the atmospheric sulfate burden were simultaneously studied in the western Pacific Ocean during winter. Sea surface DMS, DMSP, and DMSO were strongly correlated and had similar distribution patterns. The DMS photo‐degradation efficiency ratio (normalized using incident photon flux density) for ultraviolet B radiation (UVB): ultraviolet A radiation (UVA): photosynthetically active radiation (PAR) was 391: 36: 1. However, considering the solar spectral composition, the actual contributions of UVB, UVA, and PAR to DMS photo‐degradation in surface waters were 40.6% ± 10.7%, 41.2% ± 15.6%, and 18.2% ± 7.2%, respectively. When integrated across the entire mixed layer, UVA and PAR became the dominant drivers, accounting for 45.2% ± 18.0% and 38.0% ± 17.3% of DMS photo‐degradation, respectively, as UVB was significantly attenuated in seawater. The DMS budget of the entire mixed layer indicated that microbial consumption, photo‐degradation, and ventilation accounted for about 74.3% ± 11.9%, 19.3% ± 9.3%, and 6.5% ± 4.0% of total DMS removal, respectively. Even if ventilation was a minor DMS removal pathway, DMS emissions still contributed approximately 45.2% ± 25.6% of the atmospheric non‐sea‐salt sulfate burden over the western Pacific Ocean.