Missing Source Research Articles

Atmospheric Bases-Enhanced Iodic Acid Nucleation: Altitude-Dependent Characteristics and Molecular Mechanisms.

Iodic acid (IA), the key driver of marine aerosols, is widely detected within the gas and particle phases in the marine boundary layer (MBL) and even the free troposphere (FT). Although atmospheric bases like dimethylamine (DMA) and ammonia (NH3) can enhance IA particles formation, their different efficiencies and spatial distributions make the dominant base-stabilization mechanisms of forming IA particles unclear. Herein, we investigated the IA-DMA-NH3 nucleation system through quantum chemical calculations at the DLPNO-CCSD(T)/aug-cc-pVTZ(-PP)//ωB97X-D/6-311++G(3df,3pd) + aug-cc-pVTZ-PP level of theory and cluster dynamics simulations. We provide molecular-level evidence that DMA and NH3 can jointly stabilize the IA clusters. The formation rates of IA clusters initially decline before rising from the MBL to the FT, owing to variations in mechanism. In the MBL, IA-DMA nucleation predominates, while the contribution of IA-DMA-NH3 synergistic nucleation cannot be overlooked in polar and NH3-polluted regions. In the lower FT, IA-DMA-NH3 nucleation prevails, whereas in the upper FT, IA-NH3 nucleation dominates. The efficiency of IA-DMA-NH3 nucleation is comparable to that of IA-iodous acid nucleation in the MBL and sulfuric acid-NH3 nucleation in the FT. Hence, the IA-DMA-NH3 mechanism holds promise for revealing the missing sources of tropospheric IA particles.

A light - Driven acidic positive feedback mechanism of sulfate formation

As the main source of atmospheric sulfate aerosol, the aqueous-phase oxidation of SO2 has been of great concern. Traditionally, the aqueous-phase oxidation of SO2 is considered a consumption process of atmospheric oxidation capacity; however, we report here that •OH radicals and other reactive oxygen species (ROS) can be generated in the photochemical reactions of bulk HSO3− solution. This •OH production pathway results in the fast sulfate formation in the photooxidation of dissolved SO2. The photochemical process is determined to be pH-dependent in which sulfate formation is promoted by decreasing pH. Hence, a light - driven acidic positive feedback mechanism is proposed that the oxidation of dissolved SO2 and the formation of •OH radicals have a synergistic promoting effect. These results indicate that the photochemistry of dissolved SO2 could be a missing source of aqueous •OH radicals as well as sulfate at regional to global scales.

Identifying and characterizing missing source orogens for syn-orogenic basins based on detrital accessory mineral U-Pb geochronology and trace element geochemistry

Abstract Identifying source orogens for syn-orogenic sediments in dispersed fragments of a supercontinent provides key information on the tectonic evolution of the orogens involved in supercontinent assembly and on paleogeographic reconstruction. An approach using U-Pb geochronology and trace elements of multiple detrital minerals including zircon, rutile, apatite, and monazite has major advantages over detrital zircon studies alone. Application of this multi-pronged approach to Ediacaran and Cambrian clastic sedimentary rocks from the West Cathaysia terrane of the South China block demonstrates that these rocks were deposited in two distinct, but overlapping, syn-orogenic basins related to the assembly of eastern Gondwana. The Ediacaran rocks have detritus likely sourced from the Paterson-Petermann orogen (PPO) in Australia, and the dominant 650–600 Ma populations and trace element compositions of detrital rutile and apatite indicate a significant Ediacaran thermal and high-pressure metamorphic event in the orogen. The appearance of Cambrian and Tonian detrital rutile and apatite populations in the Cambrian rocks indicates derivation from a different source orogen characterized by multiple thermal events, most likely the Kuunga-Pinjarra orogen (KPO). Our data suggest that West Cathaysia was located adjacent to both the PPO and the KPO and support the hypothesis that the PPO was a collisional, rather than a long-lived post-Grenvillian intraplate, orogen. Our data also suggest a poly-metamorphic history for the poorly preserved northern part of the KPO and a larger expanse of Greater India.

Enhanced nitrous acid (HONO) formation via NO2 uptake and its potential contribution to heavy haze formation during wintertime

A full understanding of the sources of atmospheric nitrous acid (HONO) in the polluted urban atmosphere remains a challenge. In this study, ambient HONO and relevant species were measured during January 2019 at an urban site in Beijing, China, and a budget analysis of HONO was conducted using a box model combined with field observations. Large nighttime “missing sources” of HONO were identified on heavily polluted days based on traditional sources, which had a significant correlation with the relative humidity, ammonia (NH3), and aerosol surface area, and the promotional effect of NH3 for nitrogen dioxide (NO2) uptake on the wet aerosol surface was discussed. Then, an updated parameterization scheme for quantifying the enhanced heterogeneous reactions of NO2 on aerosol surfaces is proposed, and the missing nighttime sources of HONO could be substantially compensated after the new scheme was incorporated. Further evaluation on the contributions of HONO to hydroxyl radicals was conducted, and the authors found that the photolysis of HONO played a dominant role in the primary OH production on the polluted days (78%–90%). The study reveals great potential of an NH3-enhanced uptake coefficient of NO2 on the aerosol surface in the nocturnal HONO budget, and highlights the significance of HONO in the strong atmospheric oxidation capability during episodes with a heavily polluted atmosphere.摘要本文研究了重污染过程中气态亚硝酸 (HONO) 的关键来源并基于化学箱模型对其源汇过程进行了闭合分析. 结果显示, 现有的HONO 源汇机制并不能解释观测期间出现的高HONO事件, 尤其是重污染过程夜间存在大量的HONO "未知源". 本文提出了一套新的HONO 源汇参数化方案, 可以较好的模拟观测期间HONO日间和夜间来源, 并进一步评估了HONO 对羟基自由基 (OH) 的贡献, 发现 HONO 光解主导了重污染天OH生成 (78%–90%). 研究结果揭示了华北城市富氨大气环境促进 NO2在气溶胶表面的摄取和非均相反应进而主导了夜间HONO生成, 凸显了HONO化学对于重污染过程维持大气氧化能力的重要作用.

Reactive aldehyde chemistry explains the missing source of hydroxyl radicals

Hydroxyl radicals (OH) determine the tropospheric self-cleansing capacity, thus regulating air quality and climate. However, the state-of-the-art mechanisms still underestimate OH at low nitrogen oxide and high volatile organic compound regimes even considering the latest isoprene chemistry. Here we propose that the reactive aldehyde chemistry, especially the autoxidation of carbonyl organic peroxy radicals (R(CO)O2) derived from higher aldehydes, is a noteworthy OH regeneration mechanism that overwhelms the contribution of the isoprene autoxidation, the latter has been proved to largely contribute to the missing OH source under high isoprene condition. As diagnosed by the quantum chemical calculations, the R(CO)O2 radicals undergo fast H-migration to produce unsaturated hydroperoxyl-carbonyls that generate OH through rapid photolysis. This chemistry could explain almost all unknown OH sources in areas rich in both natural and anthropogenic emissions in the warm seasons, and may increasingly impact the global self-cleansing capacity in a future low nitrogen oxide society under carbon neutrality scenarios.

Variable stars in galactic globular clusters. I. The population of RR Lyrae stars

We present a comprehensive catalog of $2824$ RR Lyrae stars (RRLs) residing in $115$ Galactic globular clusters (GCs). Our catalog includes 1594 fundamental-mode (RRab), 824 first-overtone (RRc), and 28 double-mode (RRd) RRLs, as well as 378 RRLs of an unknown pulsation mode. We cross-matched 481\,349 RRLs reported in the third data release (DR3) of the ESA mission and the literature to 170 known GCs. Membership probabilities were computed as the products of a position and shape-dependent prior and a likelihood was computed using parallaxes, proper motions, and, where available, radial velocities from Membership likelihoods of RRLs were computed by comparing cluster average parameters based on known member stars and the cross-matched RRLs. We determined empirical RRL instability strip (IS) boundaries based on our catalog and detected three new cluster RRLs inside this region via their excess $G-$band photometric uncertainties. We find that $77<!PCT!>$ of RRLs in GCs are included in the DR3 Specific Object Study, and $82<!PCT!>$ were classified as RRLs by the DR3 classifier, with the majority of the missing sources being located at the crowded GC centers. Surprisingly, we find that $25<!PCT!>$ of cluster member stars located within the empirical IS are not RRLs and appear to be non-variable. Additionally, we find that $80<!PCT!>$ of RRab, $84<!PCT!>$ of RRc, and $100<!PCT!>$ of the RRd stars are located within theoretical IS boundaries predicted using MESA models with $Z=0.0003$, $M=0.7$ \(M_ and $Y=0.290$. Unexpectedly, a higher $Y=0.357$ is required to fully match the location of RRc stars, and lower $Y=0.220$ is needed to match the location of RRab stars. Lastly, our catalog does not exhibit an Oosterhoff dichotomy, with at least 22 GCs located inside the Oosterhoff "gap," which is close to the mode of the distribution of mean RRL periods in GCs.

Coarse particles compensate for missing daytime sources of nitrous acid and enhance atmospheric oxidation capacity in a coastal atmosphere

Large missing sources of daytime atmospheric nitrous acid (HONO), a vital source of hydroxyl radicals (OH) through its photolysis, frequently exist in global coastal regions. In this study, ambient HONO and relevant species were measured at a coastal site in the Pearl River Delta (PRD), China, during October 2019. Relatively high concentrations (0.32 ± 0.19 ppbv) and daytime peaks at approximately 13:00 of HONO were observed, and HONO photolysis was found to be the dominant (55.5 %) source of the primary OH production. A budget analysis of HONO based on traditional sources suggested large unknown sources during the daytime (66.4 %), which had a significant correlation with the mass of coarse particles (PM2.5–10) and photolysis frequency (J(NO2)). When incorporating photolysis of the abundant nitrate measured in coarse particles with a reasonable enhancement factor relative to fine particles due to favorable aerosol conditions, the missing daytime sources of HONO could be fully compensated by coarse particles serving as the largest source at this coastal site. Our study revealed great potential of coarse particles as a strong daytime HONO source, which has been ignored before but can efficiently promote NOx recycling and thus significantly enhance atmospheric oxidation capacity.

Exploring the HONO source during the COVID-19 pandemic in a megacity in China

HONO is a critical precursor of •OH, but its sources are controversial due to its complex formation mechanism. This study conducted comprehensive observations in Zhengzhou from April 26 to May 11, 2022. Low NOx concentrations were observed during the Covid epidemic period (EP) (10.4 ± 3.0 ppb), compared to the pre-epidemic period (PEP) (12.5 ± 3.8 ppb). The mean HONO concentration during EP (0.53 ± 0.34 ppb) was 0.09 ppb lower than that during PEP (0.62 ± 0.53 ppb). The decrease in HONO concentration during EP came mainly at night due to the reduction in the direct emission (Pemi) (0.03 ppb/hr), the homogeneous reaction between •OH and NO (POH+NO) (0.02 ppb/hr), and the heterogeneous conversion of NO2 on the ground (0.01 ppb/hr). Notably, there was no significant change in daytime HONO concentration. The daytime HONO budget indicated that the primary HONO sources during PEP were the nitrate photolysis (Pnitrate), followed by the POH+NO, Pemi, the photo-enhanced reaction of NO2 on the ground (Pground+hv) and aerosol surface (Paerosol+hv). The primary HONO sources were Pnitrate, POH+NO, Pemi, and Paerosol+hv during EP, respectively. The missing source has a high correlation with solar radiation, there might be other photo-related HONO sources or the contributions of photosensitized reactions were underestimated. In the extremely underestimated cases, HONO production rates from the Pnitrate, Pground+hv, and Paerosol+hv increased by 0.17, 0.10, and 0.10 ppb/hr during PEP, 0.23, 0.13, and 0.16 ppb/hr during EP, and Pnitrate was still the primary source during both PEP and EP.

Comparing Microbial Source Tracking Methods for Precision and Reliability

Microbial source tracking is a valuable tool in forensic science, specifically in the analysis of trace evidence. Numerous tools have been developed to estimate the proportion of different contamination sources within a mixture. In this study, we evaluate the accuracy of various source tracking methods using datasets from microbiome studies. In addition to assessing source tracking methods, we also incorporate two widely used cell type deconvolution methods, namely EPIC and PREDE, which are designed to identify missing cell types in a given dataset. Furthermore, we investigate the effectiveness of combined methods by integrating RAD, a source tracking method aimed at filtering out unimportant sources, with either EPIC or PREDE for enhanced accuracy in both source tracking and cell type deconvolution. This research represents a pioneering effort to examine the application of cell type deconvolution methods in source tracking and vice versa. Particularly noteworthy is our focus on scenarios involving missing sources or cell types in the reference data, shedding light on the intricate interplay between these two analytical domains.

The complex relationship between precipitation and productivity in drylands

Abstract Drylands provide multiple essential services to human society, and dryland vegetation is one of the foundations of these services. There is a paradox, however, in the vegetation productivity–precipitation relationship in drylands. Although water is the most limiting resource in these systems, a strong relationship between precipitation and productivity does not always occur. Such a paradox affects our understanding of dryland vegetation dynamics and hinders our capacity to predict dryland vegetation responses under future climates. In this perspective, we examine the possible causes of the dryland precipitation–productivity paradox. We argue that the underlying reasons depend on the location and scale of the study. Sometimes multiple factors may interact, resulting in a less significant relationship between vegetation growth and water availability. This means that when we observe a poor correlation between vegetation growth and water availability, there are potentially missing sources of water input or a lack of consideration of other important processes. The paradox could also be related to the inaccurate measurement of vegetation productivity and water availability indicators. Incorporating these complexities into predictive models will help us better understand the complex relationship between water availability and dryland ecosystem processes and improve our ability to predict how these ecosystems will respond to the multiple facets of climate change.

Evaluation of the behavior of BTEX at Beijing and Seoul in winter and summer using observations and 3-D modeling

Aromatic volatile organic compounds (VOCs) including benzene, toluene, ethylbenzene, xylene, and trimethylbenzene (BTEX) are known to contribute the most to the formation of ozone and secondary organic aerosols (SOA) in an urban atmosphere and their representation in chemical transport models (CTM) is still uncertain. In this study, we evaluated the model representation of BTEX concentrations and their seasonal difference at Beijing and Seoul using the GEOS-Chem CTM and ground observations from the Fine particle Research Initiative in East Asia considering National Differences (FRIEND) project in winter and summer. The model captured different levels of observed BTEX at Beijing and Seoul, where benzene (BENZ) was comparable and toluene + ethylbenzene (TOLU) and xylenes + trimethylbenzenes (XYLE) were higher at Seoul. The observed seasonal variations of BTEX were similar at both sites, with benzene being higher in winter and TOLU and XYLE being higher in summer. However, the magnitude and seasonal variation of TOLU at Seoul and BENZ at Beijing were not reproduced by the model. TOLU was underestimated in both seasons at Seoul especially in summer due to the underestimation of emission rates and evaporative emission being not included in the current emission inventory. At Beijing, BENZ was underestimated especially in winter and showed no seasonal variation which was different from the observations. Underestimated benzene emission rates or missing sources of it cause discrepancies between observed and modeled benzene concentrations at Beijing.

Unsupervised Multimodal Anomaly Detection With Missing Sources for Liquid Rocket Engine.

To achieve reliable and automatic anomaly detection (AD) for large equipment such as liquid rocket engine (LRE), multisource data are commonly manipulated in deep learning pipelines. However, current AD methods mainly aim at single source or single modality, whereas existing multimodal methods cannot effectively cope with a common issue, modality incompleteness. To this end, we propose an unsupervised multimodal method for AD with missing sources in LRE system. The proposed method handles intramodality fusion, intermodality fusion, and decision fusion in a unified framework composed of multiple deep autoencoders (AEs) and a skip-connected AE. Specifically, the first module restores missing sources to construct a complete modality, thus advancing the secondary reconstruction. Different from vanilla reconstruction-based methods, the proposed method minimizes reconstruction loss and meanwhile maximizes the dissimilarity of representations in two latent spaces. Utilizing reconstruction errors and latent representation discrepancy, the anomaly score is acquired. At decision level, the model performance can be further enhanced via anomaly score fusion. To demonstrate the effectiveness, extensive experiments are carried out on multivariate time-series data from static ignition of several LREs. The results indicate the superiority and potential of the proposed method for AD with missing sources for LRE.

Submarine Groundwater Discharge Exceeds River Inputs as a Source of Nutrients to the Great Barrier Reef.

Rivers are often assumed to be the main source of nutrients triggering eutrophication in the Great Barrier Reef (GBR). However, existing nutrient budgets suggest a major missing source of nitrogen and phosphorus sustaining primary production. Here, we used radium isotopes to resolve submarine groundwater discharge (SGD)-derived, shelf-scale nutrient inputs to the GBR. The total SGD was ∼10-15 times greater than average river inputs, with nearshore groundwater discharge accounting for ∼30% of this. Total SGD accounted for >30% of all known dissolved inorganic N and >60% of inorganic P inputs and exceeded regional river inputs. However, SGD was only a small proportion of the nutrients necessary to sustain primary productivity, suggesting that internal recycling processes still dominate the nutrient budget. With millions of dollars spent managing surface water nutrient inputs to reef systems globally, we argue for a shift in the focus of management to safeguard reefs from the impacts of excess nutrients.

Intense methane diffusive emissions in eutrophic urban lakes, Central China

Urban lakes are hotspots of methane (CH4) emissions. Yet, actual field measurements of CH4 in these lakes are rather limited and our understanding of CH4 response to urban lake eutrophication is still incomplete. In this study, we measured dissolved CH4 concentrations and quantified CH4 diffusion from four urban lakes in subtropical China during wet and dry seasons. We found that these lakes were constantly CH4-saturated, contributing the greenhouse gas (GHG) to the atmosphere. Nutrient enrichment significantly increased CH4 concentrations and diffusive fluxes. Average CH4 flux rate in the highly-eutrophic lake zones (4.18 ± 7.68 mmol m−2 d−1) was significantly higher than those in the mesotrophic (0.19 ± 0.18 mmol m−2 d−1) and lightly/moderately-eutrophic zones (0.72 ± 2.22 mmol m−2 d−1). Seasonally, CH4 concentrations and fluxes were significantly higher in the wet season than in the dry season in the mesotrophic and the lightly/moderately-eutrophic lake zones, but an inverse pattern existed in the highly-eutrophic lake zones. CH4 concentrations and fluxes increased with elevated levels of nitrogen, phosphorus and dissolved organic carbon (DOC). The accumulation of nutrients provided autochthonous substrate for methanogenesis, indicated by a negative correlation between CH4 and the C:N ratio. Ammonium-nitrogen (NH4+-N) was the best predictor for spatial fluctuation of CH4 concentrations and diffusive fluxes in the mesotrophic and the lightly/moderately-eutrophic lake zones, while total nitrogen (TN) and total phosphorus (TP) levels showed the highest predictability in the highly-eutrophic lake zones. Based on the findings, we conclude that nutrient enrichment in urban lakes can largely increase CH4 diffusion, and that urban sewage inflow is a key concern for eutrophication boosting CH4 production and diffusive emission. Furthermore, our study reveals that small urban lakes may be an important missing source of GHG emissions in the global C accounting, and that the ratio of littoral-to-pelagic zones can be important for predicting lake-scale estimation of CH4 emission.

Highly Depleted Alkali Metals in Jupiter’s Deep Atmosphere

Water and ammonia vapors are known to be the major sources of spectral absorption at pressure levels observed by the microwave radiometer (MWR) on Juno. However, the brightness temperatures and limb darkening observed by the MWR at its longest-wavelength channel of 50 cm (600 MHz) in the first nine perijove passes indicate the existence of an additional source of opacity in the deep atmosphere of Jupiter (pressures beyond 100 bar). The absorption properties of ammonia and water vapor, and their relative abundances in Jupiter’s atmosphere, do not provide sufficient opacity in the deep atmosphere to explain the 600 MHz channel observation. Here we show that free electrons due to the ionization of alkali metals, i.e., sodium and potassium, with subsolar metallicity, [M/H] (log-based 10 relative concentration to solar) in the range of [M/H] = −2 to [M/H] = −5, can provide the missing source of opacity in the deep atmosphere. If the alkali metals are not the source of additional opacity in the MWR data, then their metallicity at 1000 bars can only be even lower. This upper bound of −2 on the metallicity of the alkali metals contrasts with the other heavy elements—C, N, S, Ar, Kr, and Xe—that are all enriched relative to their solar abundances, having a metallicity of approximately +0.5.

Mixing Models With Multiple, Overlapping, or Incomplete End‐Members, Quantified Using Time Series of a Single Tracer

AbstractMixing models are used throughout earth and environmental science to quantify the relative contributions of sources to mixtures, based on chemical or isotopic tracers. Often, however, some end‐members are missing or their tracer distributions overlap, precluding the use of conventional mixing models. Here I show how these constraints can be overcome by exploiting the information contained in tracer time‐series fluctuations. This approach, ensemble end‐member mixing analysis (EEMMA), can potentially quantify many sources using a single tracer, even if their mean concentrations are indistinguishable. EEMMA can also quantify source contributions when some sources are unknown, and even infer the tracer time series of a missing source. Benchmark tests with synthetic data verify the reliability of this approach, thus expanding the range of mixing models that can be quantified using tracer time series. An R script is provided for the necessary calculations, including error propagation.

Conformer-Dependent Chemistry: Experimental Product Branching of the Vinyl Alcohol + OH + O2 Reaction

The concentration of formic acid in Earth's troposphere is underestimated by detailed chemical models compared to field observations. Phototautomerization of acetaldehyde to its less stable tautomer vinyl alcohol, followed by the OH-initiated oxidation of vinyl alcohol, has been proposed as a missing source of formic acid that improves the agreement between models and field measurements. Theoretical investigations of the OH + vinyl alcohol reaction in excess O2 conclude that OH addition to the α carbon of vinyl alcohol produces formaldehyde + formic acid + OH, whereas OH addition to the β site leads to glycoaldehyde + HO2. Furthermore, these studies predict that the conformeric structure of vinyl alcohol controls the reaction pathway, with the anti-conformer of vinyl alcohol promoting α OH addition, whereas the syn-conformer promotes β addition. However, the two theoretical studies reach different conclusions regarding which set of products dominate. We studied this reaction using time-resolved multiplexed photoionization mass spectrometry to quantify the product branching fractions. Our results, supported by a detailed kinetic model, conclude that the glycoaldehyde product channel (arising mostly from syn-vinyl alcohol) dominates over formic acid production with a 3.6:1.0 branching ratio. This result supports the conclusion of Lei et al. that conformer-dependent hydrogen bonding at the transition state for OH-addition controls the reaction outcome. As a result, tropospheric oxidation of vinyl alcohol creates less formic acid than recently thought, increasing again the discrepancy between models and field observations of Earth's formic acid budget.

Chlorinated solvents source identification by nonlinear optimization method.

In this work, chloride ions were used as conservative tracers and supplemented with conservative amounts of chloroethenes (PCE, TCE, Cis-DCE, 1,1-DCE), chloroethanes (1,1,1-TCA, 1,1-DCA), and the carbon isotope ratios of certain compounds, the most representative on the sites studied, which is a novelty compared to the optimization methods developed in the scientific literature so far. A location of the potential missing sources is then proposed in view of the balances of the calculated mixing fractions. A test of the influence of measurement errors on the results shows that the uncertainties in the calculation of the mixture fractions are less than 11%, indicating that the source identification method developed is a robust tool for identifying sources of chlorinated solvents in groundwater.

Dynamics of estrogenic activity in an urban river receiving wastewater effluents: effect-based measurements with CALUX

Estrogenic substances (ES) in an urban river Zenne (BE) dominated by wastewater effluents were assessed over the course of one year. To measure the bioequivalent (BEQ) 17 β-estradiol (E2) concentrations of ES, the biological effect-based methodology - the Chemical-Activated LUciferase gene eXpression (CALUX) bioassay was used. Daily water discharges were collected from January 2015 to February 2016 at or near the sampling stations in the Brussels Capital Region. An annual water budget shows that approximately 50% of the Zenne River flow downstream is from wastewater effluent. The estrogenic activity and yearly average ES load in influents and effluents of wastewater treatment plants (WWTPs) located in the North and South, combined sewer overflows (CSOs) and the Zenne River, were assessed for upstream and downstream of two WWTPs of Brussels. Both WWTPs with activated sludge treatment remove more than 90% of the ES. The influent concentrations of ES at the South and North WWTPs ranged from 30-359 and 18-55 ng E2 eq./L, respectively. The effluent concentrations of ES ranged from 1.0-2.1 and 1.1-6.6 ng E2 eq./L at WWTP-S and -N, respectively. The yearly average ES loads were 0.05-0.14 and 0.39-1.5 g E2 eq./d for WWTP-S and -N, respectively. The temporal variation of E2-eq concentrations at the river stations Z3 and Z5 (upstream) ranged from 1 to 2 ng E2 eq./L, while the ES activity at sites Z9 and Z11 (downstream) varied from 2-17 ng E2 eq./L and from 1-8 ng/L ng E2 eq./L, respectively. The relative ES loads to the Zenne River are as follows: WWTPs (31%), CSOs (27%), upstream Zenne (15%), a missing source (14%), and local tributaries (13%). ES in the Zenne River behave in a pseudo-persistent manner because of continuous input from the WWTPs and slow degradation in the 18 km river stretch. The BEQ concentration of E2 exceeds the EU environmental quality standards (EQS) of 0.4 ng E2/L throughout the Zenne River.

The critical role of dimethylamine in the rapid formation of iodic acid particles in marine areas

Marine new particle formation (NPF) can affect cloud condensation nuclei (CCN) in the global atmosphere. Recently, iodic acid (IA) has been identified as a critical driver for marine NPF. However, atmospheric observations of IA cannot be associated with predicted particle formation rates. Given the complexity of atmospheric components, other species may promote IA particle formation. As an efficient stabilizer for acidic precursors, dimethylamine (DMA) has a wide distribution over the oceans. Hence, we investigated the nucleation process of DMA and IA under different atmospheric conditions and uncovered the corresponding nucleating mechanism using a quantum chemical approach and Atmospheric Cluster Dynamics Code (ACDC). The findings show that DMA can structurally stabilize IA via hydrogen and halogen bonds, and the clustering process is energy barrierless. Moreover, DMA can enhance the formation rate of IA clusters by five orders of magnitude, and its efficiency in promoting IA cluster formation is much higher than that of NH3. Compared to the nucleation via sequential addition of IA, the IA-DMA nucleation plays a more dominant role in nucleation kinetic. Thus, the effect of DMA on enhancing IA cluster stability and formation rate cannot be ignored, especially in the regions near the source of IA and DMA emissions. Broadly, the proposed IA-DMA nucleation mechanism may help to explain some missing sources of particles and, thus intensive marine NPF events.