Oceans dominate emissions of dimethyl sulfide (DMS), the major natural sulfur source. DMS is important for the formation of non-sea salt sulfate (nss-SO₄2−) aerosols and secondary particulate matter ...over oceans and thus, significantly influence global climate. The mechanism of DMS oxidation has accordingly been investigated in several different model studies in the past. However, these studies had restricted oxidation mechanisms that mostly underrepresented important aqueous-phase chemical processes. These neglected but highly effective processes strongly impact direct product yields of DMS oxidation, thereby affecting the climatic influence of aerosols. To address these shortfalls, an extensive multiphase DMS chemistry mechanism, the Chemical Aqueous Phase Radical Mechanism DMS Module 1.0, was developed and used in detailed model investigations of multiphase DMS chemistry in the marine boundary layer. The performed model studies confirmed the importance of aqueous-phase chemistry for the fate of DMS and its oxidation products. Aqueous-phase processes significantly reduce the yield of sulfur dioxide and increase that of methyl sulfonic acid (MSA),which is needed to close the gap between modeled and measured MSA concentrations. Finally, the simulations imply that multiphase DMS oxidation produces equal amounts of MSA and sulfate, a result that has significant implications for nss-SO₄2− aerosol formation, cloud condensation nuclei concentration, and cloud albedo over oceans. Our findings show the deficiencies of parameterizations currently used in higher-scale models, which only treat gas-phase chemistry. Overall, this study shows that treatment of DMS chemistry in both gas and aqueous phases is essential to improve the accuracy of model predictions.
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The prevalence of obstructive coronary artery disease (CAD) in symptomatic patients referred for diagnostic testing has declined, warranting optimization of individualized diagnostic strategies.
This ...study sought to present a simple, clinically applicable tool enabling estimation of the likelihood of obstructive CAD by combining a pre-test probability (PTP) model (Diamond-Forrester approach using sex, age, and symptoms) with clinical risk factors and coronary artery calcium score (CACS).
The new tool was developed in a cohort of symptomatic patients (n = 41,177) referred for diagnostic testing. The risk factor–weighted clinical likelihood (RF-CL) was calculated through PTP and risk factors, while the CACS–weighted clinical likelihood (CACS-CL) added CACS. The 2 calculation models were validated in European and North American cohorts (n = 15,411) and compared with a recently updated PTP table.
The RF-CL and CACS-CL models predicted the prevalence of obstructive CAD more accurately in the validation cohorts than the PTP model, and markedly increased the area under the receiver-operating characteristic curves of obstructive CAD: for the PTP model, 72 (95% confidence intervals CI: 71 to 74); for the RF-CL model, 75 (95% CI: 74 to 76); and for the CACS-CL model, 85 (95% CI: 84 to 86). In total, 38% of the patients in the RF-CL group and 54% in the CACS-CL group were categorized as having a low clinical likelihood of CAD, as compared with 11% with the PTP model.
A simple risk factor and CACS-CL tool enables improved prediction and discrimination of patients with suspected obstructive CAD. The tool empowers reclassification of patients to low likelihood of CAD, who need no further testing.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Aliphatic amines are important constituents of the marine environment. However, their biogenic origins, formation processes and roles in atmospheric chemistry are still not well understood. Here we ...present measurements of monomethylamine (MMA), dimethylamine (DMA) and diethylamine (DEA) from two intensive sampling campaigns at the Cape Verde Atmospheric Observatory (CVAO), a remote marine station in the tropical Atlantic Ocean. The amines were measured in the sea surface microlayer (SML), in bulk seawater, in the gas and the submicron particulate aerosol phase. Additionally, a 24-month record of amine concentrations in aerosol particles, together with other particle constituents and biological and meteorological parameters, is presented. In the SML, mean amine concentrations were in the range 20–50 nmol L−1. The correlation of the amines to chlorophyll-a (R2 = 0.52) and the abundance of the diatom pigment fucoxanthin may indicate that amines were formed via algal production. Amine concentrations in the gas and particulate aerosol phases were dominated by DMA, with average concentrations of 4.5 ng m−3 and 5.6 ng m−3, respectively. Average MMA concentrations were 0.8 ng m−3 in the gas phase and 0.2 ng m−3 in the particle phase. DEA was present in the particle phase with an average concentration of 3.9 ng m−3, but was not detected in the gas phase. Sea to air fluxes for MMA and DMA were calculated from the seawater and gaseous amine concentrations; these varied from −8.7 E−14 to +4.0 E−13 mol m−2 s−1 and from −1.9 E−12 to +2.17 E−12 mol m−2 s−1, respectively. While the flux for MMA was mainly positive, suggesting an oceanic source for this analyte, the flux for DMA could be both positive and negative, indicating that 2-way transport may be occurring. Principal component analysis of the 24-month dataset of amines in aerosol particles revealed that the particulate amines were not directly linked to the identified sources. It seems that the transfer of amines was being determined by gas to particle conversion rather than via primary processes. The correlation of both seawater- and gas phase-amines with biological indicators suggests that they were partly linked and that the amine abundance in the atmosphere (gas phase) reflected biological processes in seawater. In contrast, particulate amine concentrations did not show such a direct response and might have other significant sources and environmental drivers.
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•Aliphatic amines are present in the tropical remote Atlantic Ocean and Atmosphere.•Amines in the seawater and gas phase are connected to biological activity.•Ocean can be a sink or a source of amines.•Sources of amines in the submicron particle phase are probably not of primary nature.
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Field measurements of the concentrations of dicarboxylic acids and related compounds (oxocarboxylic acids and α-dicarbonyls) in PM2.5 were conducted on a background island (Tuoji Island, China) over ...the Bohai Sea to better understand the effects of pollution downwind of the East Asian continental outflow. Air mass backward trajectory calculations demonstrated that the distributions of dicarboxylic acids and related compounds at Tuoji Island depended strongly on the East Asian continental outflow and correlated with the hours spent by an air parcel in the polluted boundary layer. Based on the data analysis, the sampling period was categorized into heavy aerosol pollution periods (HAPPs) and light aerosol pollution periods (LAPPs). The average concentration of dicarboxylic acids and related compounds during HAPPs (1280 ± 503 ng m−3) was approximately seven times higher than that during LAPPs (189 ± 90.8 ng m−3). The order of the major species of dicarboxylic acids and related compounds, ranked by concentrations, was oxalic acid (C2) > glyoxylic acid (ωC2) > succinic acid (C4) > terephthalic acid (tPh) during HAPPs, and C2 > malonic acid (C3) > ωC2 > C4 during LAPPs. Results of positive matrix factorization (PMF) showed that secondary sources were the dominant source of dicarboxylic acids and related compounds, with contributions of 38% and 57% during HAPPs and LAPPs, respectively. Primary sources of biomass burning and plastic waste burning were also significant during HAPPs (contributions: 26% and 20%, respectively) and LAPPs (contributions: 18% and 12%, respectively). The concentration ratios of C3 to C4 (C3/C4), C2 to C4 (C2/C4), fumaric acid to maleic acid (F/M), phthalic acid to azelaic acid (Ph/C9), adipic acid to azelaic acid (C6/C9), and the positive correlations of Ph or tPh with dicarboxylic acids, and levoglucosan with dicarboxylic acids and related compounds further support the PMF results.
•Molecular distributions of diacids and related compounds at a background island.•East Asian continental outflow was a key controlling factor.•Secondary formation was the dominant source.•Primary sources of biomass and plastic waste burning were also significant.
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In the marine environment, measurements of lipids as representative species
within different lipid classes have been performed to characterize their
oceanic sources and their transfer from the ocean ...into the atmosphere to
marine aerosol particles. The set of lipid classes includes hydrocarbons
(HC); fatty acid methyl esters (ME); free fatty acids (FFA); alcohols (ALC);
1,3-diacylglycerols (1,3 DG); 1,2-diacylglycerols (1,2 DG);
monoacylglycerols (MG); wax esters (WE); triacylglycerols (TG); and
phospholipids (PP) including phosphatidylglycerols (PG),
phosphatidylethanolamine (PE), phosphatidylcholines (PC), as well as
glycolipids (GL) which cover sulfoquinovosyldiacylglycerols (SQDG),
monogalactosyl-diacylglycerols (MGDG), digalactosyldiacylglycerols (DGDG)
and sterols (ST). These introduced lipid classes have been analyzed in the
dissolved and particulate fraction of seawater, differentiating between
underlying water (ULW) and the sea surface microlayer (SML) on the one hand.
On the other hand, they have been examined on ambient submicrometer aerosol
particle samples (PM1) which were collected at the Cape Verde
Atmospheric Observatory (CVAO) by applying concerted measurements. These
different lipids are found in all marine compartments but in different
compositions. Along the campaign, certain variabilities are observed for the
concentration of dissolved (∑DLULW: 39.8–128.5 µg L−1, ∑DLSML: 55.7–121.5 µg L−1) and
particulate (∑PLULW: 36.4–93.5 µg L−1, ∑PLSML: 61.0–118.1 µg L−1) lipids in the seawater of the
tropical North Atlantic Ocean. Only slight SML enrichments are observed for
the lipids with an enrichment factor EFSML of 1.1–1.4 (DL) and 1.0–1.7
(PL). On PM1 aerosol particles, a total lipid concentration between
75.2–219.5 ng m−3 (averaged: 119.9 ng m−3) is measured. As also
bacteria – besides phytoplankton sources – influence the lipid
concentrations in seawater and on the aerosol particles, the lipid abundance
cannot be exclusively explained by the phytoplankton tracer
(chlorophyll a). The concentration and enrichment of lipids in the SML are
not related to physicochemical properties which describe the surface
activity. On the aerosol particles, an EFaer (the enrichment factor on
the submicrometer aerosol particles compared to the SML) between 9×104–7×105 is observed. Regarding the individual lipid
groups on the aerosol particles, a statistically significant correlation
(R2=0.45, p=0.028) was found between EFaer and
lipophilicity (expressed by the KOW value), which was not present for
the SML. But simple physicochemical descriptors are overall not sufficient
to fully explain the transfer of lipids. As our findings show that
additional processes such as formation and degradation influence the
ocean–atmosphere transfer of both OM in general and of lipids in particular,
they have to be considered in OM transfer models. Moreover, our data suggest
that the extent of the enrichment of the lipid class constituents on the
aerosol particles might be related to the distribution of the lipid within
the bubble–air–water interface. The lipids TG and ALC which are preferably
arranged within the bubble interface are transferred to the aerosol
particles to the highest extent. Finally, the connection between ice
nucleation particles (INPs) in seawater, which are already active at higher
temperatures (−10 to −15 ∘C), and the lipid classes
PE and FFA suggests that lipids formed in the ocean have the potential to
contribute to (biogenic) INP activity when transferred into the atmosphere.
The oxidation of dimethyl sulfide (DMS) is key for the natural sulfate aerosol formation and its climate impact. Multiphase chemistry is an important oxidation pathway but neglected in current ...chemistry‐climate models. Here, the DMS chemistry in the aerosol‐chemistry‐climate model ECHAM‐HAMMOZ is extended to include multiphase methane sulfonic acid (MSA) formation in deliquesced aerosol particles, parameterized by reactive uptake. First simulations agree well with observed gas‐phase MSA concentrations. The implemented formation pathways are quantified to contribute up to 60% to the sulfate aerosol burden over the Southern Ocean and Arctic/Antarctic regions. While globally the impact on the aerosol radiative forcing almost levels off, a significantly more positive solar radiative forcing of up to +0.1 W m−2 is computed in the Arctic (>60°N). The findings imply the need of both further laboratory and model studies on the atmospheric multiphase oxidation of DMS.
Plain Language Summary
The emission of dimethyl sulfide (DMS) represents the largest natural reduced sulfur source into the atmosphere. There, DMS can be oxidized to sulfur dioxide, sulfuric acid, or methane sulfonic acid modifying the radiative properties of aerosol particles and clouds. DMS oxidation is represented in chemistry‐climate models by a limited number of very simplified reactions. Small changes in the parameter settings can have large effects, that's why these should be as accurate as possible. In this study, the DMS chemistry in ECHAM‐HAMMOZ was upgraded. Sensitivity simulations show variations in the natural aerosol radiative forcing due to the different schemes tested in this study. Further laboratory and process studies with models are therefore essential.
Key Points
Dimethyl sulfide (DMS) chemistry in chemistry‐climate simulations extended by multiphase methane sulfonic acid (MSA) formation provides more realistic MSA gas‐phase concentrations
Formation of MSA is very sensitive toward reactive uptake on deliquesced aerosol particles
In the Arctic, the extended DMS chemistry leads to a significantly less negative effective radiative forcing of sulfate aerosol
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Despite the high abundance of secondary aerosols in the
atmosphere, their formation mechanisms remain poorly understood. In this
study, the Master
Chemical Mechanism (MCM) and the Chemical ...Aqueous-Phase Radical Mechanism (CAPRAM) are used to investigate the multiphase formation
and processing of secondary aerosol constituents during the advection of air
masses towards the measurement site of Mt. Tai in northern China. Trajectories
with and without chemical–cloud interaction are modeled. Modeled radical and
non-radical concentrations demonstrate that the summit of Mt. Tai, with an
altitude of ∼1.5 km a.m.s.l., is characterized by a suburban
oxidants budget. The modeled maximum gas-phase concentrations of the OH radical
are 3.2×106 and 3.5×106 molec. cm−3 in simulations with and without cloud passages in the
air parcel, respectively. In contrast with previous studies at Mt. Tai, this
study has modeled chemical formation processes of secondary aerosol
constituents under day vs. night and cloud vs. non-cloud cases along the
trajectories towards Mt. Tai in detail. The model studies show that sulfate is
mainly produced in simulations where the air parcel is influenced by cloud
chemistry. Under the simulated conditions, the aqueous reaction of
HSO3- with H2O2 is the major contributor to sulfate
formation, contributing 67 % and 60 % in the simulations with cloud
and non-cloud passages, respectively. The modeled nitrate formation is
higher at nighttime than during daytime. The major pathway is aqueous-phase
N2O5 hydrolysis, with a contribution of 72 % when cloud
passages are considered and 70 % when they are not. Secondary organic aerosol
(SOA) compounds, e.g., glyoxylic, oxalic, pyruvic and malonic acid, are found
to be mostly produced from the aqueous oxidations of hydrated glyoxal,
hydrated glyoxylic acid, nitro-2-oxopropanoate and hydrated 3-oxopropanoic
acid, respectively. Sensitivity studies reveal that gaseous volatile organic compound (VOC) emissions
have a huge impact on the concentrations of modeled secondary aerosol
compounds. Increasing the VOC emissions by a factor of 2 leads to linearly
increased concentrations of the corresponding SOA compounds. Studies using
the relative incremental reactivity (RIR) method have identified isoprene,
1,3-butadiene and toluene as the key precursors for glyoxylic and oxalic
acid, but only isoprene is found to be a key precursor for pyruvic acid.
Additionally, the model investigations demonstrate that an increased aerosol
partitioning of glyoxal can play an important role in the aqueous-phase
formation of glyoxylic and oxalic acid. Overall, the present study is the
first that provides more detailed insights in the formation pathways of
secondary aerosol constituents at Mt. Tai and clearly emphasizes the
importance of aqueous-phase chemical processes on the production of
multifunctional carboxylic acids.
Air quality is a globally pressing issue as it poses a major threat for human health and ecosystems. Non-methane volatile organic compounds (NMVOCs) are highly reactive substances and known for their ...impact on O
3
, HO
x
(OH + HO
2
) and NO
x
(NO + NO
2
) concentrations. NMVOCs comprise a variety of anthropogenic and biogenic compounds with highly complex and entangled relations. Therefore, it is key to capture these interdependencies for any air quality assessment through modeling. Unfortunately, chemical mechanisms used for air quality modeling are often too simplified and partly outdated. Here, we present the development of the chemical mechanism URMELL (Urban and Remote cheMistry modELLing) comprising an extended chemical treatment of major anthropogenic and biogenic NMVOCs based on current knowledge. Box model simulations of standardized urban and remote conditions were performed with URMELL and other mechanisms, and the obtained concentration time profiles of key compounds were compared. High correlations (>0.9) with the benchmark mechanism MCMv3.3.1 are found for all urban conditions. For remote conditions, the simulations using URMELL have much higher oxidant concentrations, especially for OH reaching concentrations ∼10
6
molecules per cm
3
which is in the same range of measured ambient OH concentrations at remote isoprene-dominated sites. For further evaluation, URMELL was applied in the chemical transport model COSMO-MUSCAT and simulations for Germany in May 2014 were performed. Modeled O
3
, NO and NO
2
concentrations were compared with 57 measurement sites indicating improved ozone correlations for urban as well as remote isoprene-influenced sites than the currently applied mechanism.
URMELL, the new gas-phase chemical mechanism for Urban and Remote cheMistry modELLing with a comprehensive isoprene and aromatics chemistry scheme. URMELL includes various highly oxidized molecules which enable a direct and explicit SOA treatment.
The project MarParCloud (Marine biological production, organic
aerosol Particles and marine Clouds: a process
chain) aims to improve our understanding of the genesis, modification and
impact of ...marine organic matter (OM) from its biological production, to
its export to marine aerosol particles and, finally, to its ability to
act as ice-nucleating particles (INPs) and cloud condensation nuclei (CCN). A
field campaign at the Cape Verde Atmospheric Observatory (CVAO) in the
tropics in September–October 2017 formed the core of this project that was
jointly performed with the project MARSU (MARine atmospheric
Science Unravelled). A suite of chemical,
physical, biological and meteorological techniques was applied, and
comprehensive measurements of bulk water, the sea surface microlayer (SML),
cloud water and ambient aerosol particles collected at a ground-based and a
mountain station took place. Key variables comprised the chemical characterization of the atmospherically
relevant OM components in the ocean and the atmosphere as well as
measurements of INPs and CCN. Moreover, bacterial cell counts, mercury
species and trace gases were analyzed. To interpret the results, the
measurements were accompanied by various auxiliary parameters such as air
mass back-trajectory analysis, vertical atmospheric profile analysis, cloud
observations and pigment measurements in seawater. Additional modeling
studies supported the experimental analysis. During the campaign, the CVAO exhibited marine air masses with low and
partly moderate dust influences. The marine boundary layer was well mixed as
indicated by an almost uniform particle number size distribution within the
boundary layer. Lipid biomarkers were present in the aerosol particles in
typical concentrations of marine background conditions. Accumulation- and
coarse-mode particles served as CCN and were efficiently transferred to the
cloud water. The ascent of ocean-derived compounds, such as sea salt and
sugar-like compounds, to the cloud level, as derived from chemical analysis
and atmospheric transfer modeling results, denotes an influence of marine
emissions on cloud formation. Organic nitrogen compounds (free amino acids)
were enriched by several orders of magnitude in submicron aerosol particles
and in cloud water compared to seawater. However, INP measurements also indicated
a significant contribution of other non-marine sources to the local INP
concentration, as (biologically active) INPs were mainly present in
supermicron aerosol particles that are not suggested to undergo strong
enrichment during ocean–atmosphere transfer. In addition, the number of CCN
at the supersaturation of 0.30 % was about 2.5 times higher during dust
periods compared to marine periods. Lipids, sugar-like compounds, UV-absorbing (UV: ultraviolet) humic-like substances and low-molecular-weight neutral components
were important organic compounds in the seawater, and highly surface-active
lipids were enriched within the SML. The selective enrichment of specific
organic compounds in the SML needs to be studied in further detail and
implemented in an OM source function for emission modeling to better
understand transfer patterns, the mechanisms of marine OM transformation in the
atmosphere and the role of additional sources. In summary, when looking at particulate mass, we see oceanic compounds
transferred to the atmospheric aerosol and to the cloud level, while from a
perspective of particle number concentrations, sea spray aerosol (i.e.,
primary marine aerosol) contributions to both CCN and INPs are rather
limited.
Methanesulfonic acid (CH3SO3H, MSA) is one of the major organosulfur acids formed from the photochemical oxidation of dimethyl sulfide (DMS) produced by oceanic phytoplankton. MSA can react with ...metal halides (e.g., sodium chloride) in ambient aerosols to form methanesulfonate salts (e.g., sodium methanesulfonate, CH3SO3Na). While the formation processes of MSA and its salts are reasonably well understood, their subsequent chemical transformations in the atmosphere are not fully resolved. MSA and its salts accumulate near the aerosol surface due to their surface activities, which make them available to heterogeneous oxidation at the gas–aerosol interface by oxidants such as hydroxyl (OH) radicals. In this work, the compositional changes of aerosol comprised of MSA and its sodium salt (CH3SO3Na) are measured following heterogeneous OH oxidation. An aerosol flow tube reactor is coupled with a soft atmospheric pressure ionization source (Direct Analysis in Real Time, DART) and a high-resolution mass spectrometer at a relative humidity (RH) of 90%. DART-aerosol mass spectra reveal that MSA and CH3SO3Na can be detected as methanesulfonate ion (CH3SO3 –) with minimal fragmentation in the negative ionization mode. Kinetic measurements show that OH oxidation with MSA and CH3SO3Na has an effective OH uptake coefficient of 0.45 ± 0.14 and 0.20 ± 0.06, respectively, revealing that MSA reacts with OH radical faster than its sodium salt. One possibility for the difference in reactivity of these two compounds is that CH3SO3Na is more hygroscopic than MSA. The increase in the coverage of water molecules at the surface of CH3SO3Na might reduce the reactive collision probability between CH3SO3 – and OH radicals, resulting in a smaller reaction rate. MSA and CH3SO3Na dissociate to form CH3SO3 –, which tends to fragment into formaldehyde (HCHO) and a sulfite radical (SO3 •–) upon oxidation. Formaldehyde partitions back to the gas phase owing to its high volatility, and SO3 •– can initiate a series of chain reactions involving various inorganic sulfur radicals and ions in the aerosol phase. Overall, the fragmentation and SO3 •–-initiated chemistry are the major processes controlling the chemical evolution of MSA and its sodium salt aerosols during heterogeneous OH oxidation.
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