scholarly journals Modeling the partitioning of organic chemical species in cloud phases with CLEPS (1.1)

2017 ◽  
Author(s):  
Clémence Rose ◽  
Nadine Chaumerliac ◽  
Laurent Deguillaume ◽  
Hélène Perroux ◽  
Camille Mouchel-Vallon ◽  
...  
Keyword(s):  
Gas Phase ◽  
Carboxylic Acids ◽  
Aqueous Phase ◽  
Chemical Reactivity ◽  
Chemical Species ◽  
Coupled Model ◽  
Water Soluble ◽  
Organic Chemical ◽  
Particulate Phase ◽  
Particle Dissolution

Abstract. The new detailed aqueous phase mechanism Cloud Explicit Physico-chemical Scheme (CLEPS 1.0), which describes the oxidation of isoprene-derived water-soluble organic compounds, is coupled with a warm microphysical module simulating the activation of aerosol particles into cloud droplets. CLEPS 1.0 was then extended to CLEPS 1.1 to include the chemistry of the newly added di-carboxylic acids dissolved from the particulate phase. The resulting coupled model allows for predicting the aqueous phase concentrations of chemical compounds originating from particle dissolution, mass transfer from the gas phase and in-cloud aqueous chemical reactivity. The aim of the present study was more particularly to investigate the effect of particle dissolution on cloud chemistry. Several simulations were performed to assess the influence of various parameters on model predictions and to interpret long-term measurements conducted at the top of the puy de Dôme (PUY, France) in marine air masses. Specific attention was paid to carboxylic acids, whose predicted concentrations are on average in the lower range of the observations, with the exception of formic acid, which is rather overestimated in the model. The different sensitivity runs highlight the fact that formic and acetic acids mainly originate from the gas phase and have highly variable aqueous-phase reactivity depending on the cloud acidity, whereas C3–C4 carboxylic acids mainly originate from the particulate phase and are supersaturated in the cloud.

scholarly journals Modeling the partitioning of organic chemical species in cloud phases with CLEPS (1.1)

2018 ◽  
Vol 18 (3) ◽  
pp. 2225-2242 ◽  
Author(s):  
Clémence Rose ◽  
Nadine Chaumerliac ◽  
Laurent Deguillaume ◽  
Hélène Perroux ◽  
Camille Mouchel-Vallon ◽  
...  
Keyword(s):  
Gas Phase ◽  
Carboxylic Acids ◽  
Aqueous Phase ◽  
Chemical Reactivity ◽  
Chemical Species ◽  
Coupled Model ◽  
Water Soluble ◽  
Organic Chemical ◽  
Particulate Phase ◽  
Particle Scavenging

Abstract. The new detailed aqueous-phase mechanism Cloud Explicit Physico-chemical Scheme (CLEPS 1.0), which describes the oxidation of isoprene-derived water-soluble organic compounds, is coupled with a warm microphysical module simulating the activation of aerosol particles into cloud droplets. CLEPS 1.0 was then extended to CLEPS 1.1 to include the chemistry of the newly added dicarboxylic acids dissolved from the particulate phase. The resulting coupled model allows the prediction of the aqueous-phase concentrations of chemical compounds originating from particle scavenging, mass transfer from the gas-phase and in-cloud aqueous chemical reactivity. The aim of the present study was more particularly to investigate the effect of particle scavenging on cloud chemistry. Several simulations were performed to assess the influence of various parameters on model predictions and to interpret long-term measurements conducted at the top of Puy de Dôme (PUY, France) in marine air masses. Specific attention was paid to carboxylic acids, whose predicted concentrations are on average in the lower range of the observations, with the exception of formic acid, which is rather overestimated in the model. The different sensitivity runs highlight the fact that formic and acetic acids mainly originate from the gas phase and have highly variable aqueous-phase reactivity depending on the cloud acidity, whereas C3–C4 carboxylic acids mainly originate from the particulate phase and are supersaturated in the cloud.

scholarly journals Explicit modeling of volatile organic compounds partitioning in the atmospheric aqueous phase

2013 ◽  
Vol 13 (2) ◽  
pp. 1023-1037 ◽  
Author(s):  
C. Mouchel-Vallon ◽  
P. Bräuer ◽  
M. Camredon ◽  
R. Valorso ◽  
S. Madronich ◽  
...  
Keyword(s):  
Organic Matter ◽  
Dissolved Organic Matter ◽  
Water Content ◽  
Gas Phase ◽  
Aqueous Phase ◽  
Water Soluble ◽  
Chemical Mechanism ◽  
Organic Species ◽  
Cloud Water Content ◽  
Isoprene Oxidation

Abstract. The gas phase oxidation of organic species is a multigenerational process involving a large number of secondary compounds. Most secondary organic species are water-soluble multifunctional oxygenated molecules. The fully explicit chemical mechanism GECKO-A (Generator of Explicit Chemistry and Kinetics of Organics in the Atmosphere) is used to describe the oxidation of organics in the gas phase and their mass transfer to the aqueous phase. The oxidation of three hydrocarbons of atmospheric interest (isoprene, octane and α-pinene) is investigated for various NOx conditions. The simulated oxidative trajectories are examined in a new two dimensional space defined by the mean oxidation state and the solubility. The amount of dissolved organic matter was found to be very low (yield less than 2% on carbon atom basis) under a water content typical of deliquescent aerosols. For cloud water content, 50% (isoprene oxidation) to 70% (octane oxidation) of the carbon atoms are found in the aqueous phase after the removal of the parent hydrocarbons for low NOx conditions. For high NOx conditions, this ratio is only 5% in the isoprene oxidation case, but remains large for α-pinene and octane oxidation cases (40% and 60%, respectively). Although the model does not yet include chemical reactions in the aqueous phase, much of this dissolved organic matter should be processed in cloud drops and modify both oxidation rates and the speciation of organic species.

scholarly journals Identifying precursors and aqueous organic aerosol formation pathways during the SOAS campaign

2016 ◽  
Vol 16 (22) ◽  
pp. 14409-14420 ◽  
Author(s):  
Neha Sareen ◽  
Annmarie G. Carlton ◽  
Jason D. Surratt ◽  
Avram Gold ◽  
Ben Lee ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Gas Phase ◽  
Aqueous Phase ◽  
Organic Aerosol ◽  
Water Soluble ◽  
Negative Ion ◽  
Anthropogenic Sources ◽  
Ionization Mass ◽  
Aqueous Mixtures ◽  
Aerosol Formation

Abstract. Aqueous multiphase chemistry in the atmosphere can lead to rapid transformation of organic compounds, forming highly oxidized, low-volatility organic aerosol and, in some cases, light-absorbing (brown) carbon. Because liquid water is globally abundant, this chemistry could substantially impact climate, air quality, and health. Gas-phase precursors released from biogenic and anthropogenic sources are oxidized and fragmented, forming water-soluble gases that can undergo reactions in the aqueous phase (in clouds, fogs, and wet aerosols), leading to the formation of secondary organic aerosol (SOAAQ). Recent studies have highlighted the role of certain precursors like glyoxal, methylglyoxal, glycolaldehyde, acetic acid, acetone, and epoxides in the formation of SOAAQ. The goal of this work is to identify additional precursors and products that may be atmospherically important. In this study, ambient mixtures of water-soluble gases were scrubbed from the atmosphere into water at Brent, Alabama, during the 2013 Southern Oxidant and Aerosol Study (SOAS). Hydroxyl (OH⚫) radical oxidation experiments were conducted with the aqueous mixtures collected from SOAS to better understand the formation of SOA through gas-phase followed by aqueous-phase chemistry. Total aqueous-phase organic carbon concentrations for these mixtures ranged from 92 to 179 µM-C, relevant for cloud and fog waters. Aqueous OH-reactive compounds were primarily observed as odd ions in the positive ion mode by electrospray ionization mass spectrometry (ESI-MS). Ultra high-resolution Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) spectra and tandem MS (MS–MS) fragmentation of these ions were consistent with the presence of carbonyls and tetrols. Products were observed in the negative ion mode and included pyruvate and oxalate, which were confirmed by ion chromatography. Pyruvate and oxalate have been found in the particle phase in many locations (as salts and complexes). Thus, formation of pyruvate/oxalate suggests the potential for aqueous processing of these ambient mixtures to form SOAAQ.

scholarly journals Dissolved organic carbon (DOC) and select aldehydes in cloud and fog water: the role of the aqueous phase in impacting trace gas budgets

2013 ◽  
Vol 13 (10) ◽  
pp. 5117-5135 ◽  
Author(s):  
B. Ervens ◽  
Y. Wang ◽  
J. Eagar ◽  
W. R. Leaitch ◽  
A. M. Macdonald ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Gas Phase ◽  
Aqueous Phase ◽  
Water Soluble ◽  
Box Model ◽  
High Solubility ◽  
Fog Water ◽  
Air Masses ◽  
Order Of Magnitude

Abstract. Cloud and fog droplets efficiently scavenge and process water-soluble compounds and, thus, modify the chemical composition of the gas and particle phases. The concentrations of dissolved organic carbon (DOC) in the aqueous phase reach concentrations on the order of ~ 10 mgC L−1 which is typically on the same order of magnitude as the sum of inorganic anions. Aldehydes and carboxylic acids typically comprise a large fraction of DOC because of their high solubility. The dissolution of species in the aqueous phase can lead to (i) the removal of species from the gas phase preventing their processing by gas phase reactions (e.g., photolysis of aldehydes) and (ii) the formation of unique products that do not have any efficient gas phase sources (e.g., dicarboxylic acids). We present measurements of DOC and select aldehydes in fog water at high elevation and intercepted clouds at a biogenically-impacted location (Whistler, Canada) and in fog water in a more polluted area (Davis, CA). Concentrations of formaldehyde, glyoxal and methylglyoxal were in the micromolar range and comprised ≤ 2% each individually of the DOC. Comparison of the DOC and aldehyde concentrations to those at other locations shows good agreement and reveals highest levels for both in anthropogenically impacted regions. Based on this overview, we conclude that the fraction of organic carbon (dissolved and insoluble inclusions) in the aqueous phase of clouds or fogs, respectively, comprises 2–~ 40% of total organic carbon. Higher values are observed to be associated with aged air masses where organics are expected to be more highly oxidised and, thus, more soluble. Accordingly, the aqueous/gas partitioning ratio expressed here as an effective Henry's law constant for DOC (KH*DOC) increases by an order of magnitude from 7 × 103 M atm−1 to 7 × 104 M atm−1 during the ageing of air masses. The measurements are accompanied by photochemical box model simulations. These simulations are used to contrast two scenarios, i.e., an anthropogenically vs. a more biogenically impacted one as being representative for Davis and Whistler, respectively. Since the simplicity of the box model prevents a fully quantitative prediction of the observed aldehyde concentrations, we rather use the model results to compare trends in aldehyde partitioning and ratios. They suggest that the scavenging of aldehydes by the aqueous phase can reduce HO2 gas phase levels significantly by two orders of magnitude due to a weaker net source of HO2 production from aldehyde photolysis in the gas phase. Despite the high solubility of dicarbonyl compounds (glyoxal, methylglyoxal), their impact on the HO2 budget by scavenging is < 10% of that of formaldehyde. The overview of DOC and aldehyde measurements presented here reveals that clouds and fogs can be efficient sinks for organics, with increasing importance in aged air masses. Even though aldehydes, specifically formaldehyde, only comprise ~ 1% of DOC, their scavenging and processing in the aqueous phase might translate into significant effects in the oxidation capacity of the atmosphere.

scholarly journals Aqueous-phase mechanism for secondary organic aerosol formation from isoprene: application to the southeast United States and co-benefit of SO<sub>2</sub> emission controls

2016 ◽  
Vol 16 (3) ◽  
pp. 1603-1618 ◽  
Author(s):  
E. A. Marais ◽  
D. J. Jacob ◽  
J. L. Jimenez ◽  
P. Campuzano-Jost ◽  
D. A. Day ◽  
...  
Keyword(s):  
Gas Phase ◽  
Aqueous Phase ◽  
Secondary Organic Aerosol ◽  
Organic Aerosol ◽  
Water Soluble ◽  
So2 Emissions ◽  
Aerosol Acidity ◽  
Emission Controls ◽  
Isoprene Oxidation ◽  
Southeast Us

Abstract. Isoprene emitted by vegetation is an important precursor of secondary organic aerosol (SOA), but the mechanism and yields are uncertain. Aerosol is prevailingly aqueous under the humid conditions typical of isoprene-emitting regions. Here we develop an aqueous-phase mechanism for isoprene SOA formation coupled to a detailed gas-phase isoprene oxidation scheme. The mechanism is based on aerosol reactive uptake coefficients (γ) for water-soluble isoprene oxidation products, including sensitivity to aerosol acidity and nucleophile concentrations. We apply this mechanism to simulation of aircraft (SEAC4RS) and ground-based (SOAS) observations over the southeast US in summer 2013 using the GEOS-Chem chemical transport model. Emissions of nitrogen oxides (NOx  ≡  NO + NO2) over the southeast US are such that the peroxy radicals produced from isoprene oxidation (ISOPO2) react significantly with both NO (high-NOx pathway) and HO2 (low-NOx pathway), leading to different suites of isoprene SOA precursors. We find a mean SOA mass yield of 3.3 % from isoprene oxidation, consistent with the observed relationship of total fine organic aerosol (OA) and formaldehyde (a product of isoprene oxidation). Isoprene SOA production is mainly contributed by two immediate gas-phase precursors, isoprene epoxydiols (IEPOX, 58 % of isoprene SOA) from the low-NOx pathway and glyoxal (28 %) from both low- and high-NOx pathways. This speciation is consistent with observations of IEPOX SOA from SOAS and SEAC4RS. Observations show a strong relationship between IEPOX SOA and sulfate aerosol that we explain as due to the effect of sulfate on aerosol acidity and volume. Isoprene SOA concentrations increase as NOx emissions decrease (favoring the low-NOx pathway for isoprene oxidation), but decrease more strongly as SO2 emissions decrease (due to the effect of sulfate on aerosol acidity and volume). The US Environmental Protection Agency (EPA) projects 2013–2025 decreases in anthropogenic emissions of 34 % for NOx (leading to a 7 % increase in isoprene SOA) and 48 % for SO2 (35 % decrease in isoprene SOA). Reducing SO2 emissions decreases sulfate and isoprene SOA by a similar magnitude, representing a factor of 2 co-benefit for PM2.5 from SO2 emission controls.

scholarly journals Dissolved organic carbon (DOC) and select aldehydes in cloud and fog water: the role of the aqueous phase in impacting trace gas budgets

2012 ◽  
Vol 12 (12) ◽  
pp. 33083-33125 ◽  
Author(s):  
B. Ervens ◽  
Y. Wang ◽  
J. Eagar ◽  
W. R. Leaitch ◽  
A. M. Macdonald ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Dissolved Organic Carbon ◽  
Gas Phase ◽  
Aqueous Phase ◽  
Large Fraction ◽  
Water Soluble ◽  
High Solubility ◽  
Fog Water ◽  
Air Masses ◽  
Order Of Magnitude

Abstract. Cloud and fog droplets efficiently scavenge and process water-soluble compounds and thus modify the chemical composition of the gas and particle phases. The concentrations of dissolved organic carbon (DOC) in the aqueous phase reach concentrations on the order of ~10 mg C L−1 which is typically on the same order of magnitude as the sum of inorganic anions. Aldehydes and carboxylic acids typically comprise a large fraction of DOC because of their high solubility. The dissolution of species in the aqueous phase can lead to (i) the removal of species from the gas phase preventing their processing by gas phase reactions (e.g. photolysis of aldehydes) and (ii) the formation of unique products that do not have any efficient gas phase sources (e.g. dicarboxylic acids). We present measurements of DOC and select aldehydes in fog water at high elevation and intercepted clouds in a biogenically-impacted location (Whistler, Canada) and in fog water in a more polluted area (Davis, CA). Concentrations of formaldehyde, glyoxal and methylglyoxal were in the micromolar range and comprised ≤2% each individually of the DOC. Comparison of the DOC and aldehyde concentrations to those at other locations shows good agreement and reveals highest levels for both in anthropogenically impacted regions. Based on this overview, we conclude that the fraction of organic carbon (dissolved and insoluble inclusions) in the aqueous phase comprises 1–~40% of total organic carbon. Higher values are observed to be associated with aged air masses where organics are expected to be more highly oxidized and thus more soluble. Accordingly, the aqueous/gas partitioning ratio expressed here as an effective Henry's law constant for DOC (KH*DOC) increases by an order of magnitude from 7×103 M atm−1 to 7×104 M atm−1 during the ageing of air masses. The measurements are accompanied by photochemical box model simulations. They suggest that the scavenging of aldehydes by the aqueous phase can reduce HO2 gas phase levels by two orders of magnitude due to a weaker net source of HO2 production from aldehyde photolysis in the gas phase. Despite the high solubility of dialdehydes (glyoxal, methylglyoxal), their impact on the HO2 budget by scavenging is <10% of that of formaldehyde. The overview of DOC and aldehyde measurements presented here reveals that clouds and fogs can be efficient sinks for organics, with increasing importance in aged air masses. Even though aldehydes, specifically formaldehyde, only comprise ~1% of DOC, their scavenging and processing in the aqueous phase might translate into significant effects on the oxidation capacity of the atmosphere.

scholarly journals Identifying precursors and aqueous organic aerosol formation pathways during the SOAS campaign

2016 ◽  
Author(s):  
Neha Sareen ◽  
Annmarie G. Carlton ◽  
Jason D. Surratt ◽  
Avram Gold ◽  
Ben Lee ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Gas Phase ◽  
Aqueous Phase ◽  
Organic Aerosol ◽  
Water Soluble ◽  
Negative Ion ◽  
Anthropogenic Sources ◽  
Ionization Mass ◽  
Aqueous Mixtures ◽  
Aerosol Formation

Abstract. Aqueous multiphase chemistry in the atmosphere can lead to rapid transformation of organic compounds, forming highly oxidized low-volatility organic aerosol and, in some cases, light-absorbing (brown) carbon. Because liquid water is globally abundant, this chemistry could substantially impact climate, air quality, and health. Gas-phase precursors released from biogenic and anthropogenic sources are oxidized and fragmented, forming water-soluble gases that can undergo reactions in the aqueous phase (in clouds, fogs, and wet aerosols) leading to the formation of secondary organic aerosol (SOAAQ). Recent studies have highlighted the role of certain precursors like glyoxal, methylglyoxal, glycolaldehyde, acetic acid, acetone, and epoxides in the formation of SOAAQ. The goal of this work is to identify additional precursors and products that may be atmospherically important. In this study, ambient mixtures of water-soluble gases were scrubbed from the atmosphere into water at Brent, Alabama during the 2013 Southern Oxidant and Aerosol Study (SOAS). Hydroxyl (OH•) radical oxidation experiments were conducted with the aqueous mixtures collected from SOAS to better understand the formation of SOA through gas-phase followed by aqueous-phase chemistry. Total aqueous-phase organic carbon concentrations for these mixtures ranged from 92–179 µM-C, relevant for cloud and fog waters. Aqueous OH-reactive compounds were primarily observed as odd ions in the positive ion mode by electrospray ionization mass spectrometry (ESI-MS), indicative of alcohols, carbonyl compounds, and/or epoxides. Ultra high-resolution Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) spectra and tandem MS (MS/MS) fragmentation of these ions were consistent with the presence of carbonyls and tetrols. Products were observed in the negative ion mode and included pyruvate and oxalate, which were confirmed by ion chromatography. Pyruvate and oxalate have been found in the particle phase in many locations (e.g., as salts and complexes). Thus, formation of pyruvate/oxalate suggests the potential for aqueous processing of these ambient mixtures to form SOAAQ.

scholarly journals Chemical characteristics of cloud water and the impacts on aerosol properties at a subtropical mountain site in Hong Kong

2019 ◽  
Author(s):  
Tao Li ◽  
Zhe Wang ◽  
Yaru Wang ◽  
Chen Wu ◽  
Yiheng Liang ◽  
...  
Keyword(s):  
Hong Kong ◽  
Chemical Composition ◽  
Gas Phase ◽  
Carboxylic Acids ◽  
Carbonyl Compounds ◽  
Cloud Water ◽  
Water Soluble ◽  
Soluble Ions ◽  
Aerosol Cloud Interactions ◽  
Aerosol Properties

Abstract. To investigate the cloud water chemistry and the effects of cloud processes on aerosol properties, comprehensive field observations of cloud water, aerosols, and gas-phase species were conducted at a mountaintop site in Hong Kong in October and November 2016. The chemical composition of cloud water including water-soluble ions, dissolved organic matter (DOM), carbonyl compounds, carboxylic acids, and trace metals was quantified. The measured cloud water was very acidic with a mean pH of 3.63, as the ammonium (174 μeq L−1) was insufficient for neutralizing the dominant sulfate (230 μeq L−1) and nitrate (160 μeq L−1). Substantial DOM was found in cloud water, with carbonyl compounds and carboxylic acids accounting for 18.2 % and 5.6 %, respectively. Different from previous observations, concentrations of methylglyoxal (19.1 μM) and glyoxal (6.72 μM) were higher than that of formaldehyde (1.59 μM). The partitioning of carbonyls between cloud water and the gas phase was also investigated. The measured aqueous fractions of dicarbonyls were comparable to the theoretical estimations, while significant aqueous-phase supersaturation was found for less soluble monocarbonyls, suggesting complicated effects of both physical and chemical processes. In-cloud oxidation played an important role in increasing DOM and sulfate in the cloud water. Abundant glyoxal is suggested to be the most likely precursor of cloud water organics. The aqueous formation of organics was enhanced by photochemistry and under less-acidic conditions. Moreover, as a result of the cloud processes, DOM mass fractions were found to be significantly elevated in in-cloud aerosols, which was likely to contribute to the increase in droplet-mode mass fraction of cloud processed aerosols. This study demonstrates the significant role of clouds in altering the chemical composition and physical properties of aerosols via scavenging and aqueous processes, and provides valuable information about aerosol–cloud interactions in subtropical and coastal regions.

scholarly journals Formation mechanism and source apportionment of water-soluble organic carbon in PM<sub>1</sub>, PM<sub>2.5</sub> and PM<sub>10</sub> in Beijing during haze episodes

2018 ◽  
Author(s):  
Qing Yu ◽  
Jing Chen ◽  
Weihua Qin ◽  
Yuepeng Zhang ◽  
Siming Cheng ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Gas Phase ◽  
Aqueous Phase ◽  
Water Soluble ◽  
Distribution Characteristics ◽  
Secondary Sources ◽  
Phase Oxidation ◽  
Water Soluble Organic Carbon ◽  
Soluble Organic Carbon ◽  
Haze Episode

Abstract. Water soluble organic carbon (WSOC) in atmospheric aerosols may pose significant impacts on haze formation, climate change, and human health. This study investigated the distribution characteristics and sources of WSOC in Beijing based on the diurnal PM1, PM2.5 and PM10 samples collected during haze episodes in winter and early spring of 2017. The haze episode in winter showed elevated level of WSOC, around three times of that in spring. WSOC was enriched in PM2.5 in winter while the proportions in both finer (0–1 μm) and coarse particles (2.5–10 μm) increased in spring. Several organic tracers were carefully selected and measured to demonstrate the sources and formation mechanism of WSOC. Most of the identified organic tracers showed similar seasonal variation, diurnal change and size distributions with WSOC, while the biogenic secondary organic aerosol (SOA) tracer cis-pinonic acid was an obvious exception. Based on the distribution characteristics of the secondary organic tracers and their correlation patterns with key influencing factors, the importance of the gas-phase versus aqueous-phase oxidation processes on SOA formation was explored. The gas-phase photochemical oxidation was weakened during haze episodes, whereas the aqueous-phase oxidation became the major pathway of SOA formation, especially in winter, at night and for the coarser particles. Secondary sources accounted for more than 50 % of WSOC in both winter and spring. Biomass burning was not the dominant source of WSOC in Beijing during haze episodes. Primary sources showed greater influence on finer particles while secondary sources became more important for coarser particles during haze episode in winter. SOC estimated by the OC-EC method, WSOC-levoglucosan method, and PMF-based methods were comparable, and the potential errors for different SOC estimation methods were discussed.

scholarly journals Chemical characteristics of cloud water and the impacts on aerosol properties at a subtropical mountain site in Hong Kong SAR

2020 ◽  
Vol 20 (1) ◽  
pp. 391-407 ◽  
Author(s):  
Tao Li ◽  
Zhe Wang ◽  
Yaru Wang ◽  
Chen Wu ◽  
Yiheng Liang ◽  
...  
Keyword(s):  
Hong Kong ◽  
Gas Phase ◽  
Carboxylic Acids ◽  
Carbonyl Compounds ◽  
Cloud Water ◽  
Water Soluble ◽  
Chemical Compositions ◽  
Soluble Ions ◽  
Hong Kong Sar ◽  
Aerosol Properties

Abstract. To investigate the cloud water chemistry and the effects of cloud processing on aerosol properties, comprehensive field observations of cloud water, aerosols, and gas-phase species were conducted at a mountaintop site in Hong Kong SAR in October and November 2016. The chemical composition of cloud water including water-soluble ions, dissolved organic matter (DOM), carbonyl compounds (refer to aldehydes and acetone), carboxylic acids, and trace metals was quantified. The measured cloud water was very acidic with a mean pH of 3.63, as the ammonium (174 µeq L−1) was insufficient for neutralizing the dominant sulfate (231 µeq L−1) and nitrate (160 µeq L−1). Substantial DOM (9.3 mgC L−1) was found in cloud water, with carbonyl compounds and carboxylic acids accounting for 18 % and 6 % in carbon molar concentrations, respectively. Different from previous observations, concentrations of methylglyoxal (19.1 µM; µM is equal to µmol L−1) and glyoxal (6.72 µM) were higher than that of formaldehyde (1.59 µM). The partitioning of carbonyls between cloud water and the gas phase was also investigated. The measured aqueous fractions of dicarbonyls were comparable to the theoretical estimations, while significant aqueous-phase supersaturation was found for less soluble monocarbonyls. Both organics and sulfate were significantly produced in cloud water, and the aqueous formation of organics was more enhanced by photochemistry and under less acidic conditions. Moreover, elevated sulfate and organics were measured in the cloud-processed aerosols, and they were expected to contribute largely to the increase in droplet-mode aerosol mass fraction. This study demonstrates the significant role of clouds in altering the chemical compositions and physical properties of aerosols via scavenging and aqueous chemical processing, providing valuable information about gas–cloud–aerosol interactions in subtropical and coastal regions.

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