Ship impacts on the marine atmosphere: insights into the contribution of shipping emissions to the properties of marine aerosol and clouds

Abstract. We report properties of marine aerosol and clouds measured in the shipping lanes between Monterey Bay and San Francisco off the coast of Central California. Using a suite of aerosol instrumentation onboard the CIRPAS Twin Otter aircraft, these measurements represent a unique set of data contrasting the properties of clean and ship-impacted marine air masses in dry aerosol and cloud droplet residuals. Below-cloud aerosol exhibited average mass and number concentrations of 2 μg m−3 and 510 cm−3, respectively, which are consistent with previous studies performed off the coast of California. Enhancements in vanadium and cloud droplet number concentrations are observed concurrently with a decrease in cloud water pH, suggesting that periods of high aerosol loading are primarily linked to increased ship influence. Mass spectra from a compact time-of-flight Aerodyne aerosol mass spectrometer reveal an enhancement in the fraction of organic at m/z 42 (f42) and 99 (f99) in ship-impacted clouds. These ions are well correlated to each other (R2>0.64) both in and out of cloud and constitute 14% (f44) and 3% (f99) of organic mass during periods of enhanced sulfate. High-resolution mass spectral analysis of these masses from ship measurements suggests that the ions responsible for this variation were oxidized, possibly due to cloud processing. We propose that the organic fractions of these ions be used as a metric for determining the extent to which cloud-processed ship emissions impact the marine atmosphere where (f42 > 0.15; f99 > 0.04) would imply heavy influence from shipping emissions, (0.05 < f42 < 0.15; 0.01 < f99 < 0.04) would imply moderate, but persistent, influences from ships, and (f42 < 0.05; f99 < 0.01) would imply clean, non-ship-influenced air.

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Ship impacts on the marine atmosphere: insights into the contribution of shipping emissions to the properties of marine aerosol and clouds

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-12-14393-2012 ◽

2012 ◽

Vol 12 (6) ◽

pp. 14393-14445 ◽

Cited By ~ 1

Author(s):

M. M. Coggon ◽

A. Sorooshian ◽

Z. Wang ◽

A. R. Metcalf ◽

A. A. Frossard ◽

...

Keyword(s):

San Francisco ◽

Cloud Droplet ◽

Marine Atmosphere ◽

Marine Aerosol ◽

Average Mass ◽

Mass Spectral ◽

Cloud Processing ◽

Aerosol Mass ◽

Water Ph ◽

Aerosol Instrumentation

Abstract. We report properties of marine aerosol and clouds measured in the shipping lanes between Monterey Bay and San Francisco off the coast of Central California. Using a suite of aerosol instrumentation onboard the CIRPAS Twin Otter aircraft, these measurements represent a unique set of data contrasting the properties of clean and ship-impacted marine air masses in dry aerosol and cloud droplet residuals. Average mass and number concentrations of below-cloud aerosol of 2 μg m−3 and 510 cm−3 are consistent with previous studies performed off the coast of California. Enhancement of vanadium and cloud droplet number concentration observed concurrently with a decrease in cloud water pH suggests that periods of high aerosol loading are primarily linked to increased ship influence. Mass spectra from a compact time-of-flight Aerodyne aerosol mass spectrometer reveal an enhancement in the fraction of organic at m/z 42 (f42) and 99 (f99) in ship-impacted clouds. These ions are well correlated to each other (R2 > 0.64) both in and out of cloud and dominate organic mass during periods of enhanced sulfate. High-resolution mass spectral analysis of these masses from ship measurements suggests that the ions responsible for this variation were oxidized, possibly due to cloud processing. We propose that the organic fractions of these ions be used as a metric for determining the extent to which ships impact the marine atmosphere where (f42 > 0.15; f99 > 0.04) would imply heavy influence from shipping emissions, (0.05 < f42 < 0.15; 0.01 < f99 < 0.04) would imply moderate, but persistent, influences from ships, and (f42 < 0.05; f99 < 0.01) would imply clean, non-ship-influenced air.

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The analysis of size-segregated cloud condensation nuclei counter (CCNC) data and its implications for cloud droplet activation

Atmospheric Chemistry and Physics ◽

10.5194/acp-13-10285-2013 ◽

2013 ◽

Vol 13 (20) ◽

pp. 10285-10301 ◽

Cited By ~ 45

Author(s):

M. Paramonov ◽

P. P. Aalto ◽

A. Asmi ◽

N. Prisle ◽

V.-M. Kerminen ◽

...

Keyword(s):

Cloud Condensation Nuclei ◽

Critical Diameter ◽

Cloud Droplet ◽

Condensation Nuclei ◽

Ambient Aerosol ◽

Cloud Processing ◽

Aerosol Mass ◽

Diurnal Patterns ◽

Hygroscopic Properties ◽

Boreal Environment

Abstract. Ambient aerosol, CCN (cloud condensation nuclei) and hygroscopic properties were measured with a size-segregated CCNC (cloud condensation nuclei counter) in a boreal environment of southern Finland at the SMEAR (Station for Measuring Ecosystem-Atmosphere Relations) II station. The instrumental setup operated at five levels of supersaturation S covering a range from 0.1–1% and measured particles with a size range of 20–300 nm; a total of 29 non-consecutive months of data are presented. The median critical diameter Dc ranged from 150 nm at S of 0.1% to 46 nm at S of 1.0%. The median aerosol hygroscopicity parameter κ ranged from 0.41 at S of 0.1% to 0.14 at S of 1.0%, indicating that ambient aerosol in Hyytiälä is less hygroscopic than the global continental or European continental averages. It is, however, more hygroscopic than the ambient aerosol in an Amazon rainforest, a European high Alpine site or a forested mountainous site. A fairly low hygroscopicity in Hyytiälä is likely a result of a large organic fraction present in the aerosol mass comparative to other locations within Europe. A considerable difference in particle hygroscopicity was found between particles smaller and larger than ~100 nm in diameter, possibly pointing out to the effect of cloud processing increasing κ of particles > 100 nm in diameter. The hygroscopicity of the smaller, ~50 nm particles did not change seasonally, whereas particles with a diameter of ~150 nm showed a decreased hygroscopicity in the summer, likely resulting from the increased VOC emissions of the surrounding boreal forest and secondary organic aerosol (SOA) formation. For the most part, no diurnal patterns of aerosol hygroscopic properties were found. Exceptions to this were the weak diurnal patterns of small, ~50 nm particles in the spring and summer, when a peak in hygroscopicity around noon was observed. No difference in CCN activation and hygroscopic properties was found on days with or without atmospheric new particle formation. During all seasons, except summer, a CCN-inactive fraction was found to be present, rendering the aerosol of 75–300 nm in diameter as internally mixed in the summer and not internally mixed for the rest of the year.

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Influences of in-cloud aerosol scavenging parameterizations on aerosol concentrations and wet deposition in ECHAM5-HAM

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-9-22041-2009 ◽

2009 ◽

Vol 9 (5) ◽

pp. 22041-22101 ◽

Cited By ~ 3

Author(s):

B. Croft ◽

U. Lohmann ◽

R. V. Martin ◽

P. Stier ◽

S. Wurzler ◽

...

Keyword(s):

Wet Deposition ◽

Cloud Droplet ◽

Ice Crystal ◽

Cloud Processing ◽

Aerosol Cloud ◽

Aerosol Mass ◽

Cloud Scavenging ◽

Nucleation Scavenging ◽

Scavenging Ratios ◽

Global Mean

Abstract. A diagnostic nucleation scavenging scheme, which determines stratiform cloud scavenging ratios for both aerosol mass and number distributions, based on cloud droplet, and ice crystal number concentrations, is introduced into the ECHAM5-HAM global climate model. This is coupled with a size-dependent in-cloud impaction scavenging parameterization for both cloud droplet-aerosol, and ice crystal-aerosol collisions. Sensitivity studies are presented, which compare aerosol concentrations, and deposition between a variety of in-cloud scavenging approaches, including prescribed fractions, several diagnostic schemes, and a prognostic aerosol cloud processing treatment that passes aerosol in-droplet and in-ice crystal concentrations between model time steps. For one sensitivity study, assuming 100% of the in-cloud aerosol is scavenged into the cloud droplets and ice crystals, the annual global mean accumulation mode number burden is decreased by 65%, relative to a simulation with prognostic aerosol cloud processing. Diagnosing separate nucleation scavenging ratios for aerosol number and mass distributions, as opposed to equating the aerosol mass scavenging to the number scavenging ratios, reduces the annual global mean sulfate burden by near to 10%. The annual global mean sea salt burden is 30% lower for the diagnostic approach, which does not carry aerosol in-droplet and in-crystal concentrations between model time-steps as compared to the prognostic scheme. Implementation of in-cloud impaction scavenging reduced the annual, global mean black carbon burden by 30% for the prognostic aerosol cloud processing scheme. Better agreement with observations of black carbon profiles from aircraft (changes near to one order of magnitude for mixed phase clouds), 210Pb surface layer concentrations and wet deposition, and the geographic distribution of aerosol optical depth are found for the new diagnostic scavenging as compared to prescribed ratio scavenging scheme of the standard ECHAM5-HAM.

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Evaluation of the global oceanic isoprene source and its impacts on marine organic carbon aerosol

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-8-16445-2008 ◽

2008 ◽

Vol 8 (4) ◽

pp. 16445-16471 ◽

Cited By ~ 4

Author(s):

S. R. Arnold ◽

D. V. Spracklen ◽

J. Williams ◽

N. Yassaa ◽

J. Sciare ◽

...

Keyword(s):

Organic Carbon ◽

Scale Up ◽

Organic Aerosol ◽

Marine Atmosphere ◽

Marine Aerosol ◽

Aerosol Mass ◽

Phytoplankton Communities ◽

The Mean ◽

Global Oceans ◽

Northern And Southern Hemispheres

Abstract. We have combined the first satellite maps of the global distribution of phytoplankton functional type and new measurements of phytoplankton-specific isoprene productivities, with available remote marine isoprene observations and a global model, to evaluate our understanding of the marine isoprene source and its impacts on organic aerosol abundances. Using satellite products to scale up data on phytoplankton-specific isoprene productivity to the global oceans, we infer a mean "bottom-up" oceanic isoprene emission of 0.31±0.08 (1 σ) Tg/yr. By minimising the mean bias between the model and isoprene observations in the marine atmosphere remote from the continents, we produce a "top-down" oceanic isoprene source estimate of 1.9 Tg/yr. We suggest our reliance on limited atmospheric isoprene data, and limited knowledge of isoprene productivity across the broad range of phytoplankton communities in the oceans as contributors to this difference between the two estimates. Inclusion of secondary organic aerosol (SOA) production from oceanic isoprene in the model with a 2% yield produces small contributions (0.01–1.6%) to observed organic carbon (OC) aerosol mass at three remote marine sites in the Northern and Southern Hemispheres. In addition, we find the seasonal cycle of the isoprene SOA source is out of phase with the observed cycle in OC in the remote Southern Ocean. Based on these findings we suggest an insignificant role for isoprene in modulating remote marine aerosol abundances, giving further support to a recently postulated primary OC source in the remote marine atmosphere.

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Large contribution to secondary organic aerosol from isoprene cloud chemistry

Science Advances ◽

10.1126/sciadv.abe2952 ◽

2021 ◽

Vol 7 (13) ◽

pp. eabe2952

Author(s):

Houssni Lamkaddam ◽

Josef Dommen ◽

Ananth Ranjithkumar ◽

Hamish Gordon ◽

Günther Wehrle ◽

...

Keyword(s):

Radiative Forcing ◽

Flow Reactor ◽

Secondary Organic Aerosol ◽

Cloud Droplet ◽

Organic Aerosol ◽

Global Scale ◽

Oxidation Products ◽

Oh Radicals ◽

Large Contribution ◽

Cloud Processing

Aerosols still present the largest uncertainty in estimating anthropogenic radiative forcing. Cloud processing is potentially important for secondary organic aerosol (SOA) formation, a major aerosol component: however, laboratory experiments fail to mimic this process under atmospherically relevant conditions. We developed a wetted-wall flow reactor to simulate aqueous-phase processing of isoprene oxidation products (iOP) in cloud droplets. We find that 50 to 70% (in moles) of iOP partition into the aqueous cloud phase, where they rapidly react with OH radicals, producing SOA with a molar yield of 0.45 after cloud droplet evaporation. Integrating our experimental results into a global model, we show that clouds effectively boost the amount of SOA. We conclude that, on a global scale, cloud processing of iOP produces 6.9 Tg of SOA per year or approximately 20% of the total biogenic SOA burden and is the main source of SOA in the mid-troposphere (4 to 6 km).

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Organic aerosol components observed in Northern Hemispheric datasets from Aerosol Mass Spectrometry

Atmospheric Chemistry and Physics ◽

10.5194/acp-10-4625-2010 ◽

2010 ◽

Vol 10 (10) ◽

pp. 4625-4641 ◽

Cited By ~ 677

Author(s):

N. L. Ng ◽

M. R. Canagaratna ◽

Q. Zhang ◽

J. L. Jimenez ◽

J. Tian ◽

...

Keyword(s):

Mass Spectrum ◽

Organic Aerosol ◽

Total Signal ◽

Mass Spectral ◽

Aerosol Mass ◽

Aerosol Mass Spectrometry ◽

Wide Range ◽

Triangular Region ◽

Photochemical Aging ◽

Spectral Diagnostic

Abstract. In this study we compile and present results from the factor analysis of 43 Aerosol Mass Spectrometer (AMS) datasets (27 of the datasets are reanalyzed in this work). The components from all sites, when taken together, provide a holistic overview of Northern Hemisphere organic aerosol (OA) and its evolution in the atmosphere. At most sites, the OA can be separated into oxygenated OA (OOA), hydrocarbon-like OA (HOA), and sometimes other components such as biomass burning OA (BBOA). We focus on the OOA components in this work. In many analyses, the OOA can be further deconvolved into low-volatility OOA (LV-OOA) and semi-volatile OOA (SV-OOA). Differences in the mass spectra of these components are characterized in terms of the two main ions m/z 44 (CO2+) and m/z 43 (mostly C2H3O+), which are used to develop a new mass spectral diagnostic for following the aging of OA components in the atmosphere. The LV-OOA component spectra have higher f44 (ratio of m/z 44 to total signal in the component mass spectrum) and lower f43 (ratio of m/z 43 to total signal in the component mass spectrum) than SV-OOA. A wide range of f44 and O:C ratios are observed for both LV-OOA (0.17±0.04, 0.73±0.14) and SV-OOA (0.07±0.04, 0.35±0.14) components, reflecting the fact that there is a continuum of OOA properties in ambient aerosol. The OOA components (OOA, LV-OOA, and SV-OOA) from all sites cluster within a well-defined triangular region in the f44 vs. f43 space, which can be used as a standardized means for comparing and characterizing any OOA components (laboratory or ambient) observed with the AMS. Examination of the OOA components in this triangular space indicates that OOA component spectra become increasingly similar to each other and to fulvic acid and HULIS sample spectra as f44 (a surrogate for O:C and an indicator of photochemical aging) increases. This indicates that ambient OA converges towards highly aged LV-OOA with atmospheric oxidation. The common features of the transformation between SV-OOA and LV-OOA at multiple sites potentially enable a simplified description of the oxidation of OA in the atmosphere. Comparison of laboratory SOA data with ambient OOA indicates that laboratory SOA are more similar to SV-OOA and rarely become as oxidized as ambient LV-OOA, likely due to the higher loadings employed in the experiments and/or limited oxidant exposure in most chamber experiments.

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Hygroscopicity and composition of Alaskan Arctic CCN during April 2008

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-11-21789-2011 ◽

2011 ◽

Vol 11 (8) ◽

pp. 21789-21834

Author(s):

R. H. Moore ◽

R. Bahreini ◽

C. A. Brock ◽

K. D. Froyd ◽

J. Cozic ◽

...

Keyword(s):

Chemical Composition ◽

Cloud Condensation Nuclei ◽

Anthropogenic Pollution ◽

Organic Aerosol ◽

International Polar Year ◽

Mass Spectral ◽

Aerosol Mass ◽

Alaskan Arctic ◽

Air Mass Types ◽

The Individual

Abstract. We present a comprehensive characterization of cloud condensation nuclei (CCN) sampled in the Alaskan Arctic during the 2008 Aerosol, Radiation, and Cloud Processes affecting Arctic Climate (ARCPAC) project, a component of the POLARCAT and International Polar Year (IPY) initiatives. Four distinct air mass types were sampled including relatively pristine Arctic background conditions as well as biomass burning and anthropogenic pollution plumes. Despite differences in chemical composition, inferred aerosol hygroscopicities were fairly invariant and ranged from κ = 0.1–0.3 over the atmospherically-relevant range of water vapor supersaturations studied. Analysis of the individual mass spectral m/z 43 and 44 peaks from an aerosol mass spectrometer show the organic aerosols sampled to be well-oxygenated, consistent with with long-range transport and aerosol aging processes. However, inferred hygroscopicities are less than would be predicted based on previous parameterizations of biogenic oxygenated organic aerosol, suggesting an upper limit on organic aerosol hygroscopicity above which κ is less sensitive to the O:C ratio. Most Arctic aerosol act as CCN above 0.1 % supersaturation, although the data suggest the presence of an externally-mixed, non-CCN-active mode comprising approximately 0–20 % of the aerosol number. CCN closure was assessed using measured size distributions, bulk chemical composition measurements, and assumed aerosol mixing states; CCN predictions tended toward overprediction, with the best agreement (± 0–20 %) obtained by assuming the aerosol to be externally-mixed with soluble organics. Closure also varied with CCN concentration, and the best agreement was found for CCN concentrations above 100 cm−3 with a 1.5- to 3-fold overprediction at lower concentrations.

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Linking marine phytoplankton emissions, meteorological processes, and downwind particle properties with FLEXPART

Atmospheric Chemistry and Physics ◽

10.5194/acp-21-831-2021 ◽

2021 ◽

Vol 21 (2) ◽

pp. 831-851

Author(s):

Kevin J. Sanchez ◽

Bo Zhang ◽

Hongyu Liu ◽

Georges Saliba ◽

Chia-Li Chen ◽

...

Keyword(s):

Wind Speed ◽

Residence Time ◽

Organic Aerosol ◽

Marine Phytoplankton ◽

Meteorological Variables ◽

Bacterial Degradation ◽

Marine Aerosol ◽

Air Mass ◽

Particle Properties ◽

Aerosol Mass

Abstract. Marine biogenic particle contributions to atmospheric aerosol concentrations are not well understood though they are important for determining cloud optical and cloud-nucleating properties. Here we examine the relationship between marine aerosol measurements (with satellites and model fields of ocean biology) and meteorological variables during the North Atlantic Aerosols and Marine Ecosystems Study (NAAMES). NAAMES consisted of four field campaigns between November 2015 and April 2018 that aligned with the four major phases of the annual phytoplankton bloom cycle. The FLEXible PARTicle (FLEXPART) Lagrangian particle dispersion model is used to spatiotemporally connect these variables to ship-based aerosol and dimethyl sulfide (DMS) observations. We find that correlations between some aerosol measurements with satellite-measured and modeled variables increase with increasing trajectory length, indicating that biological and meteorological processes over the air mass history are influential for measured particle properties and that using only spatially coincident data would miss correlative connections that are lagged in time. In particular, the marine non-refractory organic aerosol mass correlates with modeled marine net primary production when weighted by 5 d air mass trajectory residence time (r=0.62). This result indicates that non-refractory organic aerosol mass is influenced by biogenic volatile organic compound (VOC) emissions that are typically produced through bacterial degradation of dissolved organic matter, zooplankton grazing on marine phytoplankton, and as a by-product of photosynthesis by phytoplankton stocks during advection into the region. This is further supported by the correlation of non-refractory organic mass with 2 d residence-time-weighted chlorophyll a (r=0.39), a proxy for phytoplankton abundance, and 5 d residence-time-weighted downward shortwave forcing (r=0.58), a requirement for photosynthesis. In contrast, DMS (formed through biological processes in the seawater) and primary marine aerosol (PMA) concentrations showed better correlations with explanatory biological and meteorological variables weighted with shorter air mass residence times, which reflects their localized origin as primary emissions. Aerosol submicron number and mass negatively correlate with sea surface wind speed. The negative correlation is attributed to enhanced PMA concentrations under higher wind speed conditions. We hypothesized that the elevated total particle surface area associated with high PMA concentrations leads to enhanced rates of condensation of VOC oxidation products onto PMA. Given the high deposition velocity of PMA relative to submicron aerosol, PMA can limit the accumulation of secondary aerosol mass. This study provides observational evidence for connections between marine aerosols and underlying ocean biology through complex secondary formation processes, emphasizing the need to consider air mass history in future analyses.

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Single-particle measurements of bouncing particles and in situ collection efficiency from an airborne aerosol mass spectrometer (AMS) with light-scattering detection

Atmospheric Measurement Techniques ◽

10.5194/amt-10-3801-2017 ◽

2017 ◽

Vol 10 (10) ◽

pp. 3801-3820 ◽

Cited By ~ 6

Author(s):

Jin Liao ◽

Charles A. Brock ◽

Daniel M. Murphy ◽

Donna T. Sueper ◽

André Welti ◽

...

Keyword(s):

Light Scattering ◽

Mass Spectrometer ◽

Single Particle ◽

Total Mass ◽

Mass Spectra ◽

Collection Efficiency ◽

Aerosol Mass Spectrometer ◽

Mass Spectral ◽

Aerosol Mass ◽

Spectral Signal

Abstract. A light-scattering module was coupled to an airborne, compact time-of-flight aerosol mass spectrometer (LS-AMS) to investigate collection efficiency (CE) while obtaining nonrefractory aerosol chemical composition measurements during the Southeast Nexus (SENEX) campaign. In this instrument, particles scatter light from an internal laser beam and trigger saving individual particle mass spectra. Nearly all of the single-particle data with mass spectra that were triggered by scattered light signals were from particles larger than ∼ 280 nm in vacuum aerodynamic diameter. Over 33 000 particles are characterized as either prompt (27 %), delayed (15 %), or null (58 %), according to the time and intensity of their total mass spectral signals. The particle mass from single-particle spectra is proportional to that derived from the light-scattering diameter (dva-LS) but not to that from the particle time-of-flight (PToF) diameter (dva-MS) from the time of the maximum mass spectral signal. The total mass spectral signal from delayed particles was about 80 % of that from prompt ones for the same dva-LS. Both field and laboratory data indicate that the relative intensities of various ions in the prompt spectra show more fragmentation compared to the delayed spectra. The particles with a delayed mass spectral signal likely bounced off the vaporizer and vaporized later on another surface within the confines of the ionization source. Because delayed particles are detected by the mass spectrometer later than expected from their dva-LS size, they can affect the interpretation of particle size (PToF) mass distributions, especially at larger sizes. The CE, measured by the average number or mass fractions of particles optically detected that had measurable mass spectra, varied significantly (0.2–0.9) in different air masses. The measured CE agreed well with a previous parameterization when CE > 0.5 for acidic particles but was sometimes lower than the minimum parameterized CE of 0.5.

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Impact of Aerosol-Cloud Cycling on Aqueous Secondary Organic Aerosol Formation

Atmosphere ◽

10.3390/atmos10110666 ◽

2019 ◽

Vol 10 (11) ◽

pp. 666 ◽

Cited By ~ 3

Author(s):

William G. Tsui ◽

Joseph L. Woo ◽

V. Faye McNeill

Keyword(s):

Atmospheric Aerosols ◽

Organic Material ◽

Organic Aerosol ◽

Time Of Day ◽

Aerosol Formation ◽

Atmospheric Models ◽

Cloud Processing ◽

Aerosol Mass ◽

Phase Chemistry ◽

The Impact

Chemical processing of organic material in aqueous atmospheric aerosols and cloudwater is known to form secondary organic aerosols (SOA), although the extent to which each of these processes contributes to total aerosol mass is unclear. In this study, we use GAMMA 5.0, a photochemical box model with coupled gas and aqueous-phase chemistry, to consider the impact of aqueous organic reactions in both aqueous aerosols and clouds on isoprene epoxydiol (IEPOX) SOA over a range of pH for both aqueous phases, including cycling between cloud and aerosol within a single simulation. Low pH aqueous aerosol, in the absence of organic coatings or other morphology which may limit uptake of IEPOX, is found to be an efficient source of IEPOX SOA, consistent with previous work. Cloudwater at pH 4 or lower is also found to be a potentially significant source of IEPOX SOA. This phenomenon is primarily attributed to the relatively high uptake of IEPOX to clouds as a result of higher water content in clouds as compared with aerosol. For more acidic cloudwater, the aqueous organic material is comprised primarily of IEPOX SOA and lower-volatility organic acids. Both cloudwater pH and the time of day or sequence of aerosol-to-cloud or cloud-to-aerosol transitions impacted final aqueous SOA mass and composition in the simulations. The potential significance of cloud processing as a contributor to IEPOX SOA production could account for discrepancies between predicted IEPOX SOA mass from atmospheric models and measured ambient IEPOX SOA mass, or observations of IEPOX SOA in locations where mass transfer limitations are expected in aerosol particles.

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