scholarly journals Impact of dry intrusion events on the composition and mixing state of particles during the winter Aerosol and Cloud Experiment in the Eastern North Atlantic (ACE-ENA)

2021 ◽  
Vol 21 (24) ◽  
pp. 18123-18146
Author(s):  
Jay M. Tomlin ◽  
Kevin A. Jankowski ◽  
Daniel P. Veghte ◽  
Swarup China ◽  
Peiwen Wang ◽  
...  
Keyword(s):  
Long Range ◽  
North Atlantic ◽  
Cloud Condensation Nuclei ◽  
Aerosol Size Distribution ◽  
Condensation Nuclei ◽  
Mixing State ◽  
Carbonaceous Particles ◽  
X Ray ◽  
Eastern North Atlantic ◽  
Individual Particles

Abstract. Long-range transport of continental emissions has a far-reaching influence over remote regions, resulting in substantial change in the size, morphology, and composition of the local aerosol population and cloud condensation nuclei (CCN) budget. Here, we investigate the physicochemical properties of atmospheric particles collected on board a research aircraft flown over the Azores during the winter 2018 Aerosol and Cloud Experiment in the Eastern North Atlantic (ACE-ENA) campaign. Particles were collected within the marine boundary layer (MBL) and free troposphere (FT) after long-range atmospheric transport episodes facilitated by dry intrusion (DI) events. Chemical and physical properties of individual particles were investigated using complementary capabilities of computer-controlled scanning electron microscopy and X-ray spectromicroscopy to probe particle external and internal mixing state characteristics. Furthermore, real-time measurements of aerosol size distribution, cloud condensation nuclei (CCN) concentration, and back-trajectory calculations were utilized to help bring into context the findings from offline spectromicroscopy analysis. While carbonaceous particles were found to be the dominant particle type in the region, changes in the percent contribution of organics across the particle population (i.e., external mixing) shifted from 68 % to 43 % in the MBL and from 92 % to 46 % in FT samples during DI events. This change in carbonaceous contribution is counterbalanced by the increase in inorganics from 32 % to 57 % in the MBL and 8 % to 55 % in FT. The quantification of the organic volume fraction (OVF) of individual particles derived from X-ray spectromicroscopy, which relates to the multi-component internal composition of individual particles, showed a factor of 2.06 ± 0.16 and 1.11 ± 0.04 increase in the MBL and FT, respectively, among DI samples. We show that supplying particle OVF into the κ-Köhler equation can be used as a good approximation of field-measured in situ CCN concentrations. We also report changes in the κ values in the MBL from κMBL, non-DI=0.48 to κMBL, DI=0.41, while changes in the FT result in κFT, non-DI=0.36 to κFT, DI=0.33, which is consistent with enhancements in OVF followed by the DI episodes. Our observations suggest that entrainment of particles from long-range continental sources alters the mixing state population and CCN properties of aerosol in the region. The work presented here provides field observation data that can inform atmospheric models that simulate sources and particle composition in the eastern North Atlantic.

scholarly journals Impact of Dry Intrusion Events on Composition and Mixing State of Particles During Winter ACE-ENA Study

2021 ◽  
Author(s):  
Jay M. Tomlin ◽  
Kevin A. Jankowski ◽  
Daniel P. Veghte ◽  
Swarup China ◽  
Peiwen Wang ◽  
...  
Keyword(s):  
Long Range ◽  
North Atlantic ◽  
Cloud Condensation Nuclei ◽  
Aerosol Size Distribution ◽  
Condensation Nuclei ◽  
Mixing State ◽  
Carbonaceous Particles ◽  
X Ray ◽  
Eastern North Atlantic ◽  
Individual Particles

Abstract. Long-range transport of continental emission has far reaching influence over remote regions resulting in substantial change in the size, morphology, and composition of the local aerosol population and cloud condensation nuclei (CCN) budget. Here, we investigate the physiochemical properties of atmospheric particles collected onboard a research aircraft flown over the Azores during the winter 2018 Aerosol and Cloud Experiment in the Eastern North Atlantic (ACE-ENA) campaign. Particles were collected within the marine boundary layer (MBL) and free troposphere (FT), after long-range atmospheric transport episodes facilitated by dry intrusion (DI) events. Chemical and physical properties of individual particles were investigated using complementary capabilities of computer-controlled scanning electron microscopy and X-ray spectro-microscopy to probe particle external and internal mixing state characteristics in the context of real-time measurements of aerosol size distribution, cloud condensation nuclei (CCN) concentration, and back trajectory calculations. While carbonaceous particles were found to be the dominant particle-type in the region, changes in the percent contribution of organics across the particle population (i.e., external mixing) shifted from 68 % to 43 % in the MBL and from 92 % to 46 % in FT samples during DI events. This change in carbonaceous contribution is counterbalanced by the increase of inorganics from 32 % to 57 % in the MBL and 8 % to 55 % in FT. The quantification of organic volume fraction (OVF) of individual particles derived from X-ray spectro-microscopy, which relates to the multi-component internal composition of individual particles, showed a factor of 2.06 ± 0.16 and 1.11 ± 0.04 increase in the MBL and FT, respectively, among DI samples. We show that supplying particle OVF into the κ-Köhler equation can be used as a good approximation of field measured in-situ CCN concentrations. We also report changes in the κ values between κMBL, non-DI = 0.48 to κMBL, DI = 0.41 and κFT, non-DI = 0.36 to κFT, DI = 0.33, which is consistent with enhancements in OVF followed by the DI episodes. Our observations suggest that entrainment of particles from long-range continental sources alters the mixing state population and CCN properties of aerosol in the region. The work presented here provides field observation data that can inform atmospheric models that simulate sources and particle composition in the Eastern North Atlantic.

scholarly journals Marine boundary layer aerosol in Eastern North Atlantic: seasonal variations and key controlling processes

2018 ◽  
Author(s):  
Guangjie Zheng ◽  
Yang Wang ◽  
Allison C. Aiken ◽  
Francesca Gallo ◽  
Mike Jensen ◽  
...  
Keyword(s):  
Boundary Layer ◽  
North Atlantic ◽  
Seasonal Variations ◽  
Dimethyl Sulfide ◽  
Marine Boundary Layer ◽  
Cloud Condensation Nuclei ◽  
Sulfide Oxidation ◽  
Aerosol Size Distribution ◽  
Eastern North Atlantic ◽  
Aerosol Properties

Abstract. The response of marine low cloud systems to changes in aerosol concentration represents one of the largest uncertainties in climate simulations. Major contributions to this uncertainty derive from poor understanding of aerosol under natural conditions and the perturbation by anthropogenic emissions. The Eastern North Atlantic (ENA) is a region of persistent but diverse marine boundary layer (MBL) clouds, whose albedo and precipitation are highly susceptible to perturbations in aerosol properties. In this study, we examine MBL aerosol properties, trace gas mixing ratios, and meteorological parameters measured at the Atmospheric Radiation Measurement Climate Research Facility’s ENA site on Graciosa Island, Azores, Portugal from 2015 to 2017. Measurements impacted by local pollutions on Graciosa Island and during occasional intense biomass burning and dust events are excluded from this analysis. Submicron aerosol size distribution typically consists of three modes: Aitken (At), Accumulation (Ac), and Larger Accumulation (LA) modes, with average number concentrations (denoted as NAt, NAc and NLA below) of 330, 114, and 14 cm−3, respectively. NAt, NAc and NLA show contrasting seasonal variations, suggesting different sources and removal processes. NLA is dominated by sea spray aerosol (SSA), and is higher in winter and lower in summer. This is due to the seasonal variations of SSA production, coalescence scavenging, and dilution by entrained free troposphere (FT) air. In comparison, SSA typically contributes a relatively minor fraction to NAt (10 %) and NAc (21 %) on an annual basis. In addition to SSA, sources of Ac mode particles include entrainment of FT aerosols and condensation growth of At mode particles inside MBL, while coalescence scavenging is the major sink of NAc. The observed seasonal variation of NAc, being higher in summer and lower in winter, generally agrees with the estimate based on the major sources and sink. NAt is mainly controlled by entrainment of FT aerosol, coagulation loss, and growth of At mode particles into Ac mode size range. Our calculation suggests besides the direct contribution from entrained FT Ac mode particles, growth of entrained FT At mode particles in the MBL also represent a substantial source of cloud condensation nuclei (CCN), with the highest contribution potentially reaching nearly 60 % during summer. The growth of At mode particles to CCN size is expected a result of the condensation of sulfuric acid from dimethyl sulfide oxidation, suggesting that ocean ecosystems may have a substantial influence on MBL CCN populations in ENA.

scholarly journals Properties of cloud condensation nuclei (CCN) in the trade wind marine boundary layer of the western North Atlantic

2016 ◽  
Vol 16 (4) ◽  
pp. 2675-2688 ◽  
Author(s):  
Thomas B. Kristensen ◽  
Thomas Müller ◽  
Konrad Kandler ◽  
Nathalie Benker ◽  
Markus Hartmann ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Long Range ◽  
North Atlantic ◽  
Particle Number ◽  
Marine Boundary Layer ◽  
Mineral Dust ◽  
Cloud Condensation Nuclei ◽  
Sea Salt ◽  
Condensation Nuclei ◽  
Accumulation Mode

Abstract. Cloud optical properties in the trade winds over the eastern Caribbean Sea have been shown to be sensitive to cloud condensation nuclei (CCN) concentrations. The objective of the current study was to investigate the CCN properties in the marine boundary layer (MBL) in the tropical western North Atlantic, in order to assess the respective roles of inorganic sulfate, organic species, long-range transported mineral dust and sea-salt particles. Measurements were carried out in June–July 2013, on the east coast of Barbados, and included CCN number concentrations, particle number size distributions and offline analysis of sampled particulate matter (PM) and sampled accumulation mode particles for an investigation of composition and mixing state with transmission electron microscopy (TEM) in combination with energy-dispersive X-ray spectroscopy (EDX). During most of the campaign, significant mass concentrations of long-range transported mineral dust was present in the PM, and influence from local island sources can be ruled out. The CCN and particle number concentrations were similar to what can be expected in pristine marine environments. The hygroscopicity parameter κ was inferred, and values in the range 0.2–0.5 were found during most of the campaign, with similar values for the Aitken and the accumulation mode. The accumulation mode particles studied with TEM were dominated by non-refractory material, and concentrations of mineral dust, sea salt and soot were too small to influence the CCN properties. It is highly likely that the CCN were dominated by a mixture of sulfate species and organic compounds.

scholarly journals On aerosol hygroscopicity, cloud condensation nuclei (CCN) spectra and critical supersaturation measured at two remote islands of Korea between 2006 and 2009

2011 ◽  
Vol 11 (24) ◽  
pp. 12627-12645 ◽  
Author(s):  
J. H. Kim ◽  
S. S. Yum ◽  
S. Shim ◽  
S.-C. Yoon ◽  
J. G. Hudson ◽  
...  
Keyword(s):  
Korean Peninsula ◽  
Total Concentration ◽  
Cloud Condensation Nuclei ◽  
Geometric Mean ◽  
Aerosol Size Distribution ◽  
Monitoring Site ◽  
Hygroscopic Growth ◽  
Condensation Nuclei ◽  
Critical Supersaturation ◽  
Better Than

Abstract. Aerosol size distribution, total concentration (i.e. condensation nuclei (CN) concentration, NCN), cloud condensation nuclei (CCN) concentration (NCCN), hygroscopicity at ~90% relative humidity (RH) were measured at a background monitoring site at Gosan, Jeju Island, south of the Korean Peninsula in August 2006, April to May 2007 and August to October 2008. Similar measurements took place in August 2009 at another background site (Baengnyeongdo Comprehensive Monitoring Observatory, BCMO) on the island of Baengnyeongdo, off the west coast of the Korean Peninsula. Both islands were found to be influenced by continental sources regardless of season and year. Average values for all of the measured NCCN at 0.2, 0.6 and 1.0% supersaturations (S), NCN, and geometric mean diameter (Dg) from both islands were in the range of 1043–3051 cm−3, 2076–4360 cm−3, 2713–4694 cm−3, 3890–5117 cm−3 and 81–98 nm, respectively. Although the differences in Dg and NCN were small between Gosan and BCMO, NCCN at various S was much higher at the latter, which is closer to China. Most of the aerosols were internally mixed and no notable differences in hygroscopicity were found between the days of strong pollution influence and the non-pollution days for both islands. During the 2008 and 2009 campaigns, critical supersaturation for CCN nucleation (Sc) for selected particle sizes was measured. Particles of 100 nm diameters had mean Sc of 0.19 ± 0.02% during 2008 and those of 81 and 110 nm diameters had mean Sc of 0.26 ± 0.07% and 0.17 ± 0.04%, respectively, during 2009. The values of the hygroscopicity parameter (κ), estimated from measured Sc, were mostly higher than the κ values obtained from the measured hygroscopic growth at ~90% RH. For the 2008 campaign, NCCN at 0.2, 0.6 and 1.0% S were predicted based on measured dry particle size distributions and various ways of representing particle hygroscopicity. The best closure was obtained when temporally varying and size-resolved hygroscopicity information from the HTDMA was used, for which the average relative deviations from the measured values were 28 ± 20% for 0.2% S (mostly under-prediction), 25 ± 52% for 0.6% (balanced between over- and under-prediction) and 19 ± 15% for 1.0% S (balanced). Prescribing a constant hygroscopicity parameter suggested in the literature (κ = 0.3) for all sizes and times resulted in average relative deviations of 28–41% where over-prediction was dominant. When constant hygroscopicity was assumed, the relative deviation tended to increase with decreasing NCCN, which was accompanied by an increase of the sub-100 nm fraction. These results suggest that hygroscopicity information for particles of diameters smaller than 100 nm is crucial for more accurate predictions of NCCN. For confirmation when κ = 0.17, the average κ for sub-100 nm particles in this study, was applied for sub-100 nm and κ = 0.3 for all other sizes, the CCN closure became significantly better than that with κ = 0.3 for all sizes.

scholarly journals Measured and modelled Cloud Condensation Nuclei (CCN) concentration in São Paulo, Brazil: the importance of aerosol size-resolved chemical composition on CCN concentration prediction

2013 ◽  
Vol 13 (12) ◽  
pp. 32353-32389 ◽  
Author(s):  
G. P. Almeida ◽  
J. Brito ◽  
C. A. Morales ◽  
M. F. Andrade ◽  
P. Artaxo
Keyword(s):  
Chemical Composition ◽  
Real Time ◽  
Cloud Condensation Nuclei ◽  
Bulk Composition ◽  
Sao Paulo ◽  
Aerosol Size Distribution ◽  
São Paulo ◽  
Condensation Nuclei ◽  
Aerosol Composition ◽  
The Impact

Abstract. Measurements of cloud condensation nuclei (CCN), aerosol size distribution and non-refractory chemical composition were performed from 16 to 31 October 2012 in the São Paulo Metropolitan Area (SPMA), Brazil. CCN measurements were performed at 0.2%, 0.4%, 0.6%, 0.8% and 1.0% water supersaturation and were subsequently compared with Köhler theory, considering the chemical composition. Real-time chemical composition has been obtained deploying for the first time in SPMA an Aerosol Chemical Ionization Monitor (ACSM). CCN closure analyses were performed considering internal mixture. Average aerosol composition during the studied period yielded 4.81 ± 3.05, 3.26 ± 2.10, 0.30 ± 0.27, 0.52 ± 0.32, 0.37 ± 0.21 and 0.04 ± 0.04 μg m−3 for organics, BC, NH4, SO4, NO3 and Cl, respectively. Particle number concentration was 12 813 ± 5350 cm−3, being a large fraction in the nucleation mode. CCN concentrations were on average 1090 ± 328 cm−3 and 3570 ± 1695 cm−3 at SS = 0.2% and SS = 1.0%, respectively. Results show an increase in aerosol hygroscopicity in the afternoon as a result of aerosol photochemical processing, leading to an enhancement of both organic and inorganic secondary aerosols in the atmosphere, as well as an increase in aerosol average diameter. Considering the bulk composition alone, CCN concentrations were substantially overpredicted (29.6 ± 45.1% at 0.2% supersaturation and 57.3 ± 30.0% at 1.0% supersaturation). Overall, the impact of composition on the calculated NCCN decreases with decreasing supersaturation, partially because using bulk composition introduces less bias for large diameters and lower critical supersaturations. Results suggest that the consideration of only inorganic fraction improves the calculated NCCN. Introducing a size-dependent chemical composition based on filter measurements from previous campaigns has considerably improved simulated values for NCCN (average overprediction error 3.0 ± 33.4% at 0.20% supersaturation and average under prediction error 2.4 ± 20.5% at 1.0% supersaturation). This study provides the first insight on aerosol real-time composition and hygroscopicity on a~site strongly impacted by emissions of a unique vehicular fleet due to the extensive biofuel usage.

scholarly journals The diverse chemical mixing state of aerosol particles in the southeastern United States

2018 ◽  
Vol 18 (16) ◽  
pp. 12595-12612 ◽  
Author(s):  
Amy L. Bondy ◽  
Daniel Bonanno ◽  
Ryan C. Moffet ◽  
Bingbing Wang ◽  
Alexander Laskin ◽  
...  
Keyword(s):  
Atmospheric Aerosols ◽  
Climate Modeling ◽  
Chemical Species ◽  
Mixing State ◽  
Accumulation Mode ◽  
X Ray ◽  
Scanning Transmission ◽  
Time Periods ◽  
Cloud Activation ◽  
Individual Particles

Abstract. Aerosols in the atmosphere are chemically complex with thousands of chemical species distributed in different proportions across individual particles in an aerosol population. An internal mixing assumption, with species present in the same proportions across all aerosols, is used in many models and calculations of secondary organic aerosol (SOA) formation, cloud activation, and aerosol optical properties. However, many of these effects depend on the distribution of species within individual particles, and important information can be lost when internal mixtures are assumed. Herein, we show that – as found during the Southern Oxidant and Aerosol Study (SOAS) in Centreville, Alabama, at a rural, forested location – aerosols frequently are not purely internally mixed, even in the accumulation mode (0.2–1.0 µm). A range of aerosol sources and the mixing state were determined using computer-controlled scanning electron microscopy with energy-dispersive X-ray spectroscopy (CCSEM-EDX) and scanning transmission X-ray microscopy–near-edge X-ray absorption fine structure spectroscopy (STXM-NEXAFS). Particles that were dominated by SOA and inorganic salts (e.g., ammonium sulfate) were the majority of particles by number fraction from 0.2 to 5 µm with an average of 78 % SOA in the accumulation mode. However, during certain periods contributions by sea spray aerosol (SSA) and mineral dust were significant to accumulation (22 % SSA and 26 % dust) and coarse-mode number concentrations (38 % SSA and 63 % dust). The fraction of particles containing key elements (Na, Mg, K, Ca, and Fe) were determined as a function of size for specific classes of particles. Within internally mixed SOA/sulfate particles < 5 % contained Na, Mg, K, Ca, or Fe, though these nonvolatile cations were present in particles from the other sources (e.g., SSA and dust). Mass estimates of the aerosol elemental components were used to determine the extent of internal versus external mixing by calculating the mixing state index (χ). The aerosol population was more externally mixed than internally mixed during all time periods analyzed. Accumulation mode aerosol ranged from more internally mixed during SOA periods to mostly externally mixed during dust periods. Supermicron aerosols were most externally mixed during SOA time periods, when more SOA particles added a distinct supermicron class, and more internally mixed when dominated by a single particle type (e.g., SSA or dust). These results emphasize that neither external nor internal mixtures fully represent the mixing state of atmospheric aerosols, even in a rural, forested environment, which has important implications for air quality and climate modeling.

scholarly journals Measured and modelled cloud condensation nuclei (CCN) concentration in São Paulo, Brazil: the importance of aerosol size-resolved chemical composition on CCN concentration prediction

2014 ◽  
Vol 14 (14) ◽  
pp. 7559-7572 ◽  
Author(s):  
G. P. Almeida ◽  
J. Brito ◽  
C. A. Morales ◽  
M. F. Andrade ◽  
P. Artaxo
Keyword(s):  
Chemical Composition ◽  
Real Time ◽  
Cloud Condensation Nuclei ◽  
Bulk Composition ◽  
Sao Paulo ◽  
Aerosol Size Distribution ◽  
São Paulo ◽  
Condensation Nuclei ◽  
Kohler Theory ◽  
The Impact

Abstract. Measurements of cloud condensation nuclei (CCN), aerosol size distribution and non-refractory chemical composition were performed from 16 to 31 October 2012 in the São Paulo Metropolitan Area (SPMA), Brazil. CCN measurements were performed at 0.23, 0.45, 0.68, 0.90 and 1.13% water supersaturation and were subsequently compared with the Köhler theory, considering the chemical composition. Real-time chemical composition has been obtained by deploying, for the first time in the SPMA, an aerosol chemical ionization monitor (ACSM). CCN closure analyses were performed considering internal mixtures. Average aerosol composition during the studied period yielded (arithmetic mean~± standard deviation) 4.81 ± 3.05, 3.26 ± 2.10, 0.30 ± 0.27, 0.52 ± 0.32, 0.37 ± 0.21 and 0.04 ± 0.04 μg m−3 for organics, BC, NH4, SO4, NO3 and Cl, respectively. Particle number concentration was 12 813 ± 5350 cm−3, with a dominant nucleation mode. CCN concentrations were on average 1090 ± 328 and 3570 ± 1695 cm−3 at SS = 0.23% and SS = 1.13%, respectively. Results show an increase in aerosol hygroscopicity in the afternoon as a result of aerosol photochemical processing, leading to an enhancement of both organic and inorganic secondary aerosols in the atmosphere, as well as an increase in aerosol average diameter. Considering the bulk composition alone, observed CCN concentrations were substantially overpredicted when compared with the Köhler theory (44.1 ± 47.9% at 0.23% supersaturation and 91.4 ± 40.3% at 1.13% supersaturation). Overall, the impact of composition on the calculated CCN concentration (NCCN) decreases with decreasing supersaturation, partially because using bulk composition introduces less bias for large diameters and lower critical supersaturations, defined as the supersaturation at which the cloud droplet activation will take place. Results suggest that the consideration of only inorganic fraction improves the calculated NCCN. Introducing a size-dependent chemical composition based on filter measurements from previous campaigns has considerably improved simulated values for NCCN (average overprediction error 14.8 ± 38.6% at 0.23% supersaturation and 3.6 ± 21.6% at 1.13% supersaturation). This study provides the first insight on aerosol real-time composition and hygroscopicity at a site strongly impacted by emissions of a unique vehicular fleet due to the extensive biofuel usage.

scholarly journals Marine boundary layer aerosol in the eastern North Atlantic: seasonal variations and key controlling processes

2018 ◽  
Vol 18 (23) ◽  
pp. 17615-17635 ◽  
Author(s):  
Guangjie Zheng ◽  
Yang Wang ◽  
Allison C. Aiken ◽  
Francesca Gallo ◽  
Michael P. Jensen ◽  
...  
Keyword(s):  
Boundary Layer ◽  
North Atlantic ◽  
Seasonal Variations ◽  
Dimethyl Sulfide ◽  
Marine Boundary Layer ◽  
Sulfide Oxidation ◽  
Aerosol Size Distribution ◽  
Eastern North Atlantic ◽  
Aitken Mode ◽  
Aerosol Properties

Abstract. The response of marine low cloud systems to changes in aerosol concentration represents one of the largest uncertainties in climate simulations. Major contributions to this uncertainty are derived from poor understanding of aerosol under natural conditions and the perturbation by anthropogenic emissions. The eastern North Atlantic (ENA) is a region of persistent but diverse marine boundary layer (MBL) clouds, whose albedo and precipitation are highly susceptible to perturbations in aerosol properties. In this study, we examine MBL aerosol properties, trace gas mixing ratios, and meteorological parameters measured at the Atmospheric Radiation Measurement Climate Research Facility's ENA site on Graciosa Island, Azores, Portugal, during a 3-year period from 2015 to 2017. Measurements impacted by local pollution on Graciosa Island and during occasional intense biomass burning and dust events are excluded from this study. Submicron aerosol size distribution typically consists of three modes: Aitken (At, diameter Dp<∼100 nm), accumulation (Ac, Dp within ∼100 to ∼300 nm), and larger accumulation (LA, Dp>∼300 nm) modes, with average number concentrations (denoted as NAt, NAc, and NLA below) of 330, 114, and 14 cm−3, respectively. NAt, NAc, and NLA show contrasting seasonal variations, suggesting different sources and removal processes. NLA is dominated by sea spray aerosol (SSA) and is higher in winter and lower in summer. This is due to the seasonal variations of SSA production, in-cloud coalescence scavenging, and dilution by entrained free troposphere (FT) air. In comparison, SSA typically contributes a relatively minor fraction to NAt (10 %) and NAc (21 %) on an annual basis. In addition to SSA, sources of Ac-mode particles include entrainment of FT aerosols and condensation growth of Aitken-mode particles inside the MBL, while in-cloud coalescence scavenging is the major sink of NAc. The observed seasonal variation of NAc, being higher in summer and lower in winter, generally agrees with the steady-state concentration estimated from major sources and sinks. NAt is mainly controlled by entrainment of FT aerosol, coagulation loss, and growth of Aitken-mode particles into the Ac-mode size range. Our calculation suggests that besides the direct contribution from entrained FT Ac-mode particles, growth of entrained FT Aitken-mode particles in the MBL also represent a substantial source of cloud condensation nuclei (CCN), with the highest contribution potentially reaching 60 % during summer. The growth of Aitken-mode particles to CCN size is an expected result of the condensation of sulfuric acid, a product from dimethyl sulfide oxidation, suggesting that ocean ecosystems may have a substantial influence on MBL CCN populations in the ENA.

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