* What were the major goals of the project?

The principal objective of this proposed study is to characterize size-resolved sub-micron sea-salt particle production.  However, the proposed study will also characterize sub-micron CCN fluxes from/to the surface ocean as a function of meteorological, hydrological and sea water chemical/ biological parameters and airmass origin.  The combination of micrometeorological flux measurements with oceanic whitecap coverage can provide crucial information to modelers interested in sea spray production parameterizations.

* What was accomplished under these goals?

Major Activities:

Scanning mobility particle sizer (SMPS) and the hygroscopicity tandem differential mobility analyzer (HTDMA) system was deployed at the U.S. Army Corps of Engineers Field Research Facility in Duck, North Carolina during fall 2015 and spring 2016.

HTDMA/SMPS system was deployed onboard of NOAA Ship Hi’ialakai June 25, 2016 to July 3, 2016

Continuous flow hygroscopicity-resolved relaxed eddy accumulation (Hy-Res REA) method of measuring size-resolved sodium chloride particle fluxes was deployed inside the US EPA wind tunnel during spring 2017

Continuous flow hygroscopicity-resolved relaxed eddy accumulation (Hy-Res REA) method of measuring size-resolved black carbon particle fluxes were measured off the rooftop of the Jordan building on NC State Campus during fall 2017

Specific Objectives:

Measure size-selected black carbon particle fluxes in an urban environment

Measure size-selected hygroscopicity-resolved sea-salt aerosol fluxes

Characterize sea spray aerosol growth factor (GF)

Characterize sea spray aerosol number size distribution

Elucidate the source of marine boundary layer particles over the regions remote from continental boundaries

Characterize hygroscopicity of particles at the US east coast

Use the Floating Classroom Program to educate citizens about carbon cycle and climate change

Significant Results:

We have designed and built the first instrument capable of measuring hygroscopicity-based, size-resolved particle fluxes using a continuous-flow Hygroscopicity-Resolved Relaxed Eddy Accumulation (Hy-Res REA) technique. The instrument was deployed at at the US Army Corps of Engineers’ FRF in Duck, NC and onboard of NOAA Ship Hi’ialakai to measure size-selected fluxes of sea salt aerosol.The instrument was also deployed rooftop of the building at the NC State Campus in Raleigh, NC to measure size-selected fluxes of black carbon.

We have designed a new algorithm which decomposes hygroscopicity distributions into three classes: carbon-containing particles, sulfate-like particles, and sodium-containing particles. Results from this algorithm showed low and steady sodium-containing particle concentrations while the sulfate-like and carbon-containing particle concentrations varied during the cruise. According to the classification scheme, carbon-containing particles contributed at least 3-7%, sulfate-like particles contributed at most 77-88% and sodium-containing particles at least contributed 9-16% to the total aerosol number concentration. Size distribution and hygroscopicity data, in conjunction with airmass back-trajectory analysis, suggested that the aerosol budget in the subtropical North Pacific MBL may be controlled by aerosol entrainment from the free troposphere.

We have shown that East Coast US sub-micron aerosols mostly contain ammonium sulfate (62% to 83%), with small contributions from carbonaceous particles and sea-salt (up to 37% and 9%, respectively).

* What opportunities for training and professional development has the project provided?

Three graduate students at MS (Brittany Phillips and Taylor Royalty) and one PhD student (Kyle Dawson) were involved in this project. They have learned how to write codes in Matlab and Labview, how to build and operate instruments.

Kyle Dawson, PhD, 2017 (now at NASA Langley Research Center, NASA Postdoctoral Fellowship recipient)

Brittany Phillips, MS, 2017 (now a Product Design Engineer at Denso Manufacturing)

Taylor Royalty, MS, 2017 (now a PhD candidate at the University of Tennessee)

* How have the results been disseminated to communities of interest?

Through this project website:

http://seasaltaerosol.wordpress.ncsu.edu/

Through paper publication in peer-reviewed literature:

1. Jaimes-Correa, J. C., N. Meskhidze, M. D. Petters, T. M. Royalty, and B.N., Phillips. Relative contribution of different sources to ultra-fine particle number budget in the urban environment, in preparation.
2. Phillips, B.N., Royalty, T.M., Dawson, K.W., Reed, R., Petters, M. D., & Meskhidze, N. (2018). Hygroscopicity- and size-resolved measurements of submicron aerosol on the East Coast of the United States. Journal of Geophysical Research: Atmospheres, 123, 1826–1839. https://doi.org/10.1002/2017JD027702
3. Meskhidze, N., T. M. Royalty, B. N. Phillips, K. W. Dawson, M. D. Petters, R. Reeds, J. P. Weinstein, D.A. Hook, and R. W. Wiener (2018), Continuous flow Hygroscopicity-Resolved Relaxed Eddy Accumulation (Hy-Res REA) method of measuring size-resolved sea-salt particle fluxes, Aerosol. Sci. Tech. https://doi.org/10.1080/02786826.2017.1423174.
4. Royalty, T. M., B. N. Phillips, K. W. Dawson, R. Reed, N. Meskhidze, and M. D. Petters (2017), Aerosol Properties Observed in the Subtropical North Pacific Boundary Layer, J. Geophys. Res. Atmos., 122, https://doi.org/10.1002/2017JD026913
5. Dawson, K. W., M. D. Petters, N. Meskhidze, S. Suda Petters, and S. M. Kreidenweis (2016) Hygroscopic growth and cloud droplet activation of marine hydrogels, J. Geophys. Res. Atmos.,121, https://doi.org/10.1002/2016JD025143

Through conference presentations:

1. Jaimes-Correa, J. C., N. Meskhidze, M. Petters, T. M. Royalty, B. N. Phillips, Relative contribution of different sources to ultra-fine particle number budget in the urban environment, AGU Fall meeting, December 10 – 14, 2018, Washington, D.C.
2. Meskhidze, N., T. M. Royalty, B. N. Phillips, K. Dawson, M. D. Petters, R. Reed, J. P. Weinstein, D. A. Hook, R. Wiener, Continuous Flow Hygroscopicity-Resolved Relaxed Eddy Accumulation (Hy-Res REA) Method of Measuring Size-Resolved Sea-Salt Particle Fluxes, AGU Fall meeting, December 11 – 15, 2017, New Orleans, LA.
3. Meskhidze, N., T. M. Royalty, B. N. Phillips, K. Dawson, M. D. Petters, R. Reed, J. P. Weinstein, D. A. Hook, R. Wiener, Continuous Flow Hygroscopicity-Resolved Relaxed Eddy Accumulation (Hy-Res REA) Method of Measuring Size-Resolved Sea-Salt Particle Fluxes, 36th AAAR Annual Conference, October 16 – 20, 2017, Raleigh NC.
4. N. Meskhidze, T. M. Royalty, T. M., B. N. Phillips, K. W. Dawson, M. D. Petters, R. Reed, J. P. Weinstein, D.A. Hook, and R. W. Wiener, Continuous Flow Hygroscopicity-resolved Relaxed Eddy Accumulation (Hy-res REA) Method of Measuring Size-resolved Sea-salt Particle Fluxes, Goldschmidt2017, August 13 – 18, 2017, Paris, France.
5. Meskhidze, N., Constraining sea spray contribution to the marine boundary layer aerosol number concentration, invited keynote presentation at the frontiers in ocean-atmosphere exchange: Air sea interface and fluxes of mass and energy, May 15-18, 2017, Cargèse, Corsica, France.
6. Royalty, T., B. Phillips, K. Dawson, R. Reed and N. Meskhidze, Shipborne measurements of aerosol number size distribution and hygroscopicity over the North Pacific Ocean, poster presentation, AGU Fall meeting, December 12 – 16, 2016, San Francisco, CA.
7. Phillips, B., K. Dawson, T. Royalty, R. Reed, M. D. Petters, and N. Meskhidze, Measurements of Hygroscopicity- and Size-Resolved Sea Spray Aerosol, April 8, 2016, Raleigh, NC.
8. Meskhidze, N., M. D. Petters, R. Reed, K. Dawson, B. Phillips, and T. Royalty, New Instrument for Measuring Size-resolved Submicron Sea Spray Particle Production From Ocean, December 14 – 18, 2015, San Francisco, CA.
9. Phillips, B., K. Dawson, T. Royalty, R. Reed, M. D. Petters, and N. Meskhidze, Measurements of Hygroscopicity- and Size-Resolved Sea Spray Aerosol, December 14 – 18, 2015, San Francisco, CA.
10. Royalty, T., M. D. Petters, A. Grieshop, N. Meskhidze, R. Reed, B. Phillips, and K. Dawson, Aerosol Size, CCN, and Black Carbon Properties at a Coastal Site in the Eastern U.S., December 14 – 18, 2015, San Francisco, CA.
11. B. Phillips, K. Dawson, T. Royalty, R. Reed, M. D. Petters, and N. Meskhidze, A novel instrument to measure hygroscopicity- and size-resolved particle fluxes, Community Modeling and Analysis System (CMAS), October 5–7, 2015, Chapel Hill, NC.
12. Meskhidze, N., M. D. Petters, R. E. Reed, K. Dawson, and B. Phillips, New instrument for measuring size-resolved submicron sea-salt particle production from ocean, 95th AMS Annual Meeting, 4–8 January 2015, Phoenix, AZ.
13. Dawson, K., M. D. Petters, and N. Meskhidze, Hygroscopic growth and cloud droplet activation of marine hydrogels, oral presentation, 95th AMS Annual Meeting, 4–8 January 2015, Phoenix, AZ.
14. Meskhidze, N., K. Dawson, S. Suda, M. Petters, New Insights For Marine Source Organics: Laboratory Measurements, Remote Sensing & Model Results, invited presentation at the New Insights into Gas-Phase Atmospheric Chemistry conference, July 28-August 1, 2014, Telluride, CO.
15. Meskhidze, N. (2015) The Importance of Marine Aerosols for Climate Change Assessments, in Integrated Land-use Management Modelling of Black Sea Estuaries (ILMM-BSE) Project Implemented with the financial assistance of European Union in the framework of Black Sea Basin Joint Operational Program 2007-2013, popular article.

Journals or Juried Conference Papers

• N. Phillips, T. M. Royalty, K. W. Dawson, R. Reed, M. D. Petters, and N. Meskhidze (2018). Hygroscopicity- and size-resolved measurements of submicron aerosol on the East Coast of the United States.  J. Geophys. Res. Atmospheres.   . Status = PUBLISHED; Acknowledgment of Federal Support = Yes
• Dawson, K. W., M. D. Petters, N. Meskhidze, S. Suda Petters, and S. M. Kreidenweis (2016). Hygroscopic growth and cloud droplet activation of marine hydrogels.   Geophys. Res. Atmos.   . Status = PUBLISHED; Acknowledgment of Federal Support = Yes ; Peer Reviewed = Yes
• Jaimes-Correa, J. C., N. Meskhidze, M. D. Petters, T. M. Royalty, and B.N., Phillips (). Relative contribution of different sources to ultra-fine particle number budget in the urban environment.  Geophys. Res. Atmospheres.   . Status = OTHER; Acknowledgment of Federal Support = Yes
• Meskhidze, T. M. Royalty, B. N. Phillips, K. W. Dawson, M. D. Petters, R. Reed, J. P. Weinstein, D. A. Hook, and R. W. Wiener (2018). Continuous flow Hygroscopicity-Resolved Relaxed Eddy Accumulation (Hy-Res REA) method of measuring size-resolved sea-salt particle fluxes.  Aerosol Sci. and Technol..   . Status = PUBLISHED; Acknowledgment of Federal Support = Yes
• M. Royalty, B. N. Phillips, K. W. Dawson, R. Reed, N. Meskhidze, and M. D. Petters (2017). Aerosol Properties Observed in the Subtropical North Pacific Boundary Layer.  J. Geophys. Rev. Atmospheres.   . Status = PUBLISHED; Acknowledgment of Federal Support = Yes

Impacts

What is the impact on the development of the principal discipline(s) of the project?

In this study, we have built the instrument capable of making size- and hygroscopicity-resolved aerosol flux measurements. We have also developed a new methodology for measuring particle fluxes in the atmosphere: a continuous flow hygroscopicity-resolved relaxed eddy accumulation technique. The instrument was tested inside the EPA wind tunnel using sodium chloride (NaCl) and ammonium sulfate (AS) particles. NaCl particle fluxes measured by REA technique were compared against the eddy covariance (EC) turbulent flux measurements. A linear relationship was found for the flux values measured by two different techniques. Using the ratio of the two fluxes, the factor was derived, which agreed favorably with the value calculated through theoretical formulations. Overall, this study showed that the instrument resulted in unbiased particle flux measurements with the NaCl detection limit of 3 × 10⁵and classification limit of 6 × 10⁵ m⁻²s⁻¹. The data analysis shows that when the instrument is tuned to measure NaCl particle fluxes (i.e., using a κ ∼1.3), the continuous flow hygroscopicity-resolved relaxed eddy accumulation (Hy-Res REA) technique is able to achieve an order of magnitude separation between the NaCl and AS particle fluxes of similar magnitude. The NaCl detection limit of the instrument is within the range of current parameterizations estimates for 100 nm dry NaCl particles production flux from 3 × 10⁴ to 2 × 10⁶m⁻²s⁻¹ for the near-surface wind speed of 8 m s⁻¹.

We have also developed a new instrument, a “ship simulator”. This new instrument consists of two actuators and a power supply mounted on a platform. The actuators can move sonic anemometer in different directions with the prescribed frequency. The platform is intended for testing a software designed for removing the fluctuating velocity that is due to the ship motion before making a decision on up/down fluxes. We have written a software (in Matlab) that is capable of correcting instantaneous: 1) Tilt of the anemometer due to variations in pitch, roll, yaw, and heading; 2) Angular velocities at the anemometer due to rotation of the ship about its local coordinate system axes; and 3) Translational velocities of the platform with respect to a fixed frame of reference. The software communicates with the Inertial Measurement Unit (IMU), 4^thgeneration addition to the Motion Trackers of Xsens, mounted on top of the sonic anemometer. The IMU consists of gyroscopes, accelerometers, magnetometer, barometer, and a GPS receiver. The motion correction system (comprised of the IMU, sonic anemometer, and in-house software) was tested on board of NOAA Ship Hi’ialakai. The results compared well with the established motion correction sensors. The new motion correction sensor makes it possible to deploy Hy-Res REA system on a ship.

What is the impact on other disciplines?

The new instrument using a continuous-flow Hygroscopicity-Resolved Relaxed Eddy Accumulation (Hy-Res REA) technique for measuring sea-salt fluxes is expected to lead to improved characterization of sea spray source terms and the marine boundary layer CCN budget.

What is the impact on the development of human resources?

This project provided research opportunities for undergraduate students (John Hader, David Harley), promoted graduate education and training (Kyle Dawson, Brittany Phillips, Taylor Royalty, Rachel Coons), and introduced local high school students to basic atmospheric and oceanic science principles.

What is the impact on physical resources that form infrastructure?

Two hygroscopicity tandem differential mobility analyzers (HTDMA) and thermodenuder purchased as part of the relaxed eddy accumulation (REA) system and the IMU sensor purchased as part of the motion correction system contribute significantly to the available infrastructure of our laboratory.

What is the impact on institutional resources that form infrastructure?

Equipment purchased through this grant will be available for other researchers within our university, that way contributing to institutional resources.

What is the impact on society beyond science and technology?

The number concentration and chemical composition of 50 to 200 nm diameter sea spray particles are critical to regional and global climate models.  Large discrepancies between the studies can perhaps be reconciled for improved representation of marine boundary layer CCN budgets. Explicit separation of sub-micron sea-salt production fluxes from the rest of sea spray particles would likely reduce current (often more than two orders of magnitude) uncertainty in parameterizations of size-dependent sea spray production fluxes.

Changes/Problems

Changes in approach and reason for change

Thermodenuders initially proposed for characterization of sea spray aerosol were substituted by the Hygroscopicity Classification Algorithm developed in Royalty et al. (2017).

Actual or Anticipated problems or delays and actions or plans to resolve them

Two no-cost extensions were requested in this study.

There were two major causes for the delay: 1. The absence of anticipated considerable vertical gradient in sub-micron sea spray number concentration (i.e., the presence of the clear source at the ocean surface); and 2. The difficulty with using thermodenuders.

1. When the project was started 5 years ago, there was a common knowledge that sea spray contributes a considerable fraction of sub-micron aerosol number concentration in the remote marine boundary layer. However, our study showed that sea spray contributes a minor fraction of submicron number in the marine boundary layer. This made it impossible to test the flux measurement system over the ocean. To show the capability of the instrument for the measuring sea salt fluxes, the experiment was carried out inside the US EPA wind tunnel.
2. After spending more than 6 months characterizing the thermodenuders and in light of the recent paper by [Rasmussen et al., 2017] that shows that the large fraction of volatility change of seawater could be due to decomposition of hydrates in the thermodenuder, we acknowledged that thermodenuders were not suitable for sea salt characterization. We proposed to supplement thermodenuders by the new kernel fractionation method proposed by Royalty et al.[2017]. We have shown (the paper in preparation) that this new method allows for measurement of size-resolved black carbon concentration.

The project focuses on the development and usage of a novel measurement technique to resolve critical issues in the formation of sub-micron sea-salt particles from the ocean bubble bursting process.

Marine aerosols play an important role in controlling the Earth’s radiation balance, cloud formation and microphysical properties, and the chemistry of the marine atmosphere.  An accurate knowledge of size and composition dependent production flux of primary sea spray aerosol is also important for correct assessment of the role of man-made aerosols in climate change, since observations only constrain the net forcing of aerosols (anthropogenic + natural) and the global model-predicted radiative effects are shown to be very sensitive to prescribed/diagnosed number-size distribution of background aerosols.

One particular knowledge gap preventing improved assessments of marine aerosol emissions lays in the yet uncharacterized contribution of sea-salt to the cloud condensation nuclei (CCN) budget over the marine boundary layer (MBL).

Studies radically differ in their description of the chemical composition of sea spray in 50 to 200 nm range. In this particle size range, most critical to the climate models, studies differ in their description of the chemical composition of sea spray particles as the purely organic, purely sea-salt or mixture of both.

The absence of precise information regarding the size dependent production flux of sea-salt particles prevents modelers from explaining discrepancies between model-predicted and measured CCN number concentration in the MBL.

Here we argue that if one succeeds in measuring the size and composition dependent production flux of primary sea spray particles as a function of meteorological, hydrological and ocean chemical/biological properties that can significantly improve aerosol source functions available for regional and global climate models.

Proposed Research

We propose to deploy a relaxed eddy accumulation (REA) flux system specifically designed to measure turbulent fluxes of size-resolved dry sea-salt cores (REA-S flux system). The main principle of the REA-S flux system is based on the humidified tandem differential mobility analyzer (HTDMA) technique, which segregates particles according to their hygroscopic growth factors. Having a unique growth factor will allow pure sea-salt particles to be segregated from all other aerosols.

Knowledge of sub-micron sea-salt number emissions is crucial to isolate the importance of ocean primary particle formation from continental/anthropogenic aerosols entrained from the free troposphere, nucleation from the gas phase oxidation of dimethylsulfide (DMS) or marine secondary organic aerosol (SOA) production from ocean emitted biogenic volatile organic compounds (BVOCs).

The REA-S flux system will be deployed at the 560 m long research pier near the town of Duck, NC. Previous studies showed that during onshore winds the sea spray flux measurements at the site are representative of open ocean conditions. The experiment matrix will be designed to cover a range of conditions and processes including different wind speeds, aerosol sizes selected for the flux measurements, seawater chemical and biological composition.

The intellectual merit of this proposal lies in the novel technique for measuring turbulent fluxes of size-resolved sea-salt particles and the characterization of the sea spray CCN. The broader impacts of this proposal lie in providing research opportunities for undergraduate students, in promoting graduate education and training, and in the application of the results toward constraining the CCN fluxes of natural aerosols against which anthropogenic aerosol effects must be evaluated.