Breakout Summary Report
ARM/ASR User and PI Meeting
13 - 17 March 2017
Aerosol Mixing State: Metrics, Modeling, Measurements
15 March 2017
10:30 AM - 12:30 PM
35
Riemer, West
15 March 2017
10:30 AM - 12:30 PM
35
Riemer, West
Breakout Description
The goal of this breakout session was to bring together modelers and experimentalists to work towards integrating the findings from aerosol property measurements in the laboratory and in the field regarding aerosol mixing state with the advances from the modeling community.Main Discussion
The session focused on discussing two questions:1. How can we integrate different experimental techniques to characterize mixing state as fully as possible?
2. How can we use this information to compare to mixing-state-aware models?
We started with an overview that provided background information (presented by Nicole Riemer) and illustrated a key problem in comparing output from a mixing-state-aware model to observed mixing state information, in this case data from the SP2 (presented by Matt West). This was followed by a sequence of 5-minute presentations by several breakout group participants (Hudson, Subramanian, Fraund, Ching, Onasch, Zelenyuk, Dubey), and a full hour of discussion among the entire group.
Key Findings
• No single instrument can characterize the full “mixing state” of an aerosol population, hence the question of how to integrate the different experimental techniques to characterize mixing state as fully as possible.• When discussing mixing state, it is helpful to distinguish between the particle-level properties (chemical composition versus morphology) and the population-level quantities (“how are the chemical species distributed across the population?” versus “what particle morphologies exist in the population?”)
• Progress has been made regarding connecting different tools to paint a more complete and robust picture of aerosol mixing state. The 5-min presentations highlighted the connection of SP2 and microscopy (R. Subramanian), STXM and TEM/EDX (M. Fraund), and using SPLAT and SP2 data for creating initial conditions for particle-resolved modeling (J. Ching).
• Laboratory studies have made important contributions. T. Onasch discussed the absorption enhancement due to coating of BC particles and the associated laboratory measurements at Boston College. The purpose of the BC4 lab campaign was to attempt to produce mixed particles in the chamber that experience the lack of absorption enhancement as seen in the field during CARES. A. Zelenyuk and M. Dubey reported on the SAAS campaign, which was an example of a laboratory campaign that had a comprehensive suite of measurements, focusing on the multi-instrument characterization of soot particle evolution, composition, and properties.
Issues
Progress has been made in developing mixing-state-aware models (MOSAIC-Mix, PartMC) on the one hand, and in measuring different aspects of mixing state with a suite of innovative, sophisticated instruments on the other hand. However, the comparison of model output to measurements is not straightforward: While the model output is based on per-particle mass fractions, SP2 or single-particle mass spectrometers do not directly give mass fractions. So far we do not have rigorous methods of simulating what these instruments “would see”, which is necessary to allow for a quantitative comparison.Needs
As key need we identified the capability to produce “aerosol standards”, i.e., aerosol particles of complex composition that are well characterized. This would not only benefit the aerosol mixing state community, but also the nanoparticle community and the ice nucleation community.Decisions
N/AFuture Plans
• Synthesize results from the SAAS campaign to established the lessons learned and to decide if it would be worthwhile to have a SAAS-2 campaign.• Hold workshop on methods to produce new types of aerosol standards. This would require preparing a white paper that clearly articulates needs. Input should be solicited from both theorists and experimentalists. Prior to the workshop, this white paper might then be circulated among aerosol scientists, not restricted to those in ASR. They should include those from the aerosol materials community who have complementary expertise. The workshop should focus on methods that could be employed to develop aerosol standards that can routinely be used for experimental work.