Breakout Summary Report

ARM/ASR User and PI Meeting

2 - 6 May 2016

Session Title: Aerosol Mixing State
Session Date: 4 May 2016
Session Time: 1:30 PM - 3:30 PM
Number of Attendees: 0
Summary Authors: Nicole Riemer and Matthew West

Breakout Description

The goal of this session was to share recent progress on mixing state-related work amongst modelers and experimentalists, and to discuss current challenges and the way forward.

List of Attendees:
Nicole Riemer (University of Illinois), Matt West (University of Illinois), Bob McGraw (BNL), Leah Williams (Aerodyne), Tim Onasch (Aerodyne), Hailong Wang (PNNL), Kerri Pratt (University of Michigan), John Shilling (PNNL), Rahul Zaveri (PNNL), Mary Gilles (LBNL), Rao Kotamarthi (ANL), Peter McMurry (University of Minnesota), Jim Smith (UC Irvine), Ashley Williams (DOE), Hagen Telg (NOAA/ESRL), Jian Wang (BNL), Andy Freedman (Aerodyne), Qi Zhang (UC Davis), R Subramanian (Carnegie Mellon University), Alex Laskin (PNNL), Jeff Pierce (Colorado State University), Art Sedlacek (BNL), Yan Feng (ANL), Allison Aiken (LANL), Ryan Moffet (University of the Pacific), Matt Alvarado (AER), Manvendra Dubey (LANL/NSF), Claudio Mazzoleni (Michigan Tech University), Larry Kleinman (BNL)

Main Discussion

We started out with a sequence of 5-min presentations to give updates on current activities within the Mixing State Focus Group. During the discussion phase we took stock of the Focus Group progress, and brainstormed ideas of how to move forward.
The list of presentations was as follows:
• Ryan Moffet
• Cari Dutcher
• Mary Gilles
• Gourihar Kulkarni
• Claudio Mazzoleni
• Kerri Pratt
• Joseph Ching
• Laura Fierce
• Hailong Wang
• Rahul Zaveri
• Matthew West
• Art Sedlacek
• Allison Aiken
• Alla Zelenyuk

Key Findings

We had 15 short presentations (~5 min) of individual PIs on mixing-state-related research topics, covering the areas of modeling, field observations, and laboratory experiments.
From those presentations it is very obvious that our state of knowledge about the aerosol mixing state has dramatically improved since the Focus Group has become active. The key advances are:
- We now have a rigorous definition of what “aerosol mixing state” is.
- We have developed model capabilities that can represent mixing state and its evolution from the process level up to the regional scale. This development included rigorous benchmarking and error quantification activities.
- We have developed error quantification techniques to estimate how important mixing state is for CCN activity and aerosol optical properties.
- Field observations from recent campaigns using single-particle measurement techniques have enabled us to characterize existing mixing states in different environments.
- We have developed new measurement techniques to probe different aspects of mixing state.
- Laboratory experiments are enabling us to gain insights into the evolution of mixing state and its impacts.
- Claudio Mazzoleni and Swarup China are guest editors for a special issue in the journal Atmosphere: Morphology and internal Mixing of Atmospheric Particles.

Despite this progress, considering that the ultimate goal is to improve global models, we are still not there yet: The current representation of aerosol mixing state in ACME is still crude and the errors that this introduces for the estimation of aerosol climate impacts are not quantified.

Issues

We framed the discussion with the following three overarching questions, which we need to address to move forward:
(1) Can we compare models from different levels of the model hierarchy to verify the mixing-state representations, mechanisms and impacts? What might this look like? Who is going to do it? What funding do we need to make this happen?
(2) How do we compare mixing-state information between measurement platforms and models?
(3) How do we use measurements (lab and field) and theory to create and validate mechanisms for: (a) mixing- state evolution? (b) mixing-state impacts on IN/CCN/OP?

These are challenging questions at the core of what this focus group should accomplish, and not easy to solve – certainly not within a one-hour breakout group discussion. Nevertheless, the discussion led to several key ideas, which are further detailed below (Needs, Future Plans and Action Items).

Needs

The questions above have one common theme: They require people from different groups and backgrounds to come together. From the discussion emerged the following needs:
- Support for a COmbined Simulation and Instrumentation Experiment (COSINE).
The goal of such a campaign would be to quantify aerosol mixing state in a well-defined environment, and to learn how to intercompare models and different measurement types. There is no single instrument that on its own fully captures “mixing state”. Instead, the full mixing-state information needs to be reconstructed using the information from multiple sources. For example, SP2 measures for particles of a certain size range the masses of BC cores and estimates a coating thickness without knowledge of which individual chemical species form the coating. Single-particle mass spectrometers give the mass spectra of individual particles, and this information is usually aggregated in the clustering of different particle classes. How are these measurements related, and importantly, how can we use them to constrain various types of models? How can we use these measurements synergistically to make the most of the data? We envision this campaign to involve multiple types of instruments, which probe mixing state in various ways, as well as multiple instruments of each type. In addition, multiple models on different levels of the multi-scale model hierarchy will be used to simulate the evolution of mixing state in the aerosol chamber.
- Support for a Simulation INtercomparison Exercise (SINE)
The goal of this endeavor would be to construct one (or more) real-world test cases to evaluate the differences in aerosol climate impacts due to aerosol representation. To accomplish this, we envision setting up simulations for the CARES domain using the same meteorological host model (WRF), the same chemistry mechanism, but different aerosol representations (PartMC, MOSAIC-Mix, the default 8-bin MOSAIC sectional model, MAM4). This will enable us to quantify the impact of aerosol representation on the prediction of CCN concentration and optical properties. This activity will leverage capabilities already developed as part of the Aerosol Testbed.
- Our findings within this Focus Group need to be disseminated to the wider community (survey paper).

Decisions

None

Future Plans

- Further discuss the specifics for the COSINE project
- Follow up with modelers on SINE project

Action Items

- Update of the original focus group white paper
- Assemble writing team for Mixing State survey paper