Breakout Summary Report

The Aerosol Processes Working Group (APWG) seeks to facilitate communication and collaboration on aerosol processes between ARM, ARM campaign leads, and ASR principal investigators to optimize utilization of measurements and increase the impact of the program as a whole.

The APWG session started with a short introduction of the APWG by the current working group co-chairs Markus Petters & Nicole Riemer, followed by a 30 min speed networking session. Attendees were given the prompt to discuss the question for 2 min (1 min each): What is the most exciting/pressing aerosol related science question that you are working on within the ARM/ASR program? After each encounter, attendees rotated to find a new partner. The goal of this activity was to spark conversations among participants who might not typically interact, encourage cross-disciplinary dialogue, and help build new connections across the APWG community. Each participant was paired with ~10 other participants during the event.

Next, brief presentations by the ARM Aerosol Translator (John Shilling) and the Aerosol Measurement Science Group (Timothy Onash) invited the APWG members to participate in the larger programmatic efforts to coordinate aerosol measurements.

The remainder of the session was dedicated to open discussion organized around five topic areas. Participants first engaged in small group conversations, then reconvened to share key takeaways with the full group through oral reports and contributions to a shared Google document The discussion prompts were:

1. How could we, as the aerosol working group or individual PIs, quantify the impact of aerosol measurement and modeling activities in relation to the overall mission to improve the predictive ability of regional and global earth system models?

2. How could the working group foster better collaborations amongst members of the working group? And how could the working groups interact to address intersecting science questions.

3. What critical aerosol measurement or modeling capabilities are missing or could be improved to increase the scientific impact of ARM campaigns?

4. Any extra products or value added products that we should encourage ARM/ASR to work on/implement?

5. What aerosol products are you currently using?

How could we, as the aerosol working group or individual PIs, quantify the impact of aerosol measurement and modeling activities in relation to the overall mission to improve the predictive ability of regional and global earth system models?

Important points raised by the participants included:

(1) Development of a framework on how to communicate the value (financial or social) to policy makers.

● Focus on US models and how models can create opportunity in prediction of hazards events (water cycle, drinking water, food production)

● More closely couple observations with modeling such that observations support models

● Focus on the quantification of different earth system processes to extreme events that have more visible impact rather than reducing uncertainty from models.

(2) Direct improvement of predictive ability remains challenging for observationalists.

● Measurements should be used to either justify or refute assumptions made in the model.

● Observationalists should be connected to the model without having to run the model

● Create a common venue (workshop) to better connect modelers and observationalists

to help tune models to represent the aerosol properties well.

● Develop new measurement strategies that address capabilities missing from existing aerosol observing systems.

● Using aerosol observations to guide AI/ML with respect to modeling?

(3) If the goal truly is predictive capacity of models, the current structure of large investment in field campaigns with modeling may not be the best strategy.

● Improve the structure of campaigns, focusing on fewer and larger campaigns.

● The focus of these campaigns tends to be measurements first, modeling later. New structure may be needed - or an alternative set of desired outcomes beyond predictive capacity?

● Since most of the aerosol measurements are conducted at the surface, how do we incorporate the horizontal and vertical heterogeneity into the prediction of the aerosol impacts?

● How do we define improved predictive ability in models? Future predictions or historical performance or both? Improving process representation in models doesn't always result in improved predictive ability.

How could the working group foster better collaborations amongst members of the working group? And how could the working groups interact to address intersecting science questions?

Important points raised by the participants are summarized as follows:

The working groups largely function at the annual meeting. Newsletters are a helpful push on specific topics, but they do not add much to generating new science. It might be helpful if there were specific topics set out by the WG that people could join in for online discussion, sharing of research, etc. Setting some specific goals might be helpful. There was a consensus that in-person meetings are key to success but online meetings might be used to augment. DOE-hosted webinars by PIs of funded projects could help. Adding virtual meetings during the year to discuss goals and collaborate might help. Funding travel to connect modelers and experimentalists might help. Also, setting up other collaborative communication channels such as Slack might help to connect scientists over a distance. The annual inperson meeting could be used to discuss the outcomes from these meetups and collaborations. Collaborations across the working groups could furthermore be fostered by including featured presentations from other WGs within the APWG breakout session and vice versa.

What critical aerosol measurement or modeling capabilities are missing or could be improved to increase the scientific impact of ARM campaigns?

Important points raised by the participants are summarized as follows:

There was a broad consensus calling for more vertical structure measurements (e.g. TBS deployments) to characterize the vertical profile of the aerosol size distribution, CCN, and CN, scattering and absorption profiles, and/or size-resolved chemical composition. In-situ measurements for aerosol absorption (not just filter based) , aerosol trace gas and VOC measurements, regularly collected aerosol filters, improved characterization of particles larger than 500 nm would be helpful and additional intercomparison plots were suggested to be needed. Bridging the gap between local (measurements)-toregional (model) scale is important. Multi-site ARM measurements are great, but sites with many instruments are very useful as well, especially for any ML applications, which need a lot of contextual data.

Any extra products or value added products that we should encourage ARM/ASR to work on/implement?

Important points raised by the participants are summarized as follows:

Linking of surface (e.g., microphysics) and columnar (optical) aerosol properties for model validation. Optical sizing instruments are needed to access portions of the aerosol size distribution. More attention to how to make these more robust would be helpful. Calibration results of the aerosol systems could be made more broadly available e.g., the transmission efficiency of aerosols through the AOS, as well as calibrations of SMPS, CPC, and ACSM. An interactive portal that lays out why different periods of observations were of interest for different groups. This could save some time between groups in figuring out what happened during that period. Several participants brought up the opportunity for using LLMs to improve data search and utilization.

What aerosol products are you currently using?

Participants listed aerosol size distribution data (and welcomed the merged VAP), nephelometer data, INP data that are now being collected routinely or for campaigns, ACSM data, and CCN data.

Stronger integration of observations and models is essential to increase scientific impact. Participants emphasized the need for closer coupling between aerosol measurements and modeling activities—both to test model assumptions and to guide future model development. Improved communication channels, co-designed campaigns, and shared frameworks were identified as key enablers.

New strategies are needed to define and demonstrate the value of aerosol science. A call was made for the development of frameworks to better communicate the societal and predictive value of aerosol research—especially to policy-makers—by linking aerosol processes to visible and impactful outcomes such as extreme weather, and water availability.

Enhancing year-round collaboration can help sustain momentum beyond the annual meeting. Attendees expressed interest in virtual meetings, targeted online discussions, and collaborative platforms (e.g., Slack) to facilitate ongoing interaction. These tools could help build community, foster cross-WG collaboration, and support junior researchers throughout the year.

Expanded vertical profiling and underutilized aerosol measurements offer major opportunities. There was broad agreement that improving vertical resolution (e.g., via TBS or UAVs) and expanding key in-situ capabilities—especially for aerosol absorption, trace gases, and supermicron particles—would significantly enhance the scientific value of ARM data for both modeling and ML applications.

User-friendly tools and metadata products can maximize the accessibility and impact of ARM data. Suggestions included an interactive portal to explain campaign periods and objectives, broader access to calibration data, and leveraging emerging technologies (e.g., LLMs) to support more efficient data discovery and utilization.

N/A

N/A

N/A

The discussion as summarized above generated several ideas that we’d like to try out between now and the next PI meeting (see Action Items).

Pilot a year-round engagement plan. Launch a set of recurring virtual touchpoints—such as quarterly webinars featuring PI updates or focused discussion hours on emerging science topics —to maintain momentum and expand involvement between in-person meetings. A Slack channel could support this community-building effort.

Develop a working group initiative to articulate the societal relevance of aerosol science. Outline how APWG research contributes to broader Earth system goals. This could involve a white paper or policyaimed brief that connects aerosol processes to high-impact outcomes and quantifies benefits where possible.