The GO AQS recently convened two working group sessions focused on establishing limits for particulate matter (PM). These sessions brought together a diverse group of individuals, including toxicologists, building operators, air quality experts, and academics, to discuss and provide feedback on proposed standards for both PM2.5 and submicron particle counts.

Initial Proposals and Feedback on Averaging:

The working group began by addressing the concept of “space adaptability,” aiming to link different average hour concentrations with various indoor spaces to provide more context for users. While the general concept was well-received, some participants suggested changes.

A significant point of discussion revolved around the use of average limits versus target or ceiling limits. While the GO AQS proposal primarily focused on average limits based on existing global standards, some members raised concerns about the potential for high short-term exposures to be masked by longer averaging periods. Members illustrated this with the example of cooking in a kitchen, where a short burst of high particulate matter could still result in an acceptable 1-hour or 8-hour average.

Proposed PM2.5 Limit Tiers:

The GO AQS team presented a two-tiered system for PM2.5 limits: an “ultimate” tier representing a stricter, gold standard, and a “starter” tier with more relaxed limits intended for areas facing socio-economic or technological limitations in achieving higher air quality.

The proposed limits for the ultimate tier included:

• Annual average: 5 µg/m³
• 24-hour average: 15 µg/m³
• 8-hour average: 15 µg/m³ (adapted based on stricter 1-hour and 24-hour values due to a lack of specific 8-hour data)
• 1-hour average: 15 µg/m³ (based on Professor Lydia Maroska’s research)

The starter tier proposed the following limits:

• Annual average: 8 µg/m³
• 24-hour average: 25 µg/m³
• 8-hour average: 25 µg/m³ (closest available value)
• 1-hour average: 25 µg/m³ (closest available value)

Concerns were raised about the differentiation between the starter and ultimate tiers, with one participant suggesting consistent ceiling limits across both. The rationale for the tiered system was explained as a way to facilitate broader adoption of air quality monitoring and improvement, especially in regions facing significant challenges.

The Importance of Ceiling Limits and Real-Time Monitoring:

Some members strongly advocated for the inclusion of separate ceiling limits (short-term exposure limits or STELs), similar to those used in industrial hygiene, to provide immediate warnings about unsafe particulate levels. They argued that relying solely on averages would not adequately address acute exposures.

In response, the GO AQS team emphasized the development of an air quality index (AQI) that would operate in real-time, utilizing data from lower-cost monitors to alert individuals to high concentrations and enable them to take immediate action. The average limits were presented as tools for understanding long-term exposure and benchmarking, while the AQI would address immediate air quality changes. However, the precise relationship between these average limits and the thresholds for the real-time AQI is yet to be fully defined.

Exploring Limits for Submicron Particle Counts:

A significant portion of the discussion focused on the potential inclusion of limits for submicron particles (0.3 and 0.5 microns). The GO AQS team presented data from personal experiments in office and outdoor environments, comparing them to the ISO 14644 standard for cleanrooms. It was explicitly noted that the ISO standard is designed for product yield, not human health.

Several challenges were identified regarding the implementation of submicron particle count limits:

Lack of Health-Based Standards: There is limited scientific consensus and a lack of established health-based standards for these particle sizes in general indoor environments.

Instrumentation Costs and Availability: Reliable instruments for measuring submicron particle counts are currently of a higher-cost (above 300 $) and not commonly integrated into consumer-grade air quality monitors.

Data Scarcity: There is a need for more data and research on typical concentrations and the effectiveness of filtration systems against these smaller particles in various indoor environments.

While acknowledging the potential value of submicron particle counts as indicators of filtration effectiveness, several members, expressed concerns that introducing such limits prematurely, without sufficient data and affordable monitoring technology, could render the GO AQS framework irrelevant or ignored by users. The working group agreed on the need to solicit more data from researchers and the industry before proposing specific limits for these particles.

“Standard” vs. “Guideline”: A Matter of Language and Implementation:

A crucial debate emerged regarding whether the proposed limits should be termed “standards” or “guidelines”. Participants highlighted that “standards” often imply mandatory compliance and enforcement, which might not be feasible or appropriate at this stage. The term “guidelines” was suggested as a more accurate descriptor, reflecting recommendations and aspirational goals rather than strict requirements. The GO AQS team acknowledged this feedback and the importance of clear and accurate terminology.

Considering External Factors and Occupational Settings:

The impact of external air pollution events, such as wildfires, on the ability to meet indoor air quality targets was also discussed. The challenge of balancing the need to bring in outside air for ventilation (to dilute gaseous pollutants) with the potential for increased particulate matter infiltration was highlighted. While acknowledging these challenges, the GO AQS team reiterated the importance of communicating air quality issues to occupants even during external events.

The applicability of GO AQS limits to occupational settings was briefly considered. It was noted that many countries have their own occupational exposure limits, which may differ from general indoor air quality guidelines, and that worker exposure patterns (8 hours/day, 40 hours/week) differ significantly from the continuous exposure of the general public. The GO AQS team indicated a primary focus on general indoor environments rather than specific workplaces.

The Correlational Nature of PM Health Data:

A member also raised an important point about the underlying scientific data linking PM exposure to health impacts, emphasizing that much of it is based on correlations rather than direct causation. He cited examples, such as particulate matter generated during beneficial hospital treatments, to illustrate the complexity of interpreting PM measurements.

Conclusion and Next Steps:

The working group sessions concluded with a summary of the discussions and a call for continued engagement. While no firm decisions were finalized, the following key takeaways emerged:

There is a general agreement on the need to establish guidelines for particulate matter in indoor environments.

The proposed two-tiered system for PM2.5 limits (“ultimate” and “starter”) will be further considered.

The importance of addressing short-term exposures through real-time monitoring and the development of a comprehensive AQI was emphasized.

The inclusion of limits for submicron particle counts requires further research, data collection, and the development of more accessible and reliable measurement technologies. Collaboration with researchers and industry is crucial in this area, as a result, PCN0.3 and PCN0.5 may be postponed for future update of GO AQS version 2.

The terminology used to describe the proposed limits (standards vs. guidelines) needs careful consideration to avoid misinterpretations and ensure appropriate implementation.

The impact of external air pollution events on indoor air quality targets needs to be acknowledged.

The next steps likely involve refining the proposed PM2.5 limits based on the discussions, further developing the concept and thresholds for the real-time AQI, and continuing to explore the feasibility of incorporating submicron particle count metrics as the science and technology evolve. The working group process highlights the complexities and multi-faceted considerations involved in establishing meaningful and practical guidelines for indoor air quality.

• Recording: Particulate Matter WG 1st Session (Failed to record the video, but we have the sound recording if someone needs it.)
• Recording: Particulate Matter WG 2nd Session