From Wildfires to Widespread Smoke: Design Strategies for Managing Air Quality in a Changing World
The New Normal: Wildfires and Air-Quality Warnings
The growing impact of climate change has led to an alarming increase in wildfire size and severity, resulting in a 27-fold* increase in smoke exposure across the United States (U.S.) over the past decade. In 2021, extreme heat domes and widespread wildfires on the West Coast and Canada caused significant disruption, with smoke pollution spreading across the continent. For many, this was a stark realization of wildfires' vast risks and far-reaching effects. Remarkably, while 2021 set records for the disruption caused by wildfire smoke, 2023 surpassed it, with smoke exposure increasing by two-thirds*.
- 2/3
- more people were exposed to wildfire smoke in 2023 than in 2021
The air quality in the U.S. has been steadily improving, largely due to the Clean Air Act of 1963 and its subsequent amendments. This legislation effectively regulated point-source pollution – such as emissions from energy production, transportation, and industrial activities – significantly reducing exposure to Particle Matter (PM) 2.5.
PM 2.5 consists of tiny particles that penetrate the lungs and enter the bloodstream, leading to various health issues, including asthma, heart attacks, and neurological disorders. However, these environmental and public health advancements are now undermined by the seasonal threat of wildfire smoke pollution. This emerging hazard affects millions as it spreads across state and international borders.
The PM 2.5 threat is a new concern that requires a thoughtful and strategic response. As we face increased risk from wildfire smoke, ozone, urban heat island effects, and prolonged allergy seasons due to climate change, a robust approach to managing air pollution has become essential. This is particularly critical in areas supporting vulnerable populations or conducting vital research, where maintaining safe and healthy conditions is paramount.
Outdoor air pollution and extended pollen seasons are major pathways for particulate matter exposure.
Urban heat islands in densely built environments can cause airflow stagnation, leading to the entrapment of airborne pollutants.
Odor Threshold VS. Health Standard
The Environment Protection Agency (EPA) has established two criteria for acceptable indoor air quality based on the type of chemicals in the airstream. Odor perception involves four major dimensions: detectability, intensity, character, and hedonic tone. Odor detectability, or threshold, refers to the minimum odor concentration that can be detected by 10-50% of the population. For most contaminants, the health standard is set considerably higher than the odor threshold.
It is important to note that even if an odor is detectable, the concentration may still be within safe health limits. This distinction can be challenging to convey to building owners, operators, and occupants, as there is a common misconception that the presence of an odor indicates a health risk.
Why is Filtering Smoke So Difficult?
Environmental contamination during a wildfire event consists of airborne particles that vary in size, with the particle size depending on the proximity to the fire. During such events, the concentration of airborne particulate matter increases significantly. Larger particles can typically be removed from a building’s ventilation system using standard filtration. However, these filters can quickly become clogged and overloaded, reducing the system’s effectiveness. To protect more expensive and higher-rated downstream filters, bag-type filters in air handler frames are advisable. Bag filters, with their large surface area for particle capture, perform well under high particulate loads and maintain lower pressure drops even after considerable exposure. Implementing a maintenance regimen that includes regular filter replacement is crucial to combat poor indoor air quality.
Except for more critical spaces like healthcare facilities, Minimum Efficiency Reporting Value (MERV) 13 filters are generally recommended as the baseline for cleaning normal outdoor air conditions. Regularly replacing MERV 13 filters can help improve indoor air quality during periods of poor outdoor air conditions. However, according to the British Colombia Centre for Disease Control, “It is unlikely that MERV 13 or lower efficiency filters would provide effective protection from wildfire smoke.” Upgrading filters with higher MERV ratings or Higher Efficiency Particulate Air (HEPA) filters can enhance particle campus effectiveness. Nevertheless, this also increases static pressure requirements. When considering filters with higher MERV ratings, it is essential to account for fan power limits to avoid exceeding system capabilities.
- 90%
- wildfire smoke particles are PM 2.5
The smallest smoke particles can travel great distances, often responsible for the odor and haze we experience even when a fire is hundreds of miles away. These fine particles present a unique challenge for standard air filtration systems. While HEPA filters are 99.97% effective at removing particles that are 0.3 microns or larger, smoke particles can be as small as 0.01 microns. Such ultrafine particles can even pass through HEPA filters, making them difficult to capture and remove from the air.
Air Filtration Improvements
Traditional MERV-rated filters cannot capture small, odor-bearing particles or neutralize odorous gasses. To address this, filter technologies like activated carbon can greatly improve air quality. Activated carbon filters absorb smoke particles and odorous compounds via a porous carbon material bonded to polyester fibers, thereby reducing the smell of smoke. However, the lifespan of activated carbon filters is uncertain, and they are generally more expensive than standard MERV 13 filters. The amount of impregnated carbon is a key factor in determining the filter’s effective lifespan and odor-removal capacity.
- 56,580
- wildfires in 2023
A load shedding strategy prioritizes critical areas, reducing stress on the system and maintaining essential operations.
Advanced Air Filtration Technology
Photocatalytic oxidation filters (PCO) filters operate differently from capture-type filters. Instead of trapping particles, PCO filters use a photocatalytic reaction to neutralize various air contaminates, such as volatile organic compounds (VOCs) that cannot be captured by standard MERV and HEPA filters. PCOs expose titanium dioxide or oxide-coated surfaces to ultraviolet (UV) light, generating hydroxyl radicals and super-oxide ions. These highly reactive electrons interact with airborne pollutants and pathogens, breaking them into harmless and odor-free by-products.
Although PCO filters cannot react with all particulate types, they are effective against the particulates and gases commonly found in wildfire smoke. PCO filters convert these contaminants into carbon dioxide and water vapor. Unlike capture filters, PCO filters do not store or accumulate particles, meaning they do not require periodic filter replacement. These systems can be retrofitted into existing air handlers, but require a thorough field investigation to assess the retrofit impact and overall feasibility.
Tiered resilience levels with clean air zones in critical areas of the building enhance energy efficiency and longevity.
In addition to exploring filtration options for controlling wildfire particulates and odors, various design and operational strategies can enhance resilience to wildfire smoke and mitigate its impact.
Building Design Strategies
- Tiered resiliency: Prioritize critical activities, programs, and supporting systems to enhance resiliency.
- Control infiltration: Ensure a tight building envelope and effective pressurization to minimize smoke infiltration.
- Upgrade air filtration: Consider higher levels of air filtration based on the criticality of the activities served.
- Evaluate humidification needs: Assess and adjust humidification levels as needed.
Operational Strategies
- Create clear air zones: Segment and isolate building areas to establish designated clean air zones.
- Monitor air quality: Regularly check outdoor air quality using reliable websites.
- Maintain filter inventory: Keep a filter and pre-filter stock for timely replacements.
- Optimize ventilation: Reduce outside air volumes where possible to minimize smoke intake.
- Prevent smoke ingress: Implement measures to limit the entry of smoke and unconditioned outside air.
*Burke et al., 2023. The contribution of wildfire to PM 2.5 trends in the USA