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July 28, 2025
Wildfires are becoming increasingly widespread, especially in North America. On July 24, 2025, the National Interagency Fire Center reported that at least 69 wildfires were burning across the United States. While most documented U.S. wildfires are located in the western United States, the smoke tends to travel eastward because of prevailing wind conditions, exposing millions of Americans to poor air quality.
Similar to heat exposure, wildfire smoke inhalation is a silent killer. Most of the 15,000 wildfire smoke-related deaths attributable to climate change between 2006–2020 were in the West Coast wildfire epicenters. However, wildfire-related deaths can occur hundreds of miles away from the fire source due to drifting smoke. During a wildfire, the intense heat lifts smoke into the atmosphere, where it travels with the wind for hundreds or even thousands of miles. Both the Midwest and the East Coast have already experienced smoke-related reduced visibility and air quality in 2025.
At a chemical and physical level, wildfire smoke is primarily composed of carbon monoxide, carbon dioxide, and particulate matter (also known as soot). Repeated inhalation of either carbon dioxide or carbon monoxide can lead to death by suffocation due to a lack of oxygen in the bloodstream, as oxygen from the air is combusted to fuel the wildfire. However, death by suffocation is only a risk to those in the immediate area of the fire.
The harmful impacts of wildfire smoke are amplified by the particulate matter that is released by the incineration of household objects and building materials. Particulate matter is categorized into fine particles (smaller than 2.5 micrometers) and coarse particles (between 2.5 and 10 micrometers, or μm). One micrometer is around 1.4% of the diameter of a human hair strand. When inhaled, particulates can irritate airways and contaminate human bloodstreams with harmful chemicals, several of which are listed in the graphic below.
According to scientists at the University of Colorado at Boulder, a significant threat is posed by volatile organic compounds (VOCs), such as benzene and formaldehyde, which are emitted by wildfires and travel in smoke plumes. VOCs, which linger in indoor air and on surfaces in homes and other buildings, eventually make their way into the human bloodstream through skin exposure, ingestion, and inhalation. Even short-term exposure to VOCs and other fine particulates is linked to several cancers, accelerated aging, and chronic cardiovascular and respiratory disorders (similar effects apply to household pets and other animals).
When air quality is bad, the usual advice is to go inside. For example, when the interagency AirNow fire and smoke monitoring system indicates that air quality is unhealthy, it states that “everyone should take precautions by reducing outdoor activity; go inside to cleaner air if you have symptoms.” However, indoor air is only truly safe if the particulate matter has been filtered out of it.
Minimum Efficiency Reporting Value, or MERV, is the scale developed by ASHRAE (formerly known as the American Society of Heating, Refrigerating, and Air-Conditioning Engineers) to rate the effectiveness of standard air filtration systems found in the United States. MERV operates on a scale of 1 to 20, though ASHRAE’s internal rating system now stops at MERV 16. The higher the MERV rating of a filter, the better it is at removing contaminants from indoor air. Higher-rated filters are commonly used in hospitals and other medical facilities due to their ability to filter exceptionally tiny particulates (0.3–1.0 μm).
The California Air Resources Board recommends that homeowners secure carbon-based air filters and air purifiers with a MERV rating of at least 13 to successfully filter out harmful particulate matter from wildfire smoke indoors. In American households, MERV 13+ air filters can be bought individually and installed over key vents within homes or apartments. Air purifiers are more straightforward in their use, as they function independently from a building’s existing HVAC system. However, cost is a potential obstacle: a standard whole-home purifier costs $2,610 on average, according to Home Advisor.
All three West Coast states have passed laws encouraging or mandating wildfire smoke filtration in buildings. Two notable examples include Washington State’s HB 1578, enacted in 2023, and the California Green Building Standards Code Section 5.504.53. The former focuses on improving public knowledge of wildfire smoke health impacts, while the latter standardizes the inclusion of MERV 13+ filters in all new residential and non-residential buildings in California to directly mitigate the health impacts of wildfire smoke.
Wildfire mitigation is a hot topic at the federal level. The House Committee on Natural Resources hosted a hearing on wildfire tracking technologies in June 2025, and over 163 bills that mention “wildfire” in their titles have been introduced so far this Congress. While keen Congressional interest in wildfire preparedness and tracking technologies is a start, more can be done to readily provide adequate smoke filtration resources to Americans. Providing federal subsidies to install new MERV 13+ standard heating, ventilation, and air conditioning systems in existing buildings and distributing at-home air purifiers to low-income households could be beneficial, especially considering that low-income individuals are more likely to suffer from wildfire smoke-related health complications.
Improved public knowledge of the dangers of wildfire smoke is also key. A 2022 survey calculated that 63% of American voters were already concerned about the impact of wildfires on their communities. In California alone, likely due to greater exposure to immediate wildfire impacts, 79% of Californians reported in 2019 that they pay close attention to the Air Quality Index during wildfire incidents. This suggests that California’s wildfire air quality communications are highly effective and could be replicated in several states. Perhaps most importantly, West Coast air filtration rules provide a blueprint for protecting Americans’ respiratory health in a warming world.
Author: Jasmine Wynn
Advancing science-based climate solutions
Top-Rated Climate Nonprofit – 4-Star Charity