Cleaner Air

In Washington State, the importance of trees extends far beyond beauty and shade. Urban and community forests serve as a critical public health resource—removing harmful air pollutants, cooling neighborhoods, and protecting residents from respiratory illness. As wildfire smoke, traffic emissions, and climate-driven heat increase across the state, expanding tree canopy is one of Washington’s most effective strategies for protecting public health.

🌿 Trees Clean Washington’s Air—Naturally

Washington communities face rising air-quality challenges, especially in Puget Sound, Southwest Washington, Yakima Valley, and communities near major transportation corridors. Delicate particulate matter (PM2.5), ozone, and nitrogen dioxide (NO₂) are of particular concern due to traffic, wood burning, and increasingly frequent wildfire smoke events.

Urban trees help filter this pollution before it reaches our lungs:

• Leaves and needles capture PM2.5—tiny particles that cause inflammation, asthma attacks, stroke, and heart disease.

• Tree canopies absorb nitrogen dioxide (NO₂), a pollutant strongly linked with childhood asthma in cities like Seattle, Tacoma, and Spokane.

• Trees reduce heat, slowing the formation of harmful ground-level ozone—especially important during summer smoke and heat advisories.

A Washington Department of Health report shows that PM2.5 is responsible for an estimated 1,100 premature deaths each year in Washington, making air pollution one of the state’s most serious environmental health threats. Trees help reduce that burden.

🫁 Proven Health Benefits for Washington Residents

Local research reinforces what national studies have shown: more trees = better respiratory health.

• Washington communities with higher tree canopy coverage have lower asthma ER visit rates, especially among children and seniors.

• Tacoma’s Urban Forest Management Plan notes that increasing tree canopy helps reduce asthma, heat stress, and exposure to pollution in vulnerable neighborhoods.

• A University of Washington research program led by Dr. Kathleen Wolf has produced decades of evidence showing that urban nature reduces stress, improves heart and lung health, and lowers healthcare costs.

This is especially critical for seniors and children—two groups that are most sensitive to pollution and heat.

🔥 Wildfire Smoke Makes Trees More Important Than Ever

Washington’s wildfire seasons have become more prolonged and more severe. Smoke travels hundreds of miles, exposing communities to dangerous PM2.5 concentrations, even in coastal areas. While trees cannot stop wildfire smoke, they help filter particulates and create cleaner “refuge zones” in neighborhoods, reducing long-term exposure.

Tree canopies also cool cities by 2–9°F, reducing both heat-related illness and the chemical reactions that create ozone in hot weather.

⚖️ Washington Laws Recognize Trees as Essential Public Health Infrastructure

Washington State has already laid the legal groundwork for treating trees as critical environmental and health infrastructure:

State Law	Relevance to Trees & Public Health
RCW 76.15 – Urban and Community Forestry Act (2023)	Requires communities to grow and protect urban trees as essential infrastructure for health, environment, and climate resilience.
RCW 36.70A.172 – Growth Management Act (BAS)	Requires cities and counties to use Best Available Science when protecting critical areas—trees are scientifically proven as natural stormwater and pollution filters.
RCW 90.48 – Water Pollution Control Act	Recognizes vegetation (including trees) as natural water filtration systems.

The 2023 Urban & Community Forestry Act strengthened the case for cities and counties to expand tree canopy—not reduce it—because trees are now legally recognized for their public-health value.

🌳 Equity: Planting Trees Where Washington Needs Them Most

The tree canopy is not distributed evenly across Washington. Lower-income neighborhoods, mobile-home communities, and areas with older housing often have fewer trees but higher pollution exposure.

The American Forests Tree Equity Score shows apparent disparities across Washington:

• The lowest canopy often overlaps with the highest asthma rates.

• Communities of color and low-income areas experience higher levels of traffic pollution but have fewer trees to filter it.

Planting and protecting trees in these areas is one of the most direct environmental-justice actions available—and aligns with HEAL Act goals (RCW 70A.02) to reduce health disparities.

💚 A Low-Cost, High-Impact Health Investment

For Washington cities, counties, and HOAs, expanding tree canopy is a high-impact, low-cost investment with massive returns:

• Reduces hospital visits and public-health spending

• Lowers energy bills and cooling costs

• Protects drinking water and reduces stormwater pollution

• Improves mental and physical health for all residents

Every $1 invested in urban forestry returns $4–$12 in benefits, according to the U.S. Forest Service and the i-Tree economic model widely used by Washington cities.

🌱 A Healthier Future for Washington

Urban trees are not optional enhancements—they are lifesaving health infrastructure. As Washington faces rising wildfire smoke, pollution, and climate-related heat, tree protection and canopy expansion are among the most effective strategies available to protect public health.

Growing and preserving tree canopy is a science-backed, cost-effective, and legally supported path to cleaner air and healthier communities.

Planting a tree today means breathing easier tomorrow.

References (APA 7th Edition)

American Forests. (2021). Tree Equity Score: Analysis of urban tree canopy and socio-economic disparities. https://www.americanforests.org/our-programs/tree-equity-score/

Frumkin, H., Bratman, G. N., Breslow, S. J., Cochran, B., Kahn, P. H., Lawler, J. J., Levin, P. S., Tandon, P. S., Varanasi, U., Wolf, K. L., & Wood, S. A. (2017). Nature contact and human health: A research agenda. Environmental Health Perspectives, 125(7), 075001. https://doi.org/10.1289/EHP1663

Nowak, D. J., & Greenfield, E. J. (2018). U.S. urban forest statistics, values, and projections. Journal of Forestry, 116(2), 164–177. https://doi.org/10.1093/jofore/fvx004

Nowak, D. J., Hirabayashi, S., Bodine, A., & Hoehn, R. (2014). Modeled PM2.5 removal by trees in ten U.S. cities and associated health effects. Environmental Pollution, 193, 119–129. https://doi.org/10.1016/j.envpol.2014.05.035

Seattle Urban Forestry Commission. (2021). 2021 Urban Forest Management Plan. City of Seattle. https://www.seattle.gov/trees

Tacoma Urban Forestry Program. (2023). Tacoma Urban Forest Management Plan. City of Tacoma. https://www.cityoftacoma.org/urbanforestry

University of Washington, Nature & Health. (2022). Nature and health research summary: Trees and human well-being. University of Washington College of the Environment. https://natureandhealth.uw.edu

U.S. Department of Agriculture Forest Service. (2016). Benefits of urban trees: Urban forest facts. USDA Forest Service. https://www.fs.usda.gov

Washington State Department of Health. (2020). Health impacts of air pollution in Washington State. Washington State Department of Health. https://doh.wa.gov

Washington State Legislature. (2023). RCW 76.15 Urban and community forestry. https://app.leg.wa.gov/rcw/default.aspx?cite=76.15

Washington State Legislature. (n.d.). RCW 36.70A.172 Best available science to be used. https://app.leg.wa.gov/rcw/default.aspx?cite=36.70A.172

Washington State Legislature. (n.d.). RCW 70A.02 Healthy Environment for All (HEAL) Act. https://app.leg.wa.gov/rcw/default.aspx?cite=70A.02

Washington State Legislature. (n.d.). RCW 90.48 Water pollution control. https://app.leg.wa.gov/rcw/default.aspx?cite=90.48