Air Quality Data Summary for 2023

Fine particles and smog (ozone) are our greatest concerns in Puget Sound. These types of air pollution cause heart attacks, strokes, and even premature death. Air pollution is especially dangerous for children, the elderly, and people with lung or heart diseases.

Since 2015, we have faced unprecedented wildfire smoke—the highest fine particle levels since we started monitoring for them in 1980. In August 2023, we had various wildfires impacting the air quality at our monitoring sites for five days. Due to the vicinity of some of the wildfires in the region, we observed air quality levels reaching unhealthy category in King and Snohomish counties.

The table below shows the air quality health categories over 2023 by county. Overall, most days were in the GOOD air quality category. However, many are MODERATE days and a few days that were UNHEALTHY FOR SENSITIVE GROUPS and UNHEALTHY from wildfire smoke. King County has nearly 40% of the days in the MODERATE category. The EPA health-based air quality index changed in 2024 and we can now expect to see more days in the MODERATE category overall, even though air quality hasn’t worsened compared to last year.

2023 Air Quality, Days by Health Category

Fine particles

Fine particles are tiny, microscopic pieces of pollution which are even smaller than the width of a hair. These can easily enter the deepest part of your lungs and cause breathing and heart problems. In our region, they mainly come from wood smoke from home heating, vehicles, wildfires, and industry.

The graph below shows that all the sites had fine particle levels within the EPA standard (of 35 micrograms per cubic meter) on most days in 2023, except for some days with wildfire smoke, wood smoke impacted days in winter months, and days with July 4th fireworks celebrations. Wildfire smoke impacted the air quality at all sites on 5 days in August (8/20 -8/21/23, 8/25-8/27/23). The graph below shows daily fine particles level for all days in 2023; wildfire excluded days can be viewed by selecting the Wildfire Days Excluded option on the right side of the graph under the section Include Wildfire Days?. Wildfire smoke is considered an “exceptional event” by EPA and these values are excluded from any required regulatory action.

Studies have also shown significant health impacts below the EPA standard as well. Therefore, the Agency has a health goal (of 25 micrograms per cubic meter), which was exceeded up to 2 days in July due to fireworks, 3 days in August due to wildfires and up to 3 days in winter months due to wood smoke from home heating.

Black Carbon

Fine particles that come specifically from diesel exhaust is our greatest concern as they carry the most health risks, but we can’t directly measure them and there is no EPA standard for them. Although not a perfect measurement, we use a “black carbon” monitor to estimate our impacts from diesel pollution. Diesel exhaust represents over 80% of the potential cancer risk from air pollution in the Puget Sound area. Most of the diesel exhaust in the Puget Sound region comes from four transportation sectors: maritime, off-road equipment, on-road vehicles, and rail.

The graph below shows a reducing trend for black carbon since 2002. The levels have remained low in summer and higher in the winter when the air is typically more stagnant. The levels were highest during the wildfire smoke and wood smoke impacted days in the winter months. In more recent years, levels appear to be either flattening or reducing more slowly.

Ozone (also called “smog”)

Unlike fine particles and black carbon, ozone (smog) is created on hot summer days by chemical reactions with different types of air pollution from vehicles, industry, paints, solvents, and gasoline fumes.

In 2023, the ozone levels at the Enumclaw site were lower compared to the previous two years. However, the EPA standard is based on three years of data and the 2021-2023 average (as seen in the graph below) exceeded the standard because of high ozone (and wildfire smoke) years in 2021 and 2022. The ozone levels remained below the standard for rest of the sites. At this time, our region is not designated nonattainment for ozone as EPA isn’t in a standard review year (which is scheduled for every 5 years). They will likely do their review in the next two to three years.

National and local air pollution reduction programs

Nationally, large reductions in diesel exhaust are expected to continue thanks to the newer diesel fuel and truck engine standards that took effect in 2007.  The newer trucks are 50 to 60 times cleaner than the older, dirtier trucks.  In 2011, an international agreement required incoming ships to use the cleanest shipping fuels along US coastlines (called an Emission Control Area) which also reduces diesel exhaust in our area. EPA continues to develop rules to reduce air toxics emitted from large and small industrial sources, which we ensure are implemented by the industries in our four counties through our compliance program.

Washington State recently adopted large sweeping climate actions which will help in reducing the emissions in our four-county region.  These actions include a new low carbon fuel standard, a cap-and-invest program, the WA Clean Energy Transformation Act, a future ban on new internal combustion engines by 2035, and many more.

Our Agency has also been working to further reduce air pollution on a local scale.  With our Diesel Solutions program, we partner with private and government organizations to reduce diesel exhaust.  Through our wood stove replacement program, and continuing to ensure wood heating burn ban compliance, we’ve seen levels of wood smoke come down in our region over the years.  We continue to pursue other opportunities to lower air pollution in the region, including greenhouse gas reductions.

View the detailed 2023 Data Summary.