Fall Air Quality Updates for Forsyth County

What’s Up, Forsyth? In this blog post, we explain how the air pollution and airborne pollen levels are changing seasonally. We also compare Forsyth County’s air quality and pollen season in 2024 with 2023 and share tips for reducing air pollution exposure this winter.

How is our air quality changing this time of year?

Ground-level ozone season (the period of time when we monitor and forecast for ozone) lasts from March 1st to October 31st. This is because sunlight and heat are needed for it to form. Between November 1st and February 28th/29th, ozone concentrations are much lower since our days are shorter and colder, and it is not necessary, nor required by the Environmental Protection Agency (EPA), to monitor for ozone in North Carolina during this period.

Particulate matter (PM) concentrations can be high any time of year, therefore, we monitor PM and provide the air quality forecast for fine particulate matter (PM2.5) year-round. PM levels are generally higher in winter months for several reasons:

  1. Increased use of heating systems (fireplaces, furnaces, wood-burning stoves and systems that rely on burning fossil fuels).
  2. Cold air holds less moisture than warm air, so there is less precipitation to wash out pollutants.
  3. PM levels could increase due to temperature inversions. With less heat and sunlight, temperatures can become colder near the surface than the air above (which is the opposite of how it is most of the time). The warm air acts like a lid on top of the denser, colder air at the surface, trapping all types of pollution (PM, carbon monoxide, nitrogen dioxide, sulfur dioxide, volatile organic compounds, etc.) at ground level where we breathe. Air quality can become worse overnight or early in the morning until the sun warms the surface and mixes the air again.

Figure 1. National Weather Service diagram showing how temperature inversions can trap air pollution closer to the Earth’s surface, making the air we breathe more polluted.

Like with ozone monitoring, our pollen program is seasonal. During late fall and winter, there is almost no airborne pollen as most vegetation becomes dormant. We reported airborne pollen concentrations for the last time in 2024 on November 1st.

How is Forsyth County’s outdoor air quality this year compared with last year?

Forsyth County remains (since 2015) in attainment of the national ambient air quality standards (NAAQS) set by EPA through the Clean Air Act. This year, we had fewer days when the air quality was recorded as a code orange or greater (4 code orange days to date in 2024 vs. 6 code orange days and 1 code red day in 2023). We had more days with poor air quality last year because of Canadian wildfire smoke that was transported all the way to North Carolina during an anomalous weather pattern in the summer of 2023.

With that being said, we have had the lowest percentage of code green (good) air quality days in 2024 compared with the last five years (see Figure 2). So far, we have had ~57.5% code green days vs. ~58.5% this time last year. In the years before that, we had closer to 70%, and in 2020, when fewer people were driving their vehicles, we had nearly 80% code green days, which was the best air quality we had experienced since we began our ambient air monitoring program.

Figure 2. Percentage of Code Green Days from 2019-2024 in the Piedmont Triad on November 15, 2024. So far, we have had the fewest number of code green days in 2024.

The fact that we have had more code yellow days and fewer code green days does not mean that our air quality is getting worse. Due to the Environmental Protection Agency (EPA)’s recent rule change regarding the annual PM2.5 standard, there is now a narrower range for what is considered good air quality (0.0-9.0 µg/m3), and since the threshold from a code yellow to code orange did not change, there is now a wider range of what is considered moderate (code yellow) air quality (9.1-35.4 µg/m3). For more information on the new standard and how this affects us in North Carolina, visit www.deq.nc.gov/pm2.5updates.

How did this year’s pollen season compare with last year?

Overall, the 2024 pollen season was similar to 2023. From year to year, we observe slight variations in the timing of peaks of pollen types and/or species, and it takes years of data to discern new trends. Here are some changes based on pollen types compared with last year:

Trees- In the spring, we observed higher concentrations of tree pollen in April (when oak pollen reaches its peak). In the late summer/fall, we noticed that lacebark elm peaked earlier this year than last year (end of August vs. mid-late September).

Figure 3. 7-day Rolling Average for tree pollen using the Pollen Rating Scale (PRS). Data from 2024 and 2023 are shown individually, whereas data from 1997-2022 are averaged together. We adopted the PRS from the American Academy of Allergy, Asthma and Immunology (AAAAI). Learn more at https://pollen.aaaai.org/#/pages/reading-the-levels.

Grasses- This year, we observed higher concentrations of grasses earlier in the season (March) but lower concentrations at the end of season (October).


Figure 4. 7-day Rolling Average for grass pollen using the Pollen Rating Scale (PRS). Data from 2024 and 2023 are shown individually, whereas data from 1997-2022 are averaged together. We adopted the PRS from the American Academy of Allergy, Asthma and Immunology (AAAAI). Learn more at https://pollen.aaaai.org/#/pages/reading-the-levels.

Weeds- Weed pollen levels were lower than last year overall, including a lower spike in ragweed pollen that we typically see in September. We also observed the first weed pollen grains of the season a couple of weeks later than in 2023.

Figure 5. 7-day Rolling Average for weed pollen using the Pollen Rating Scale (PRS). Data from 2024 and 2023 are shown individually, whereas data from 1997-2022 are averaged together. We adopted the PRS from the American Academy of Allergy, Asthma and Immunology (AAAAI). Learn more at https://pollen.aaaai.org/#/pages/reading-the-levels.

What can Forsyth and Piedmont Triad residents do to protect their health during the winter?

1)     Continue to check air quality conditions and forecasts:

Ozone season will begin March 1, 2025, but particulate matter can be high any time of year. Check your air quality daily at forsyth.cc/eap, airnow.gov, or the AirNow app! Alternatively, you can sign up for email or text alerts at enviroflash.info. Read EPA’s Air Quality Guide for Particle Pollution to know how to modify your activities based on the Air Quality Index color codes.

We will begin counting pollen again in early February. For now, airborne tree, grass, and weed pollen should be absent or extremely low, so those with pollen allergies can breathe easy. Don’t forget to start checking pollen counts and forecasts around the first week of February!

2)   Try these pollution reduction tips:

  • Avoid unnecessary engine idling: Minimize idling in the morning since most modern vehicles only need to warm up for about 30 seconds before driving off gently. If there’s frost on your windshield, use an ice scraper or a melting solution to speed up the process.
  • Practice trip chaining: Combine your errands as much as possible since your engine pollutes less when it stays warm in between short strips. You will also drive less distance overall and save time by trip chaining.
  • Avoid burning your leaves/yard waste: Instead, you can leave them—which has several benefits for you and our environment, compost them, or use yard waste pick up options if offered where you live. Never burn trash!
  • Limit fireplace use or wood burners: If you do use them, make sure you have proper filtration and ventilation. You might consider opening the windows so that PM concentrations do not build up in your home. Check out these tips on reducing harmful emissions from wood burning from the American Lung Association. 

      Stay tuned for more blog posts and seasonal updates from our office by following Triad Air Awareness on Facebook, Instagram, and X.

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