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Ian Livingston

<i>This story has been updated to incorporate Tuesday’s very high tree pollen count.</i>

Peak tree pollen season is here. The normal high point for the year in the Washington area is the third and fourth week of April. And the current season is showing consistently high pollen counts right on schedule.

Washington’s worst allergy days tend to come when tree pollen explodes in early to mid-spring. This year, it actually peaked on March 11, when counts surged to their highest level on record, following an otherwise slow start to the season. The March 11 count of 2,758.47 pollen grains per cubic meter of air has not been tested since although Tuesday’s count around 2,150, the second highest this year, wasn’t too far off.

Such an early spike was unusual, and it may not be surpassed moving forward, but the season so far has been punishing sinuses with a regular barrage of high-pollen days. That’s probably something we should get used to in a warming climate.

Persistently high pollen counts after slow start

<a href="https://pollen.aaaai.org/#/">According to data</a> from the U.S. Army Centralized Allergen Extract Lab in Forest Glen, Md., tree pollen counts first hit moderate levels on March 3. Before that, levels were depressed by unusually chilly February weather. But by the second week of March, counts quickly bounced to high and even very high levels in the second week of the month, climaxing on March 11, due to a sudden spike in temperatures.

Since the first high-pollen day (a count of 80 or higher), on March 9, the D.C. area has piled up at least 28 days of high or very high (a count above 2,000) tree pollen, an unrelenting attack.

Unfortunately for those suffering from sniffles, the mid-March pollen peak wasn’t driven by the trees that typically send counts soaring. Rather, it resulted from early blooming species that erupted from the sudden arrival of warm weather.

“Temperature, sunshine and timing were right to set our cedar/cypress/juniper pollen counts soaring,” Susan Kosisky of the U.S. Army lab wrote in an email, referring to the March 11 spike.

Kosisky, a microbiologist, noted that when temperatures reached the 80s later in March, pollen counts reached <i>only</i> 241.21 among those tree species, indicating they already shed much of their pollen by then. Presently, those early trees are only giving off a tiny fraction of pollen compared to last month.

But now, we’re dealing with oaks, which, along with their cousins pine, mulberry and sycamore, normally drive our peak tree pollen levels each spring.

Oaks are a driver because they make up a huge portion of trees in the area: 47 percent of the annual tree pollen locally can be attributed to oaks, according to Kosisky.

Oaks are currently making up 70 to 75 percent of the daily pollen count. In addition to the yellowish film from the pollen, you might notice their long catkins — small flowering pollen production machines — gathering when they drift off the trees and settle about the landscape.

Because of relatively warm weather this month, tree pollen counts have reached over 500 on the past 10 measurements, mainly due to oaks, including Tuesday’s staggering 2,150. (Counts are not obtained on most weekend days and when it rains.)

There is a little bit of good news in the short term, however.

It could be that the area does not reach 70 degrees for another week. With more temperate conditions settling in, it may be that the D.C. area sees steady rates on the lower end of high pollen, rather than the explosive shorter spurts of very high pollen often seen in late April.

“If the cooler temperatures in the 60s or low 70s prevail we will indeed see a more steady release of pollen from day to day over a period of time at lower levels,” Kosisky wrote.

Even if we don’t see another super high-end peak to close out April, the continuation of elevated levels that began in March is unlikely to please pollen sufferers.

Relief from tree pollen gradually occurs in May, but then grass pollen picks up where tree pollen leaves off through May and into June.

This year’s extended tree pollen season seems to back up data suggesting climate change is playing a role in its longevity.

“Advances in pollen season start date and increases in spring pollen integrals strongly support a phenological seasonal shift of pollen loads to earlier in the year,” concluded<a href="https://www.pnas.org/content/pnas/118/7/e2013284118.full.pdf"> a 2020 study</a> published in the Proceedings of the National Academy of Sciences.

Another key finding in the study? “Long-term increases in pollen season length and annual pollen integrals indicate that exposure times to allergenic pollen as well as amount of pollen have increased significantly for North America in recent decades.”

Given that even small changes in a season can have dramatic effects on public health, this will be an issue of importance for years to come.

Ian Livingston is a forecaster/photographer and information lead for the Capital Weather Gang. By day, Ian is a defense and national security researcher at a D.C. think tank.

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