Something in the air

The cold and gloomy stairway with its grit-covered steps was forbidding, but the man in the suit making his way to the roof was undeterred.

A public-health nemesis was on the loose, and Donald J. Dvorin was on the trail of the elusive evidence.

Dvorin is a full-time allergist, but he's also a part-time, volunteer detective. Consulting a homely rooftop machine atop his Center City office building, he's the one who figures out the region's daily pollen counts. And in recent years, they have taken on a fresh importance.

As they do every spring, the region's trees are dispersing their microscopic pollen grains to sow the seeds for the next generation. In the process, however, they are tormenting some of Dvorin's patients and perhaps a million other local allergy sufferers.

But something is different these days, say allergy experts, and evidently it's tied to the warming of the last few decades.

These annual reproductive extravaganzas are lasting longer, said Dvorin, who has been the region's official volunteer pollen counter for the National Allergy Bureau for 25 years.

"That's definitely a trend," said Dvorin, founder of the Asthma Center, which has several offices on both sides of the Delaware River.

Historically, the tree season has started in March, picked up steam in April, and ended in June. Now the timetable appears to be moving up, and a secondary tree season is showing up in the fall, he said.

Last year, Dvorin's data detected several September days with significant levels of tree pollen. Those levels were negligible from 1998 through 2000.

The pollen trends track neatly with climate trends during the last two decades - higher temperatures and longer growing seasons.

"We're seeing changes in the wind," said Leonard Bielory, a Rutgers University researcher, allergist, and veteran pollen counter.

Bielory cowrote a study published last month documenting significant increases in the lengths of late-summer ragweed seasons in the United States and Canada, particularly in the higher latitudes.

Though allergies don't rank with, say, cancer and AIDS as a national health problem, seasonal allergies are nothing to sneeze at, Bielory said.

The numbers of the allergic are swelling, constituting up to 30 percent of all adults and 40 percent of children, according to the American Academy of Allergy, Asthma, and Immunology. Bielory said the increases coincided with the mysterious and alarming bump in asthma diagnoses. Pollen allergies can exacerbate chronic respiratory problems.

Like Dvorin, Bielory began counting pollen 25 years ago and has noticed a lengthening of the seasons. Eventually he secured a federal grant to track the changes.

Pollen-counting is labor-intensive, and the National Allergy Bureau has 85 stations across the country, including Dvorin's, all operated by volunteers.

On workdays before he sees patients in his office at Broad and Race Streets, Dvorin leaves his ordered universe and climbs three flights of stairs to the rooftop trap that captures the grains. Even the bigger ones measure a mere 50 microns, or 0.002 inches, small enough to make a flyspeck seem like a manhole cover.

As small as they are, even tinier fragments of those grains can torture the allergic, said Linda B. Ford, an allergy specialist with a practice in Bellevue, Neb.

During tree-pollen season, most people experience nothing more severe than spring fever. But for the allergic, the immune system views a pollen grain as an adversary. The sneeze is one symptom that the body is fighting back, and on high-pollen days sneezing can be a losing battle.

The trap looks like a small satellite with a large fan blade attached. The pollen is sucked into a coin-slot-size slit and gets attached to a microscope slide coated with an adhesive.

After removing the slide, Dvorin applies droplets of a dye called Calberla's stain and places it under a microscope. The image projected onto the TV monitor resembles a Jackson Pollock painting as images of grains emerge from the squiggly chaos.

From the evidence, Dvorin can infer how many grains - juniper typically rules this time of year - have passed through a parcel of air about the size of a refrigerator in the previous 24 hours. By midmorning, the asthma center posts its daily pollen count.

The 2011 tree season got off to a rip-roaring start with extreme levels - 1,659 grains per 24 hours - reported for the period ending the morning of March 21. That is unusually early for a count that high. But last week it was clear the late-March chill had killed the reproductive mood somewhat, and on Wednesday the count was down to 35, still technically "high."

Certain meteorological conditions are favorable for pollen flight - dry and warm with good breezes.

Under the right circumstances, pollen can fly hundreds of miles from its source. It has been found as far as 400 miles offshore.

Day-to-day pollen production, however, can be wildly variable, and so far no one has been able to predict it reliably, according to pollen experts.

The daily behavior is embedded in another variable: The overall volume of tree pollen can be radically different from year to year, which complicates forecasting and trend-spotting.

For example, based on asthma center data, the volume of tree pollen in 2008 was triple what it was last year.

Why? Spring rain can scrub some of the pollen out of the air, said Estelle Levetin, biology professor at the University of Tulsa, and last spring was extraordinarily wet. In addition, she said, some of the literature suggests individual species have high- and low-pollen years.

Nevertheless, Dvorin said, he does detect an overall increase in tree-pollen volume.

Bielory said the pollen trends almost certainly spoke to changes in the climate.

"People say man's to blame," he said. "I don't know who's to blame, but there is change occurring."