in a world filled with pollution. Scientists have known for a long time
that particulate matter from sources like diesel shortens life spans by
causing cardiovascular and pulmonary problems. Black carbon—the
tiny particles spewed out in exhaust and other combustion reactions
like fires and cookstoves—are blamed for 2.1 million premature
deaths annually around the world. Scientists have long considered the
lungs as a primary target of pollution. Only recently have they come
to realize the role of the nose as thruway to the brain; the nefarious
extent of the nose-brain connection was only illuminated in 2003,
when researchers in smog-choked Mexico City found weird brain
lesions on stray dogs.
This is unnerving, because particulate pollution is all around us.
It’s very likely a strong factor in why going to the woods makes us
feel better and more cognitively nimble. In the humid microclimates
created by urban forests, leaves soak up particulate pollution. Beneath
the trees, organic carbon in the soil can bind to airborne pollutants,
and it also helps clean surface water in storms. A 2014 study
estimated that trees in the United States remove 17.4 million tons of
air pollution per year, providing 6.8 billion dollars in human health
benefits.
I was curious about how the dynamics were playing out in my
neighborhood. Before I went to Korea, I borrowed a portable
aetholometer from Columbia University’s Lamont-Doherty Earth
Observatory. The device comes from the Greek word meaning “to
blacken with soot.” Velcroed into a twill vest pocket, it sent up a
spindly arm sensor that poked out of my collar like a playful pet
monkey. I wore it around D.C. for three days of my normal routine of
working, walking and driving. Columbia’s Steve Chillrud, codirector
of the Observatory’s Exposure Assessment Facility Core, helped me
collate the data to a real-time GPS tracker in my phone and analyze
the results. Not surprisingly, I measured high readings of 6,000
nanograms per cubic meter while driving on I-495, the Capital