Somerville Transportation Equity Partnership (STEP)

November 20, 2008

Studies on Somerville pollution near highways

The following presentations were given at the recent Conference of the International Society of Environmental Epidemiology and the International Society of Exposure Analysis (ISEE ISEA).

"Spatial and Temporal Distribution of Vehicle Exhaust Emission Gradients Near Highways in Somerville, Massachusetts"

"Traffic-Related Air Pollution in a Densely Populated Urban Area"

"Community Oriented Reuse and Refinement of Available Transportation, Air Quality and Public Health Data to Shape Regional Equity Discussions and Healthier Development Outcomes in Somerville, Massachusetts" (not yet available for download)

The lead authors of the first two are "Ash C" and "Minegishi T" for Christine
Ash and Taeko Minegishi respectively. Taeko did most of the work on the
Environmental Health & Engineering report funded by Federal Realty as part
of the Assembly Square settlement with MVTF. Taeko was assisted by David
MacIntosh of EH&E and Helen Suh of Harvard SPH. Christine based her TUFTs
MS thesis on some of the high resolution near highway measurements MVTF
obtained with the help of the Aerodyne Research mobile lab on the morning of
January 16, 2008. Christine was assisted by John Durant of Tufts and the
Aerodyne scientists.

Taeko's EH&E work shows spatial and temporal variations near I93 for Black
Carbon (BC) and Nitrogen Dioxide (NO2). Both have been used as indicators
of traffic pollution in many environmental and/or health studies. They are
good local indicators of local transportation pollution intensity. Black
carbon is an especially good indicator for diesel vehicle pollution as
diesel vehicles emit a higher fraction of almost pure elemental carbon (EC)
and a smaller fraction of more complex organic carbons (OC) than gasoline
vehicles. NO2 is largely a secondary pollutant formed rapidly in the
atmosphere from NO that is directly emitted from vehicle tailpipes. The
gradients for NO2 are therefore not always as steep as the gradients for
directly emitted NO and for ultrafine particles which evolve more even
rapidly than NO2. Nevertheless Taeko's work shows double the NO2 average
over two weeks at Somerville locations close to I93 compared with locations
several hundred meters further away. The near highway NO2 levels in
Somerville are also about three times the NO2 levels at a background monitor
in Lynn.

Christine's work and the Aerodyne Research data show spatial and temporal
variations as well but on a much shorter time frame. This study is
especially good at portraying the steep early morning gradients for
ultrafine particles from rush hour traffic on I93 and other local highways.
The lack of wind speed, the low temperatures and the low atmospheric
boundary layer condition all contribute to very high particle generation
from hot tailpipe gases emitted. The particle number counts are around
100,000 particles per cubic centimeter of air in Somerville neighborhoods
closest to I93 in the early morning hours of January 16, 2008. Those
particle counts drop off within about 50 to 100 meters upwind and within
several 100 meters downwind. The particle number counts also fall, though
the gradients remain fairly steep, as the morning sun induces higher winds.
The resulting turbulence pushes the atmospheric boundary layer up, producing
a larger air pollution mixing zone and more rapid dilution.

Ultrafine particles themselves evolve quite rapidly, growing in size but
dramatically decreasing in total number count within a few minutes of
formation under most meteorological conditions. (Atmospheric inversions can
be an exception.) Thus people who spend a large portion of their lives
within a few hundred meters of major transportation pollution sources, such
as highways, have uniquely high exposures to ultrafine particles and other
fresh primary emissions. Many health studies from the last decade also show
correspondingly high health impacts for this same near highway population.
This is the primary reason that Somerville and Boston community groups,
along with Tufts Medical School, are now moving ahead with a 5-year $2.5
million NIH funded study called Community Assessment of Freeway Exposure and
Health (CAFEH).