Cache Valley Indoor/Outdoor PM Comparison Study
Concerns about student health led Cache County schools (and others throughout
Utah) to institute a policy of canceling recess during high air pollution
inversion events during winter. This policy led to recess and outdoor
activities being canceled some 3 dozen times during the Winter of 2004. Some
questions were raised by parents and others about whether indoor pollution
is any lower than outdoor concentrations during severe inversion episodes.
To answer this, we initiated a study to observe how the particulate
concentrations and composition in school environments varied with the outdoor
levels. We used our
aerosol mass spectrometer
to analyze indoor and outdoor particle concentrations and composition,
alternating indoor and outdoor samples every 10 minutes. This study
was performed collaboratively with
Dr. Randy Martin
, who ran Airmetrics filter samples on both indoor and outdoor air, co-located
with the AMS, as well as at several other schools to make sure the schools
where the AMS sampled were representative.
Sunrise Elementary:
Our indoor/outdoor comparisons study was delayed by ~10 days because of
a turbo pump malfunction as we deployed into the field. During late
January, we setup the AMS to sample at
Sunrise Elementary
in Smithfield, Utah. The AMS stayed in the library of Sunrise for
approximately 2 weeks and sampled indoor and outdoor particle concentrations
and composition. At right, you can see a picture of the AMS sampling
out the window at Sunrise Elementary. You can also see Randy Martin's
indoor Airmetrics sampler just in front of the window.
At Sunrise, we observed that the particle concentrations as detected by
the AMS were consistently 60-80% lower inside, compared to outside. All
chemical constituents detected by the AMS (ammonium, nitrate, sulfate, organic
carbon) were lower concentration indoors. The magnitude decrease in
concentration of ammonium, nitrate, and sulfate inside, relative to outside,
were larger than for the organic carbon, so that if you make pie chart of
the detected chemical composition, the "organic" fraction is larger indoors
than outdoors.
One interesting observation that we made while sampling at Sunrise Elementary
was that the outdoor particle composition detected in Smithfield was different
than when we sampled last year
(January-March 2004)
in Logan. While ammonium nitrate was still the dominant component,
the composition of the organic fraction looked different than what we saw
the year before, specifically, one type of organic particle dominated the
sample, rather than a mixture of several different types of organic signatures
(e.g. diesel smoke, wood-burning, etc.) Last year, the Logan sample
site gave organic fraction that was very complex, with at least four types
of organic particles identified. This raised a important question
not related to the indoor-outdoor study, but critical in understanding the
PM2.5 situation in the Cache Valley: Is the composition
variable throughout the Cache Valley or were the air pollution events of
2005 somehow chemically different than 2004? Because this question
arose during sampling, we had to modify the planned sampling sites. Originally,
we intended to sample at three sites in the Cache County School District:
Sunrise Elementary (Smithfield), Greenville Elementary (N. Logan), and one
of the elementary schools in Wellsville. Now we had to quickly change
course to find a site closer to the downtown Logan site we sampled at in
2004 to see if the composition looked different this year too, while still
conducting the Indoor/Outdoor Comparison.
Logan High School:
We ended up arranging for the AMS to sample at
Logan High School
for several weeks. Logan High is only one block over from the downtown
sampling site that we used during 2004, so it theoretically should be nominally
equivalent sampling location. The AMS spent several weeks inside a science
classroom at LHS. Data acquired at LHS appears similar to Sunrise in
that the particle concentrations inside the classroom were quite a bit lower
than outside most of the time. There were a couple exceptions where
spikes of particle concentration occurred indoors with very different composition
than outside. We are not sure of the source of these particles which
are composed of potassium chloride and organic hydrocarbons and have elevated
concentrations that last for ~ 1 hour each. This is probably indicative
of a temporary combustion source and may be an artifact of sampling in a
science classroom (for instance, if a bunsen burner were lit inside.) We
intend to follow up on this issue with future projects looking at indoor
air in rooms with primary emission sources. For the outdoor composition,
the organic fraction looked similar to the site at Smithfield this year,
and not like what we saw last year in downtown Logan. This makes us
think that there was probably something different in the chemistry behind
the inversion in 2005 than in 2004. This year, due to the dominance
of one particular organic particle type, the overall mass concentration in
Logan shows a strong diurnal pattern where particle mass loadings generally
peaked in the middle of the night.
Analysis of the data from the indoor/outdoor experiment is continuing. We
intend to submit the results in a publication to a relevant journal interested
in the indoor/outdoor air pollution issue. At this point, the major
conclusions from this limited study is that PM concentration inside schools
is generally lower than outside, meaning that the policy to keep young children
inside on high air pollution days does have a health benefit.
We want to thank Steve Zsiray, Associate Superintendent of Cache County
School District and Nancy Bartelt, Principal of Sunrise Elementary for helping
and allowing us to sample at Sunrise Elementary. Thanks also go to
Jack Greene for arranging the sampling site at Logan High School with fairly
short notice.
This page was last updated: June 30, 2005
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