ASHRAE Journal - September 2019 - 8

LETTERS

Changes in IAQ
Caused By Corona
Discharge Air Cleaner
In the December 2018 column "Changes in IAQ Caused
By Corona Discharge Air Cleaner," an in situ test done in
a high school classroom formed the basis for the column.
On reviewing this column, AtmosAir saw several inconsistencies and data presented in such a way that could
bias the reader into an uninformed conclusion. This letter is written to help readers of this column better understand those inconsistencies and better educate the reader.
The column concludes that operation of the corona
discharge air cleaner degraded air quality as there were
increased levels of ozone, aldehydes and ultra-fine particles on days when the air cleaner was in operation.
In the testing described, lemon essence, containing
d-limonene, was evaporated into the subject classroom
during the four separate phases of tests, as described
in the column. It is well known that limonene when
introduced to an environment with any ozone level,
regardless of the source of the ozone, will precipitate
an increase to aldehydes and ultra-fine particles. Many
studies have concluded this (Weschler, C. J., and Shields,
H. C. 1999. "Indoor Ozone/Terpene Reactions as a Source
of Indoor Particles." Atmos. Environ. 33(15):2301-2312).
The column would seem to suggest that the corona discharge air cleaner operation was solely responsible for
these increases, but in fact ambient ozone levels in the
classroom, which cannot be definitively traced to solely
the operation of the air cleaner, were a causal link to any
levels of aldehydes and ultra-fine particles measured.
Also as we well know, ozone is a natural element of
air and can be found in varying levels in both outdoor
and indoor air. Indoor ozone levels have been found
to track to outdoor ozone levels closely (Weschler, C.J.
2001. "Ozone in Indoor Environments: Concentration
and Chemistry." Indoor Air 10(4):269-288). The measured
increases in indoor ozone the test cites had no corresponding outdoor ozone measurements taken, so the
increase in any indoor ozone level cannot be definitively
traced to solely an indoor source or the corona discharge
air cleaner.
Average outdoor ozone levels for the upstate New
York region in 2013 averaged 64 ppb (New York State
Department of Environmental Conservation). The testing
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S E P T E M B E R 2 0 19

TABLE 1 Comparison of contaminant levels.
CONTAMINANT

HIGH MEASURED VALUE

STANDARD

OTHER GUIDELINE

Ozone

34.8 ppb

100 ppb (NIOSH)

50 ppb (CARB)

Formaldehyde

3.74 ppb

16 ppb (NIOSH)

27 ppb (USGBC)

Acetaldehyde

1.71 ppb

200,000 ppb
(OSHA)

25,000 ppb
(ACGIH)

Propionaldehyde

.44 ppb

N/A

20,000 ppb
(ACGIH)

Butyraldehyde

.31 ppb

N/A

Valeraldehyde

.27 ppb

N/A

Hexaldehyde

.37 ppb

N/A

Acetone

8.22 ppb

250,000 ppb
250,000 ppb
(NIOSH)
(ACGIH)
NIOSH = National Institute for Occupational Safety and Health
OSHA = Occupational Safety and Health Administration
USGBC = United States Green Building Council
ACGIH = American Conference of Governmental Industrial
Hygienists
CARB = California Air Resources Board

cites indoor levels ranging from 16.3 ppb to 34.8 ppb.
Since ambient indoor ozone levels can be 10% to 50%
of outdoor levels (Estimating Mortality Risk Reduction and
Economic Benefit From Controlling Ozone Air Pollution. 2008.
The National Academies Press, Washington D.C.), it stands
to reason indoor levels in the ranges measured could be
attributed to the concentrations found outdoors.
The column makes reference to various measured levels of contaminants sampled in the space. However, the
column does not reference what the acceptable exposure limits are for the various compounds measured.
See Table 1 for a comparison.
As you can see the contaminant levels measured
were significantly lower than any published standard
or guideline, and some contaminants were so obscure
that no published permissible exposure limits could be
found. These levels do not show that bad air quality was
found in the tested space in any of the test conditions.
The same can be attributed to the measurements of
ultra-fine particles. Since no baseline was established
nor outdoor levels measured, they cannot be definitively
traced to an indoor source or the corona discharge air
cleaner. Ultra-fine particles lack any indoor standards or
guidelines or permissible exposure limits, so a comparison table cannot be provided.
The column also implies that the findings of this
test were a factor in the New York State Education
Department determining corona discharge air cleaner
systems cannot be used to apply the 403.2 exception,

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ASHRAE Journal - September 2019

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