Treatment of air pollutants by atmosphericmicroplasma
Kazuo SHIMIZU, Masaki KANAMORI, Masahiro YAMADA
Innovation and Joint Research Center, Shizuoka University, Johoku, Hamamatsu, 432-8561, Japan
E-mail：shimizu@cjr.shizuoka.ac.jp

Abstract
Atmospheric micro plasma is generated in micro gap
electrodes with dielectric barrier. Discharge voltage isonly around 1 kV, though electrode gap is less than
100 um. Through the micro plasma electrode, ozone
and other radicals are generated and removes indoor
air pollutants such as formaldehyde, nitric oxides. Bymaking the micro gap between dielectric barrier
electrodes smaller, a higher ozone concentration could
be obtained.

IntroductionResults(4) BYPRODUCT ANALYSIS(1) ELECTRIC CHARACTERISTICS

FT-IR and 10m gas cell are used to identify thebyproducts after formaldehyde treatment.

BeforeAfter

1kV/div
10us/div

50mA/div
10us/div

N2O

20mA/div

There are many reports on treating hazardous
substances, such as cigarette smoke and VOCs. Mostof these methods require high voltages and has adifficulty against large volume. Therefore, we havecarried out a treatment experiment of formaldehyde
using microplasma reactor, which is more compact,and has low energy consumption.

CO200ns/div

Spike-like currents occur at the steepest slopes ofthe discharge voltage. This is a typical waveform of
dielectric barrier discharge.
The micro plasma reactor can generate atmosphericplasma at about 1 kV, since its discharge gap is very
narrow.

Methods

O3(1) MICRO PLASMA FILTERHCOOH

Pair of metal plates covered with dielectric materials
is used as a dielectric barrier electrode.

(2) DISCHARGE GAPElectric characteristics of micro plasma reactor.

(2) OZONE GENERATION

The discharge gap gives the relation with minimum
sparking voltage and gas pressure (Paschen's law).
Microplasma electrode has an discharge gap between
0-20um.

CH3OH

HCOOH

(5) SMELL ANALYSISThe sample gas was collected and analyzed by a
Fragrance Flavor Analyzer, which has ten different
semiconductor sensors with different sensitivities.
Nine standard gases, each having a different kind ofsmell, are imputed in this device and the analyzed
sample gas is compared with them, outputting thesimilarity against each standard gas.

Ozone and NOx concentration at various discharge
voltages. High concentration of ozone could beobtained, while only a small amount of NOx isproduced.
minimum sparking voltage and discharge gap forvarious gases.
Gas

minimum sparking
voltage (V)minimum gap(um)

Air

330

7.5

Oxygen450

9.2

Nitrogen275

9.9(3) FORMALDEHYDE TREATMENT
The main chemical reaction in the treatment offormaldehyde are the following .

(3) EXPERIMENTAL SETUPConclusions
The following conclusions were obtained by theseries of experiment by using atmosphericmicroplasma.

Dry air, nitrogen, and oxygen are supplied by using anair pump and gas cylinders. Each gas compositions isanalyzed by HPLC, FT-IR, NOx analyzer, ozone monitor,
and Fragrance Flavor Analyzer. Discharge voltage,discharge current, and discharge power are measured
by digital oscilloscope.

The amount of formaldehyde was estimated by theDNPH method using the HPLC.
The initial concentration of formaldehyde was about
3 ppm, which is about 40 times higher than theregulated value in Japan. When the discharge voltage
was higher than 700 V, the concentration dropped
to 0 ppm. To purify 3 ppm of formaldehyde, only 2 W
was required with the microplasma reactor.

①High concentration of ozone can be obtained withlow generation of NOx at low discharge voltage andpower.
②Formaldehyde was purified after microplasma
treatment. Smell of formaldehyde has also changed to
be a similar smell to that of ozone.
③Carbon monoxide and nitrous oxide were found to
be byproducts after the treatment. Also, decrease offormic acid was confirmed.