Detection of volatile organic compounds Detection of volatile organic compounds (��(�� Formaldehyde emissions) in wood Formaldehyde emissions) in wood

based materials by using based materials by using photoacousticphotoacousticinfrared spectroscopyinfrared spectroscopy

byWay Long

Haw-Farn LanYaw-Fuh HuangFanf-Ming Lin

National Pingtung University of Science & Technology, Taiwan, R.O.C.

ContentsContents

• Introduction

• Objectives

• Photoacoustic

• Formaldehyde emissions of wood composite

• Conclusions

Wood is a porous material that has an ability to modulate the moisture and thermal performances. Therefore, wood based materials are often used as constructive and decorative materials in building. However, the effects of volatile organic compounds (VOCs) (eg formaldehyde) from wood based materials have become a great concern of indoor air quality.

IntroductionIntroduction

This study is to investigate the VOCs/formaldehyde by using the photoacoustic analysis to monitor and detect the wood based materials. In order to understand how to prevent the formaldehyde emissions and the related impacts of the concentrations to the indoor environment. Furthermore, to reduce the formaldehyde concentration is using the charcoal adsorbent (activated carbon) in the indoor.

Indoor Environment QualityIndoor Environment Quality

Air Air NoiseNoiseLightingLightingTemperatureTemperatureRelative HumidityRelative HumidityVentilationVentilation(Air exchange)(Air exchange)

Why is indoor air quality a concern today?Why is indoor air quality a concern today?

healthy Indoor Air environments healthy Indoor Air environments

Well-being

High productivity

Lower medical costs

Unhealthy Indoor Air ProblemsUnhealthy Indoor Air ProblemsIllness (Sick symptom)

Injuries

Deaths

Increased medical costs

High exposures indoor environment (WHO1999;US EPA2000)

Typically up to 90% of time spent indoors

Indoor Air Pollutants SourcesIndoor Air Pollutants Sources

Pesticides

Mobile source emissions

powder

Tobacco SmokeCombustion ProductsBiological ContaminantsVolatile Organic CompoundsFormaldehydeSoil gasesPesticidesParticles and Fibers

Indoor pollutions

Outdoor pollutions

ObjectivesObjectives

PhotoacousticAnalysis

Formaldehyde Emissions

vs.Environment

PhotoacousticLASER (light source)Acoustic (receiver)HITRAN

HCHO EmissionsMaterials EmissionsTemperature & RH

•Setup Laser•Calculation•Background test

Theory & Modeling

The aim of this study is to detect formaldehyde(HCHO) emitted inthe wood based materials, so that the technique can improve the indoor air quality.

What’s PhotoacousticThe photoacoustic is a translation of optical energyoptical energy in to mechanical energymechanical energy by the sample (molecule).

Optical energy

Excited

Heating

Acoustic wave

Microphone

When illuminated by light of specific wavelengthspecific wavelength, the molecules become excitedexcited.

The excitation process produces kinetic energykinetic energy or heatheat.(The heating air expansion obtains the pressure variation as acoustic wave)

The detector measures the acoustic wave produced by the sample (molecule).

Gasmicrophone

The The PhotoacousticPhotoacoustic Measurement SetupMeasurement SetupDesiccator

Nd:YAG LaserQ-switchedWavelength: 1064 nm HR 1064nm

Coppermirror

HR 1064nm

PPLN Cell Grating for λs

Gold mirror- controlled by stepping motor

Gefilter

CFIRfilter

MOPAD

MicrophoneLock-in amplifier

Using Laser Condition:Laser frequency: 2790 ~ 2810 cm-1

Laser power: 90mW (in front)Laser light path: 1.0 m (in MOPAD)Room temperature : 22oC+5oCRelative humidity: 60%+ 5%

Power meter

Laser

Optical mirror

Parabolic reflector

Optical mirror

Optical mirror

Parabolic reflector

Microphone

To Lock-in amplifier

MultipassMultipass Acoustically OpenAcoustically Open PhotoacousticPhotoacoustic DetectorDetector (MOPAD)(MOPAD)

0.0E+00

5.0E-05

1.0E-04

1.5E-04

2.0E-04

2.5E-04

2796 2797 2798 2799 2800 2801 2802 2803 2804 2805 2806

cm-1

adso

rptio

n co

effe

icnt

H2O Formaldehyde

Wave number (cm-1)

HITRAN vs. concentration levelsHITRAN vs. concentration levels(H(H22O, HO, H22O with formaldehyde)O with formaldehyde)

Abs

orpt

ion

leve

l

HITRAN (high-resolution transmission molecular absorption database ) --- is a compilation of spectroscopic parameters that use to predict and

simulate the transmission and emission of molecular light.

Formaldehyde TestFormaldehyde Test

Time constant (τ)= 3 min. (200 meas.), laser power ~ 90 mWTotal pressure 1 ATM, ⇒ noise-equivalent sensitivity k=8.1×10-9 cm-1W (Hz)-1/2

The setting wave number for formaldehyde = 2805 cm-1

The lowest level is 0.8 ppbV (10-3 mg/m3)

0.8ppb 1.6ppb 2.4ppb 3.2ppb 4.0ppb 4.8ppb 5.6ppb

0.4

0.6

0.8

1.0

1.2

Phot

oaco

ustic

sig

nal

Formaldehyde concertation

Mean

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

2796 2797 2798 2799 2800 2801 2802 2803 2804 2805 2806

Nitrogen 0.8ppbV

Wave number (cm-1)

Signal

(a.u.)

HCHO level of LVL samples

LVL sampleLoad factor: 3.6 m2/m3

Room temperature : 22oC+5oCRelative humidity: 60%+ 5%

Laminated Laminated venner venner lumber sampleslumber samples

0

5

10

15

20

25

30

35

40

2796 2797 2798 2799 2800 2801 2802 2803 2804 2805 2806

blank2hrs.3hrs.4hrs.

cm-1

Phot

oaco

ustic

sign

al le

vel (

mV

)

671 mg/m3

Formaldehyde level of laminatedFormaldehyde level of laminated venner venner lumber sampleslumber samples

HCHO level of MDF samples

MDF sample (aging over 10 years)Load factor: 6.17 m2/m3

Room temperature : 22oC+5oCRelative humidity: 60%+ 5%

Middle density fiberboard samplesMiddle density fiberboard samples

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2796 2797 2798 2799 2800 2801 2802 2803 2804 2805 2806

blank2hrs.3hrs.4hrs.

cm-1

Phot

oaco

ustic

sign

al le

vel (

mV

)

10.6 mg/m3

Formaldehyde level of MDF samplesFormaldehyde level of MDF samples

Formaldehyde abatement strategiesFormaldehyde abatement strategies

• Low-emission materials • Good ventilation• Humidity & microbial control• Adsorbent materials • Biologically based evaluations

Conclusions

The formaldehyde concentration is increased with photoacoustic signal level increasing.

The measurement lowest level is 0.8 ppbV (10-3 mg/m3)

The method can neglect the moisture influence.

The open test cell can be used as both Lab. and field testing .

The photoacoustic as a dynamic analysis system that can be utilized as VOCs monitor and detection tool.

Thank You

National Pingtung University of Science & Technology