Measurement of VOCs for Air Quality Using Widely Tunable Mid-Infrared Laser Source
Combined with Cantilever Enhanced Photoacoustic Detection
Jussi Raittila, CTO, Gasera Ltd.Pittcon 2017, 8. March 2017, 10:05 am
Indoor air quality
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Most people spend approximately 80% to 90% of their time indoors
Indoor air quality has a large impact on health, quality of life and work efficiency
Numerous indoor air impurities are responsible for respiratory diseases , allergies, intoxication and certain types of cancer
Contaminants are caused by e.g. moulds, decomposing floor covering, tobacco smoke, outgassing from furniture
Indoor Air Qu
ality
AIR QUALITY POLLUTANTS
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Contaminant Source Carbonmonoxide(CO) Incomplete combus7on infireplaces, ovens andotherhea7ngappliances, and tobacco
smoking Carbondioxide(CO2) Themetabolismofbuildingoccupantsandpets. Nitrogenoxides(NOx) Sideproductof combus7on. Indoor sources: gasfires, cookingandhea7ngappliances,
smoking Indoor-generatedpar7culatemaFeranddust Carpets, tex7les, food, animal and plant proteins in dust, and occupants (especially in
buildingswithahighdensityofoccupants) Vola/leorganiccompounds(VOCs) Allman-madebuildingmaterialsemitVOCs,especiallywhennewordamaged.
Cleaningproducts. Formaldehyde Buildingmaterials,par/cleboards,householdchemicals,ETS,andcarpetsand
otherhouseholdtex/les. Man-mademineralfibres(MMMF) MMMFareusedininsula7onmaterials,andacous7clinings.Fibresareirritants. Mould (fragments, mouldy material, spores, microbialVOCs)
Mouldgrowthdependsonmoisture:wetstructures,waterleakages,condensa7on,highindoorhumidity
Limonene Freshners,Cleaningproducts,Personalcareproducts InorganicIons Cooking,Smoking Metals Cooking,Smoking,Dust Elementalcarbon(EC),OrganicCarbon(OC) Cooking,Smoking,Dust
PAHs(PolycyclicAroma7cHydrocarbons) Buildingmaterials,Fiberboard,Chipboard,Dust,Cooking,Smoking PCBs(PolychlorinatedBiphenyls) Buildingmaterials,Fiberboard,Chipboard PBDEs(PolybrominatedDiphenylEthers) Plas7cizers,flameretardants
March 2017
TECHNOLOGY & INVENTIONS
PHOTOACOUSTIC SPECTROSCOPY
Photoacoustic effect was discovered in 1880 by Alexander Graham Bell
This theoretical potential has not been reached, since conventional microphones have been used for sensing the pressure pulses
Gaseras novel cantilever sensor technology allows the use of the full potential of the photoacoustic phenomena
Photoacoustic spectroscopy is based on the absorption of light leading to the local warming of the absorbing volume element. The subsequent expansion of the volume element generates a pressure wave proportional to the absorbed energy, which can be detected via a pressure detector.
PHOTOACOUSTIC GAS CELL IR SOURCE
MICROPHONE
IR FILTER
CHOPPER
A typical setup of a conventional PAS system
GAS SAMPLE
GASERAS KEY INVENTIONS Cantilever sensor
Over 100 times greater physical movement can be achieved compared to conventional microphone membrane
Highly linear response
Optical readout system Contactless optical measurement based on laser
interferometry Measures cantilever displacements smaller than picometer
(10-12 m) Extremely wide dynamic measurement range
CONCEPT
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Sensi/vityPatentedcan7leversensorReliabilityPhotoacous7cprincipleVersa/litycanbecombinedwithdifferenttypesoflightsources(NIR-TDL,DFB-QCL,EC-QCL,OPO,BroadbandIRandfilters)
POWERFUL LASER SOURCES FOR VOC DETECTION
March 2017
Two common VOC fingerprint region can be accessed by either an OPO or an EC-QCL
Both OPO and EC-QCL have fairly similar optical characteristics, although the operational principle is completely different
OPO has slightly better output power whereas EC-QCL has a broader tuning range
For a complex VOC matrix, EC-QCL enables more selective detection of multiple gases due to more isolated spectral features
EC-QCL OPO
CASE STUDIES
BTX MEASUREMENT WITH OPO
OPO source from Cobolt AB Sample concentrations about 10
ppm Pulsed OPO (100 mW) + Gasera
PA201 (discrete sampling) Detection limits approx. 10 ppb @
1 second for all compounds Multivariate DL below 1 ppb
PNNL
Photoacoustic
VOC FROM FLOOR COVERING WITH OPO The damage in the floor coverings due to
moisture is a common indoor air problem The emissions of the damaged coverings
lead often to several symptoms to the users of the building.
2-ethyl-1-hexanol (2-EH) is the marker compound for the damage
Present analysis methods are expensive, time-consuming, limited and unreliable
Photoacoustic spectrum between 3398-3458 nm was recorded using a pulsed OPO as a source
The spectral shape of 2-EH can be clearly identified in the measured floor covering sample
Detection limit of the setup for 2-EH is 125 ppt (0.67 g/m3) for 1 min measurement time
UNKNOWN GAS WITH EC-QCL
A case of an impurity in the air of a production plant
A clear impurity was recognized in the measured spectrum
Impurity was identified as methanol (fingerprint)
The methanol concentration was 3 ppm
Detection limit was 0.9 ppb (60 s)
ETHANOL WITH EC-QCL
Detection of EtOH in the presence of water and two other target gases is both selective and sensitive
Detection limit is in the low-ppb level (60 s) for EtOH and two other target gases (VOC and non-VOC)
VOCs WITH EC-QCL
Multi-gas analysis for air quality measurements
Tuning range: 1000 1250 cm-1
Resolution: 1 cm-1
3 minutes response time ppb-level detection limits (1
26 ppb with analysis)
FORMALDEHYDE WITH DFB-QCL
Detection limit (1) is 3 ppb for 1-minute response time and 1 ppb for 10-minute response time.
CONCLUSIONS
Photoacoustic detection combined with widely tunable mid-IR laser sources provides a versatile platform for various air quality applications
High-power EC-QCL in the fingerprint regions enables measurement of many VOCs and also other gases that typically are active in the common fingerprint region
Easy to operate, miniaturization possibilities and infrequent maintenance requirement provides additional benefit
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