A.Cuisset, D.Bigourd, G. Mouret, S. Matton, F. Hindle, E. Fertein , R. Bocquet

Laboratory of Physics and Chemistry of the Atmosphere, UMR CNRS 8101,

Université du Littoral Côte d’Opale, Dunkirk

Bigourd & al., Optics Letters, vol. 31 n°6, (August 2006)

The smoke matrix has been shown to be composed of ~ 4000 compounds distributed between the gas and the aerosol phases

R.R Baker, “Smoke chemistry,” in TOBACCO Production, Chemistry and Technology, D.L. Davis, M.T. Nielson, eds. (Blackwell Science, London, 1999), Chapter 12, pp. 398.

• Standard analytical chemistry techniquesStandard analytical chemistry techniques (chromatography, mass spectroscopy…)(chromatography, mass spectroscopy…)

Experimental techniques employed for Experimental techniques employed for the mainstream smoke analysisthe mainstream smoke analysis

These methods generally require:These methods generally require: a sampling method to capture the gas phase a sampling method to capture the gas phase a comparison with a standard of calibrationa comparison with a standard of calibration a detection technique adapted to the system studya detection technique adapted to the system study

• Optical spectroscopy in the infrared regionOptical spectroscopy in the infrared region(tunable diode lasers, quantum cascade lasers…)(tunable diode lasers, quantum cascade lasers…)

Direct in situ measurements in gas phase with a Direct in situ measurements in gas phase with a limited tuning range.limited tuning range.Translation of the measured fractional absorptionTranslation of the measured fractional absorption into absolute concentration not always into absolute concentration not always straightforwardstraightforward

THz linear absorption spectroscopy gives very precise fingerprints of numerous light polar molecules accessing their rotational spectrum.

The translation of the measured fractional absorption into absolute concentration does not require the use of a calibration gas, provided that the spectral parameters are well known.

Molecular information may be obtained in diffusive media ( fog, dust, smoke, flames..) generally opaque at the IR wavelengths.

Possibility of highly selective measurements with weak Doppler contribution of the broadening.

Detection and quantification of molecular species in the cigarette smoke Detection and quantification of molecular species in the cigarette smoke

Advantages of the THz radiationAdvantages of the THz radiation

Broadband analysis of the smoke using THz-Time Domain Spectroscopy Broadband analysis of the smoke using THz-Time Domain Spectroscopy

0 250 500 750 1000 1250 1500

1E-4

1E-3

0,01

Am

plitu

de s

pect

rum

(u.a

)

Frequency (GHz)

0 25 50 75 100-6

-4

-2

0

2

4

6

8

Ave

rag

e c

urr

en

t (n

A)

Time delay (ps)

Broadband radiation from 100 GHz to 1300 GHz

Rapid (few minutes) and simultaneous detection of several rotational lines of hydrogen cyanide, carbon monoxide and water on more one decade of frequency

Low-resolution of the spectrum (2.2 GHz) and strong overlapping between the lines.

Improved spectral resolution can be obtained by CW difference-frequency photomixing Improved spectral resolution can be obtained by CW difference-frequency photomixing

H2OHCNCO

P=950 hPa

V Continuous-wave

optical lasers

THz radiationat the beat note

frequency THz =2 - 1

Photomixer

),t(E 11

),t(E 22

2 1

ttPopt .cos)( 12

t.sin)t(i Thz

)1).(1(2 22222

2

CR

RIP

aThz

aDCThz

Semi-conductor carrier lifetime

Antenna cut off frequency

Mixing of two focused laser beams in a semiconductor-based photomixerMixing of two focused laser beams in a semiconductor-based photomixer

Spectral purity of the source limited by the optical laser sources.Spectral purity of the source limited by the optical laser sources.

Sa:Ti laser 810 nm10 W Verdi

Fiber

4 K Si bolometer

Photomixer+ Silicium Lens

10 W Verdi Sa:Ti laser 810 nm

Absorption cell

polarizer/2

chopper

Lock-in amplifier

The two continuous lasers are monitored by the autoscan systems (Coherent Inc)

8 µm

8 µm

Spiral antennaconnected to the

electrodes

LT-GaAssubstrate

Institut of Electronic, Microelectronic and Nanotechnology Université des Sciences et Technologies, Lille

Collaboration Collaboration with thewith the

Spectral coverage : 100 - 3000 GHz continuouslySpectral coverage : 100 - 3000 GHz continuously Power emitted: 800 nW at 200 GHz, 2 nW at 1 THz and 0.1 nW Power emitted: 800 nW at 200 GHz, 2 nW at 1 THz and 0.1 nW

at 2 THz at 2 THz Sensitivity : Sensitivity : minmin≈≈1010-3-3 cm cm-1-1 at 500 GHz, at 500 GHz, minmin≈4.≈4.1010-5-5 cm cm-1-1 at 1 THz at 1 THz Spectral purity : 5 MHz Spectral purity : 5 MHz

3028,0 3028,1 3028,2 3028,3 3028,4 3028,5 3028,6 3028,7 3028,8

1600

1800

2000

2200

2400

2600

2800

H232S (5

0,5 - 4

4,1)

Am

pli

tud

e,a

.u.

Frequence, GHz

Frequency limit ≈ 3THz

1846.5 1846.6 1846.7 1846.8 1846.9 1847.00.2

0.4

0.6

0.8

1.0

61,6

- 50,5

60,6

- 51,5

Am

plit

ude N

orm

alis

ée

Fréquence (GHz)

23,7 MHz

Frequency resolution ≈

5MHz

Rotational spectrum of hydrogen sulfide HRotational spectrum of hydrogen sulfide H22S (P=0.15 hPa)S (P=0.15 hPa)

T = 294 K, P=20 hPa

Thanks to the large tunability of the laser sources, HCN, CO Thanks to the large tunability of the laser sources, HCN, CO and Hand H22O rotational lines were straightforward assigned O rotational lines were straightforward assigned Spectrum

obtained by a long scan (~ 80 min.)of the CW-

THz spectrometer

Broad and narrow absorptions of HBroad and narrow absorptions of H22O originates from ambient water vapor O originates from ambient water vapor

( P~1013 hPa)( P~1013 hPa) and from the water present in the smoke ( P~20 hPa), respectively.and from the water present in the smoke ( P~20 hPa), respectively.

All the JAll the JJ+1 transitions of HCN with 5<J<26 and CO with 4<J<20 have been clearly J+1 transitions of HCN with 5<J<26 and CO with 4<J<20 have been clearly assigned in the 620 – 2300 GHz frequency range assigned in the 620 – 2300 GHz frequency range

Natural aspiration of the smoke by the evacuated

cell

Thanks to the good spectral purity of the CW-THz source, the transitions line Thanks to the good spectral purity of the CW-THz source, the transitions line shapes allowed to determine the concentrations of the detected species.shapes allowed to determine the concentrations of the detected species.

Lorentzian fit on the J=14 Lorentzian fit on the J=14 -- J=13 transition of HCN J=13 transition of HCN

Pure lorentzian fit :At P = 20 hPa ()collisional >>

()Doppler

Air-broadening coefficient and line position from spectroscopic

database were used.

Results obtained from the intensity measurement of HCN and CO lines:Results obtained from the intensity measurement of HCN and CO lines:

An average value of 210 ppm per cigarette for the HCN concentration with a An average value of 210 ppm per cigarette for the HCN concentration with a standard error of 11 ppm (taking into account the different fits)standard error of 11 ppm (taking into account the different fits)

In the same manner for CO, a concentration of 1.7 % with a standard error of In the same manner for CO, a concentration of 1.7 % with a standard error of 0.3 % per cigarette was measured.0.3 % per cigarette was measured.

The minimum detectable concentrations (at a SNR=1) was estimated to be 9 ppm The minimum detectable concentrations (at a SNR=1) was estimated to be 9 ppm for HCN and 0.1 % for COfor HCN and 0.1 % for CO

HH22CO was detected in the cigarette smoke only at low pressure CO was detected in the cigarette smoke only at low pressure (< 5 hPa).(< 5 hPa).

P=0.7 hPa

P=0.5 hPa

Numerous strong intensity lines of H2CO have been detected and assignedin the 1000 GHz and 1500 GHz

An average concentration of 386 ppm estimated from the profile line shapes is not considered representative of the cigarette smoke for several reasons:

Adsorption onto the cell’s interior surface

Distorsion of the measured line profile

Collaboration with the C. C. M. (Centre Commun de Mesures) Collaboration with the C. C. M. (Centre Commun de Mesures) : F. Cazier

H. NaouiliD. DewaeleStandard analytical chemical methods currently used for each Standard analytical chemical methods currently used for each

compounds detectedcompounds detectedMolecule Chemical analysis

methodMasse per cigarette deduced from the chemical analysis

Masse per cigarette measured by CW-THz

spectroscopy

CO Commercial instrument based on infrared absorption

measurement

109 mg 90 mg

HCN Dosage of the anions CN- by a colorimetric method.

>13.4 µg 1050 µg

H2CO HPLC with UV detection in a DNPH solution

103.7 µg > 16 µg

NH3Dosage of the cations NH4

+

by ion chromatographyusing conductivity detectors

< 0.4 µg < 289 µg

The chemical methods requires a sampling method to capture the gas phase species, the comparison with a standard of

calibration and a detection technique adapted to the molecular system studied.

As in the case of the dosage of CN- anions, other compounds present in the smoke may interfered with the compound targeted.

Detection and quantification of several small polar compounds in a complex and diffusive medium: the mainstream cigarette smoke

Capabilities of trace gas detection at the ppm level for highly polar molecules in an

environment considered as one of the most important indoor air pollutants.

Application of environmental monitoring by CW-THz spectroscopy in a Application of environmental monitoring by CW-THz spectroscopy in a realistic situation where a large number of compounds are present.realistic situation where a large number of compounds are present.

Furthers studies of the cigarette smoke by THz spectroscopy.Furthers studies of the cigarette smoke by THz spectroscopy.

Improvement of the spectrometer sensitivity using a multipass cell in order to detect additional polar components as acetaldehyde, acrolein, formic acid, acetone…

Changing the cigarette combustion process in order to reproduce the true inhalation

of a smoker.

Application of THz spectroscopy in the measurement of breath trace compounds