Direct detection of C 2 H 2 in air and human breath by cw-CRDS Florian Schmidt, Olavi Vaittinen, Markus Metsälä and Lauri Halonen Laboratory of Physical Chemistry, University of Helsinki, Finland

Cavity ring-down spectroscopy (CRDS)

Laser Scan

 int 

Sn



c

 1 0  

Detector

  0    Absorption enhancement due to cavity: 10 3 to 10 5 CRDS independent of laser power fluctuations No calibration needed June 21, 2010 2

Experimental CRDS setup - schematic

Tuning range

: 1520-1575 nm (6350-6575 cm -1 )

Cavity Finesse

: 390 000

Sensitivity

: 7 ×10 -11 cm -1

Acquisition time

: 1 s - 20 min

Detected at ppt level

: C 2 H 2 , NH 3 , HCN

Other detectable species

: CH 4 , N 2 O, CO, CO 2 , H 2 O ECDL = external cavity diode laser OI = optical isolator AOM = acousto-optic modulator MFC = mass flow controller 3 June 21, 2010

Experimental CRDS setup June 21, 2010 4

Motivation to measure acetylene    One of the most common hydrocarbons in the troposphere Mostly anthropogenic sources (fossil- and biofuels, biomass burning) Correlates with other combustions gases and VOCs   Trace pollution and exposure to combustion gases (exhausts, smoking) Baseline of breath C 2 H 2 in the healthy population? Is C 2 H 2 a biomarker for a medical condition (e.g.

Proteus mirabilis

bacterial infection)?

    Not previously detected in ambient air with high time resolution and without pre-concentration.

Not previously quantified in breath GC-MS slow and expensive Not measurable with PTR-MS and SIFT-MS with standard pre-cursors June 21, 2010 5

Spectra from breath and ambient air Air acetylene concentration 0.93 ppbv; Scan time 20 min; Detection limit 120 ppt June 21, 2010 6

System response to C 2 H 2 absorption June 21, 2010 7

Outdoor air – continuous flow

F. M. Schmidt, O. Vaittinen, M. Metsälä, P. Kraus, L. Halonen, Appl. Phys. B (2010) June 21, 2010 8

Day – Night comparison

F. M. Schmidt, O. Vaittinen, M. Metsälä, P. Kraus, L. Halonen, Appl. Phys. B (2010) June 21, 2010 9

Indoor – outdoor air comparison F. M. Schmidt, O. Vaittinen, M. Metsälä, P. Kraus, L. Halonen, Appl. Phys. B (2010) June 21, 2010 10

Breath collection and sample handling  No adsorption/desorption phenomena in the bags, the gas system tubing and the quartz-coated ring-down cavity  Acetylene can be collected and stored in aluminum breath bags (statistical error for 10 bags: 0.4 ppb)  Acetylene concentration stays within 0.4 ppb for 5 days in the bag  No quantitative difference between alveolar/full breath samples and nose/mouth breathing (non-smokers)  Thus: static measurements were possible  Spectrometer temperature: 22 degrees (room temperature)  Sample pressure in the cavity: 0.1 bar June 21, 2010 11

Study - Background level of C 2 H 2 in breath  40 healthy volunteers 22 male, 18 female, 20 to 63 years old, 31 non smokers, 9 smokers  Subjects requested to have stayed at sampling location for 30 min prior to breath collection  One full breath sample collected to a breath bag  At the same time: one ambient air sample collected to a second bag  Samples were analyzed on the same day or at least within 48 hours.

June 21, 2010 12

Results – Breath acetylene minus air acetylene Breath C 2 H 2 baseline = Ambient air C 2 H 2 level Smokers could be identified with a sensitivity and specifity of 100 % June 21, 2010 13

Timer after smoking June 21, 2010 14

Exposure studies  Subject smokes a cigarette or takes a puff  Continuous breathing into CRDS system for up to 30 min  C 2 H 2 decay recorded standing on peak of absorption profile (3 points per second)  For long-term decay: bag samples or shorter intervals of continuous breathing  Fit exponential functions to decay  Simple 3-compartment model (respiratory tract, blood, tissue) June 21, 2010 15

Breath cycles June 21, 2010 16

Acetylene residence times June 21, 2010 17

Summary   CRDS suitable for fast and direct detection of C 2 H 2 in air and breath Mean C 2 H 2 mixing ratio in Helsinki outdoor air of ~1 ppbv  C 2 H 2 correlates with CO, human activity and temperature  Strong fluctuations (up to 60 ppbv on a minute time scale) in urban outdoor air during daytime. Single bag measurements unreliable.

  Breath C 2 H 2 baseline is equal to ambient air C 2 H 2 level Smokers were identified with 100 % sensitivity and specifity  Breath acetylene returns to baseline level around 3 hours after exposure. Urban air pollution could impair smoking status assessment  High-time resolution decay measurements could improve knowledge about residence times of gases and related physiological processes June 21, 2010 18

Acknowledgements June 21, 2010 Dr Olavi Vaittinen Dr Markus Metsälä Peter Kraus Mirva Skyttä Prof Lauri Halonen Academy of Finland 19