Friedrichs, Gernot

Körtzinger, Arne

Piller,  I.

Sadiek, Ibrahim M.

Wallace, Douglas W.R.

English

OceanRep

                                Evanescent-wave CRDS   [1] C. Fehling, G. Friedrichs, Rev. Sci. Instrum. 81, 053109 (2010) [2] I.  Galli, et al., Phy. Rev. Lett. 104, 110801 (2010) [3] I.  Galli, et al., Phy. Rev. Lett. 107, 270802 (2011) cw-OPO, Aculight Argos™ Model 2400 SF Organohalogen Detection   • Halocarbons play an important role in atmospheric chemistry, e.g. for ozone depletion. • What is the role of the ocean for halocarbon emissions? • What are the sources of halocarbons? • How large is the variability of halocarbons emission? • What controls the distribution of Halocarbons?      Problem: • Organohalogen detection is mainly based on gas chromatography techniques that require considerable calibration effort and is limited to low sampling frequencies.    Sat-CRDS    0 20 40 60 80 10010-610-510-410-310-210-1100 g/c= 0 g/c= 0.5 (low I0) g/c= 0.5 (high I0)"sat"emptyI(t) / I0t / s10-310-210-1100f (tI  c,  g) Deep convection           Atmospheric  Circulation hn, OH  atm.lifetimes from hours to months www.eiu.edu ozonewatch.gsfc.nasa.gov Phytoplankton Macro algae Brominated and iodinated  halocarbons Troposphere Ozone (O3) chemistry OH/HO2, NO/NO2 -cycles Deposition of mercury Involvement in sulfur cycle Aerosol and particle formation Br (I)  15 km Tropical Tropopause Layer (TTL) Ozone (O3) depletion  involving anthropogenic chlorine • Unfortunately, most of the commercially available and field-deployable CRDS instruments are limited to the most abundant trace gases such as, CO2, CH4, and N2O and operated in the near infrared (NIR) spectral range (where absorption cross sections are low). • The project will be concerned with the fundamental spectroscopic and experimental work needed to range the potential of cavity ringdown spectroscopy (CRDS) for environmental monitoring of various halogenated hydrocarbons including bromoform and methyl iodide.  A novel cw-IR laser source (PPLN OPOs ) N2O Spectrum Literature (I. Galli, etal. 2010) Basic principle of CRDS   • For linear absorption:   (0: decay time for the empty cavity, a: absorption coefficient)  Problem: • 0 Needs to be measured separately. • Temporal and spectral variation of 0.   Solution: Sat-CRDS • At high laser power, non-linear absorption can occur due to the saturation phenomena.      (S: the saturation parameter)  • By using saturation CRDS, as illustrated, the empty cavity decay rate and the gas absorption are decoupled and can be retrieved from a single ringdown event. • 14C/C ratios in the present natural abundance samples could be measured with an accuracy of 3.5% in 1 h of averaging. This is merely about 1 order of magnitude worse than the best AMS isotopic ratio uncertainty with the same acquisition time. Radiocarbon-CO2 Detection [2,3] Literature Example of High Sensitivity of Sat-CRDS • The decay curves can be described by: • Use of optical detection techniques such as cavity-ringdown spectroscopy. (adopted from Quack et al.) ( ) exp( ) ( )tI t I f t , ,I ,     a0 000• The actual minimum detectable concentration of 14C16O2 is 43 ppq.  Setup and First Data Example The mode spacing between two longitudinal modes    of ringdown resonator shown on the left. lcv2v(adopted from C. Fehling) • Laborarory studies of atmospheric and marine reactions at quartz-air and quartz-water interfaces. • TIR surface at the base side of the prism mounted in the middle of the cavity induces an exponential decaying evanescent-wave in the space below. • Chemical compounds can adhere at the base side of the prism, absorb energy of the evanescent wave and thus decrease the ringdown time. • NIR-laser source provides radiation in the 1620-1690 nm spectral range (e.g., CH overtone absorption).  Solution: New setup for trace gas sensing application.The infrared laser light source (bluish illuminated devices) offers a wide tunability (l = 1.38 –  1.60 m & 3.2 – 4.6 m),  a narrow spectral bandwidth (n < 60 kHz @ t = 500 s), and high output power (P  1.0 W).  R7 Ocean Interfaces (  (  ( v,I ) v, / Sa  a 0 1ew-cw-NIR-CRDS experiment 

Enhanced CRDS Methods for Trace Gas Detection and Surface Analysis

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