A new cavity enhanced trace gas absorption detector for CARIBIC

A new cavity enhanced trace gas absorption detector for CARIBIC

‌‌‌‌Researchers:              Laser Spectroscopy Group/CRAC/ ERI/ UCC

Funding Body:            Science Foundation Ireland (SFI)  / Karlsruhe Institute of Technology (KIT)

Period:                        36 months; March 2015 – March 2018

 

 

Project Description:

Apart from oceanic and terrestrial factors, our present understanding of the Earth's climate and its dynamics depends heavily on the observation of relevant atmospheric parameters. Therefore all models that aim at the description of a system as complex and variable as the Earth's atmosphere, heavily rely on monitoring technologies on a variety of platforms (ranging from ground-based sensors to balloons, aircrafts, and satellite-borne instrumentation). The need for monitoring the Earth's atmosphere and the importance of the observational aspects in climate research are presently shifting the focus from quantitative atmospheric science to that of cutting-edge technology and engineering.

In this context, the Laser Spectroscopy Group and ERI, were awarded an SFI grant in the Strategic Partnership Programme in November 2014, to develop a trace gas detector within the framework of the European collaborative large scale IAGOS-CARIBIC project (www.caribic-atmospheric.com). The aim of CARIBIC (=Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container, Fig. 1) is to study the distribution of greenhouse gases, trace species, reactive radicals and aerosol in the upper troposphere/lower stratosphere (UTLS) globally, at altitudes typically between 10 and 12 km. For that purpose an airfreight container with 15 different automated instruments from 8 European research partners is utilized on board a commercial Lufthansa airbus 340-600 (Fig. 2) to monitor over 100 atmospheric trace species in the UTLS. The instrumentation in the CARIBIC container to be supplemented by a new cavity ring-down device for monitoring nitrogen oxides,  jointly developed by researchers from Cork (Ireland), Boulder (USA) and Karlsruhe (Germany). The compact and light-weight instrument (Fig. 3) is designed to monitor NO3, N2O5, NO2 and O3. The detection is based on 4 high-finesse optical cavities (cavity length ~44 cm). Two cavities are operated at 662 nm (maximum absorption of NO3), the other two at 405 nm (maximum absorption of NO2). The inlet to one of the (662)-cavities is heated in order to thermally decompose N2O5 entirely to provide the sum of NO3 and N2O5, with N2O5 provided by difference to a direct NO3 measurement in a separate, unheated channel. One of the (405)-cavities is flushed continuously with NO in order to measure O3 concentrations via quantitative conversion to NO2. The air sampled underneath the cargo bay of the aircraft is distributed inside the instrument through a dedicated inlet system distributing the flow over all four cavities. Flow control, data collection, analysis, and zeroing procedures are fully automated and controlled by dedicated electronics and software within the device. The device is being certified by Lufthansa technique in Spring 2017 and is expected to fly in Autumn/Winter 2017.

The chemistry of NO3 and N2O5 is important to the regulation of both tropospheric and stratospheric ozone. In situ detection of NO3 and N2O5 in the upper troposphere lower stratosphere (UTLS) represents a new scientific direction as the only previous measurements of these species in this region of the atmosphere has been via remote sensing techniques. Because both the sources and the sinks for NO3 and N2O5 are potentially stratified spatially, their mixing ratios, and their influence on nitrogen oxide and ozone transport and loss at night can show large variability as a function of altitude. Aircraft-based measurements of heterogeneous N2O5 uptake in the lower troposphere have uncovered a surprising degree of variability in the uptake coefficient [1], but there are no corresponding high altitude measurements.

 

References:

[1] S.S. Brown, T.B. Ryerson, A.G. Wollny, C.A. Brock, R. Peltier, A.P. Sullivan, R.J. Weber, J.S. Holloway, W.P. Dubé, M. Trainer, J.F. Meagher, F.C. Fehsenfeld, A. R. Ravishankara, Variability in nocturnal nitrogen oxide processing and its role in regional air quality, Science, 311 (2006) 67-70.

 

Fig. 1: The CARIBIC Container on board a Lufthansa Airbus A340-600.

 

 

Fig. 2: Converted Lufthansa Airbus A340-600 of the CARIBIC project with sample gas inlet nozzle underneath the cargo bay.

 

Fig. 3: Close up photograph of the “CAvity Ring-Down Instrument for the detection of Nitrogen Oxides” (CARDINO) in the CARIBIC container.

 

 

Environmental Research Institute

University College Cork, Lee Road, Cork

Top