368
M. Pal and M. Pradhan
So far QCL coupled spectrometer has been utilised extensively in varieties of
atmospheric applications including measurements of atmospheric trace species in
urban areas from a complex gas mixture, quantitative estimation of flux and concentrations of the atmospheric gases from aircraft with high sensitivity and fast response.
Moreover, potentials of QCL offer trace species monitoring with high selectivity, nondestructive way by a compact optical spectrometer in real-time. The in-situ monitoring of eddy-covariance flux measurement of CH 4 and N 2 O was accomplished by
a QCL spectrometer near 1270 cm
−1 mid-IR spectral region during 3 months and the
precision of 2.9 and 0.5 ppb Hz
−1/2 were subsequently achieved for CH 4 and N 2 O
concentration measurement respectively [26].
Later, Tuzson et al. demonstrated QCL based infrared absorption spectrometer
(QLAS) for in-situ ambient CH 4 concentration measurement with fast and high
precision near 7.8 μm region [27]. The potential of this QLAS spectrometer, such as
compactness, unattended cryogenic free operation enabled to continuously monitor
the temporal dynamics of atmospheric CH 4 exchange from the ecosystem. However,
the capability of this QLAS instrument for simultaneous eddy covariance flux
measurements of N 2 O and NO 2 with good time-precision was also elaborated in
this study.
Furthermore, the real-time eddy covariance of other important trace molecules in
the atmosphere such as NO [28], N 2 O [29–31], OCS [32], CO 2 isotopes [33] and CH 4
[34] isotopes was monitored in forest area or grassland by utilising different QCL
coupled detection strategies based optical spectrometer in mid-IR spectral range with
high sensitivity and high specificity. Moreover, the importance of atmospheric trace
species monitoring in temporal and spatial variation is very much required to reduce
the adverse effect of human health as a precautionary measure.
In 2002, Weber and his research group introduced a DFB-QCL coupled wavelength modulation spectrometer with multi-pass Heriotte cell near 1921 cm
−1 spectral
region to monitor the NO concentration from vehicle exhaust in few ppb ranges [35].
Later, Wideman et al. incorporated a thermoelectric cooled pulsed QCL operating
at 10 μm in a 100 m optical path length Herriott cell for real-time monitoring C 2 H 4
concentration in vehicle exhaust and high-traffic urban tunnel by probing ν 7 fundamental bands and they successfully achieved noise equivalent sensitivity 30 ppb in
80 s acquisition time [36]. Furthermore, Mitchel et al. demonstrated a widely tunable
(1020–1075 cm
−1 ) QCL based open path system in the mid-IR region to monitor
multiple trace gases such as water vapour, ammonia, ozone and carbon dioxide in the
lower atmosphere of Beijing during Olympic 2008 [37]. In this study, the TE-cooled
pulsed EC-QCL coupled system was to design to operate within path length from 0.1
to 1.0 km and subsequently, fluctuations of target gases up to ppb order were recorded
by this optical system. In order to get proper knowledge about dynamics of ammonia
concentration in the urban area and industrial sector, Gong et al. utilised an EC-QCL
coupled photoacoustic absorption spectrometer (PAS) operating at 10.4 μm to do
the intensive measurement of the NH 3 concentration in Houston during summer and
winter and the system monitored the variation of the mixing ration of NH 3 from
0.1 ppb to 8.7 ppb [38].
M. Pal and M. Pradhan
So far QCL coupled spectrometer has been utilised extensively in varieties of
atmospheric applications including measurements of atmospheric trace species in
urban areas from a complex gas mixture, quantitative estimation of flux and concentrations of the atmospheric gases from aircraft with high sensitivity and fast response.
Moreover, potentials of QCL offer trace species monitoring with high selectivity, nondestructive way by a compact optical spectrometer in real-time. The in-situ monitoring of eddy-covariance flux measurement of CH 4 and N 2 O was accomplished by
a QCL spectrometer near 1270 cm
−1 mid-IR spectral region during 3 months and the
precision of 2.9 and 0.5 ppb Hz
−1/2 were subsequently achieved for CH 4 and N 2 O
concentration measurement respectively [26].
Later, Tuzson et al. demonstrated QCL based infrared absorption spectrometer
(QLAS) for in-situ ambient CH 4 concentration measurement with fast and high
precision near 7.8 μm region [27]. The potential of this QLAS spectrometer, such as
compactness, unattended cryogenic free operation enabled to continuously monitor
the temporal dynamics of atmospheric CH 4 exchange from the ecosystem. However,
the capability of this QLAS instrument for simultaneous eddy covariance flux
measurements of N 2 O and NO 2 with good time-precision was also elaborated in
this study.
Furthermore, the real-time eddy covariance of other important trace molecules in
the atmosphere such as NO [28], N 2 O [29–31], OCS [32], CO 2 isotopes [33] and CH 4
[34] isotopes was monitored in forest area or grassland by utilising different QCL
coupled detection strategies based optical spectrometer in mid-IR spectral range with
high sensitivity and high specificity. Moreover, the importance of atmospheric trace
species monitoring in temporal and spatial variation is very much required to reduce
the adverse effect of human health as a precautionary measure.
In 2002, Weber and his research group introduced a DFB-QCL coupled wavelength modulation spectrometer with multi-pass Heriotte cell near 1921 cm
−1 spectral
region to monitor the NO concentration from vehicle exhaust in few ppb ranges [35].
Later, Wideman et al. incorporated a thermoelectric cooled pulsed QCL operating
at 10 μm in a 100 m optical path length Herriott cell for real-time monitoring C 2 H 4
concentration in vehicle exhaust and high-traffic urban tunnel by probing ν 7 fundamental bands and they successfully achieved noise equivalent sensitivity 30 ppb in
80 s acquisition time [36]. Furthermore, Mitchel et al. demonstrated a widely tunable
(1020–1075 cm
−1 ) QCL based open path system in the mid-IR region to monitor
multiple trace gases such as water vapour, ammonia, ozone and carbon dioxide in the
lower atmosphere of Beijing during Olympic 2008 [37]. In this study, the TE-cooled
pulsed EC-QCL coupled system was to design to operate within path length from 0.1
to 1.0 km and subsequently, fluctuations of target gases up to ppb order were recorded
by this optical system. In order to get proper knowledge about dynamics of ammonia
concentration in the urban area and industrial sector, Gong et al. utilised an EC-QCL
coupled photoacoustic absorption spectrometer (PAS) operating at 10.4 μm to do
the intensive measurement of the NH 3 concentration in Houston during summer and
winter and the system monitored the variation of the mixing ration of NH 3 from
0.1 ppb to 8.7 ppb [38].