Transcript Field Methods of Monitoring Atmospheric Systems

Field Methods of Monitoring
Atmospheric Systems
Chemical Methods:
Chemiluminescence, Chemical
Amplification, Electrochemistry and
Derivatization
Copyright © 2006 by DBS
Introduction
• Chemical conversion techniques
•
– Chemiluminescence – light production by chemical reaction
– ‘scrubbing’ into solution
– Electrochemical
Measurements
– Routine measurements of urban NOx
– High-altitude aircraft studies of O3 depletion
– Electrochemical sondes (Light-weight instruments) used to
measure spatial and temporal distribution of O3
– Eddy fluxes of O3 and isoprene from trees
– Chemical measurements of radical species HO2 and RO2
O3 (Heterogeneous Chemiluminescence)
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Reaction with dyes
– Excited product transfers energy to
fluorescent dye (liquid or gel)
Early years (luminol and rhodamine-B)
– Regener, 1960; Hodgeson et al, 1970
Stevens and O’Keefe, 1970
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Used to measure 30 profiles of
O3 concentration (balloons)
Hilsenrath et al, 1969
O3 (Heterogeneous Chemiluminescence)
• Since mid-1980s
– Commercial instruments using flowing Eosin-Y on fiber
pad (Ray et al, 1986)
– Coumarin-47 on silica gel (Schurath et al, 1991)
• Summary
– High specificity, low cost, low weight, low power
– Avoid use of compressed hazardous gases (used in
homogeneous techniques)
– High sensitivity and fast response time – most useful
for flux measurements and use in aircraft
O3 via Electrochemistry
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Ozone sondes
O3 profiles up to 35 km
2KI + O3 + H2O → I2 + O2 + 2KOH
I2 is converted back to I- at the cathode
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2 types
– Brewer-Mast cell
– Electrochemical Concentration Cell
(ECC)
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Tropospheric O3 not well sampled by
satellites
Komhyr et al., 1995
Nitrogen Compounds (NO, NO2, NOy)
via Chemiluminescence with O3
• Reactive N compound measurement is
based on the NO + O3 reaction
NO + O3 → NO2* + O2
NO2* → NO2 + hν
Where λ = 600 - 875 nm (Clyne et al.,1964)
Measurement of NO
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O3 (generated in instrument) is
mixed with sample and light
emission measured with
photomultiplier
– Polished gold plated
reaction vessel
– Small size
– Detection limit:
1-2 pptv
Discovery that thunderstorms
inject lightning produced NO
into upper troposphere
Affecting O3 levels downstream
Ridley et al., 2004
Measurement of NO2
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Total N-oxides (NOx): Analyzed by thermal or photolytic conversion
(more specific) of NO2 to NO
Nitrogen Dioxide (NO2): Difference between NOx – NO
Requires scrubber for NH3
Detection limit: 10 ppb (18 μg m-3)
Interferents
convert to NO2
under heat but do
not convert via
photolysis as
strongly
Boubel et al., 1994
Measurement of Total Reactive N (NOy)
• NO, NO2, NO3, N2O5, HONO, HNO3, HO2NO2, ClONO2,
PANs
• Convert all of the above to NO but not NH3, N2O, HCN
• Gold catalyst reduces NOy to NO and CO measured via
chemiluminescence with O3
Forward inlet trace
NOy (HNO3)
particulate spikes
Aft inlet trace:
NOy (HNO3)
Heard, 2006
Maxima during rush-hour
reflects major source
Routine NOx Monitoring
Diurnal cycle
Decadal cycle
Spatial
Ozone via Homogeneous
Chemiluminescence
• Opposite of NO method
– Used to make eddy-correlation flux measurements of O3
– Contributions of chemistry and transport to O3 budget may
be measured (Lenschow et al., 1981)
• O3 compared to NO
– O3 is found at much larger concentration than NO
– NO (bottle) much easier reagent to provide than O3
(discharge)
– Smaller reaction vessels are possible for O3 since reagent
NO is pure compared to O3
Peroxides, HCHO, HONO via Liquid
Techniques
• H2O2 via dissolution and chemiluminescence
– Products of photochemistry (indicator species)
– Reservoirs of odd H radicals
• ‘Scrubbing’ techniques
– Extracted into aqueous solution of luminol and CuSO4
– Detection via PMT
– Detction limit: 1 ppbv (useful for polluted areas)
Kok et al., 1978
• Peroxides via dissolution,
derivatization, and
fluorimetry
• HCHO via dissolution,
derivatization, and
fluorimetry
• HCHO via dissolution,
derivatization, and HPLC
• HONO via liquid techniques
Isoprene via O3 Chemiluminescence
• Has largest flux of any reactive
biogenic HC
– Chemiluminescent reaction with
O3
– Diurnal cycle is driven by solar
radiation
Guenther and Hills, 1998
Peroxy Radicals via Chemical
Amplification
• HO2 and RO2 transfer O to NO to form NO2 wich photolyzes to
liberate an O atom
• O atom combines with O2 molecule to form O3
Trace gases → → RO2 → → CO2 + H2O
(CO, HC’s, VOC’s, HCFC’s)
(Peroxy radicals)
+ NO → NO2 + hv → NO + O
O + O 2 → O3
Very complex!!!
(many steps)
PERCA – Peroxy Radicals by Chemical
Amplification
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Conversion of HO2 to NO2
using reagent NO followed
by detection via luminol
technique
HO2 + NO → OH + NO2
OH + CO → H + CO2
H + O2 + M → HO2 + M
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OH is recycled back to OH2
to increase concentration of
NO2
Cantrell et al., 1993
ROxMAS – ROx Mass Spectrometer
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Using reagent NO and SO2,
followed by CIMS detection of
H2SO4
HO2 + NO → OH + NO2
OH + SO2 + M → HOSO2 + M
HOSO2 + O2→ SO3 + HO2
SO3 + 2H2O → H2SO4 + H2O
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OH is recycled via reaction with
SO2
H2SO4 detected by mass
spectrometry
Advantage: Smaller background
of H2SO4 compared to NO2
Hanke et al., 2002
Summary and Future Directions
• RO2 measurement is ‘lumped’ would like speciation
to define sources
• Likewise with NOy
• Use of LIF for NO2 when NO is a large fraction of NOx
(upper tropsophere)
• Use of in-service aircraft to validate satellite
measurements
Further Reading
Journal Articles
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Clyne, M.A.A., Thrush, B.A., and Wayne, R.P. (1964) Kinetics of the chemiluminescent reaction between nitric oxide and ozone.
Transactions of the Faraday Society, Vol. 60, pp. 359-3770.
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Fahey, D.W., et al. (2001) The detection of large HNO3-containing particles in the winter Arctic stratosphere. Science, Vol. 291,
pp. 1026-1031.
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Fontjin, A., Sabadell, A.J., and Ronco, R.J. (1970) Homogeneous chemiluminescent measurements of nitric oxide with ozone.
Analytical Chemistry, Vol. 42, pp. 575-579.
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Guenther, A.B., and Hills, A.J. (1998) Eddy covariance measurement of isoprene fluxes. Journal of Geophysical Research, Vol.
103 (D11), pp.13145-13152.
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Gusten, H., and Heinrich, G. (1996) On-line measurements of ozone surface fluxes: part I. Methodology and Instrumentation.
Atmospheric Environment, Vol. 30, No. 6, pp. 897-909.
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Hodgeson, J.A., Krost, K.J., O’Keefe, A.E., and Stevens, R.K. (1970) Chemiluminescent measurement of atmospheric ozone.
Analytical Chemistry, Vol. 42, pp. 1795-1802.
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Komhyr, W.D., Branes, R.A., Brothers, G.B., Lathrop, J.A., and Opperman, D.P. (1995) Electrochemical concentration cell
ozonesonde performance evaluation during STOIC 1989. Journal of Geophysical Research, Vol. 100 (D5), pp. 9231-9244.
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Lenschow, D.H., Pearson, R., Jr., and Stankow, B.B. (1981) Estimating the ozone eddy flux and mean concentration. Journal of
Geophysical Research, Vol.86 (C8) pp. 7291-7297.
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McKendry, I.G. et al. (1998)
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Ray, J.D., Stedman, D.H., and Wendel, G.J. (1986) Fast chemiluminescent method for measurement of ambient ozone.
Analytical Chemistry, Vol. 58, pp. 598-600.
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Ridley, B.A., Carroll, M.A., and Greogory, G.L. (1987) Measurements of nitric oxide in the boundary layer and free troposphere
over the Pacific Ocean. Journal of Geophysical Research, Vol. 92 (D2), pp. 2025-2047.
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Ridley, B. et al. (2004) Florida thunderstorms: A faucet of reactive nitrogen to the upper troposphere. Journal of Geophysical
Research, Vol. 109, D17305.
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Schurath, U. et al. (1991)
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Stevens, R.K., and O’Keefe, A.E. (1970) Modern aspects of air pollution monitoring. Analytical Chemistry, Vol. 42, pp. 143A148A.
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Stuhl, F. and Niki, H. (1970)
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WMO (1998)
Books and General Reviews
• Cantrell, C.A. (2003) Observation for chemistry (in situ),
chemiluminescent techniques, in Encyclopedia of Atmospheric
Sciences, Holton, J.R. et al. (eds), Academic Press, Vol. 4, pp.
1454-1460.
• Clemitshaw, K.C. (2004) A review of instrumentation and
measurement techniques for ground-based and airborne field
studies of gas-phase tropospheric chemistry. Critical Reviews in
Environmental Science and Technology, Vol. 34, pp. 1-108.
• Settle, F.A. (ed.) (1997) Handbook of Instrumental techniques
for Analytical Chemistry. Prectice Hall.