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) 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 Used to measure 30 profiles of O3 concentration (balloons) Hilsenrath et al, 1969 Stevens and O’Keefe, 1970

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 Ozone sondes O3 profiles up to 35 km 2KI + O3 + H2O → I2 + O2 + 2KOH I2 is converted back to I- at the cathode 2 types Brewer-Mast cell Electrochemical Concentration Cell (ECC) Tropospheric O3 not well sampled by satellites http://www.fz-juelich.de/icg/icg-ii/josie/ozone_sondes/ecc/ 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 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 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)

Routine NOx Monitoring Heard, 2006 Routine NOx Monitoring Maxima during rush-hour reflects major source Diurnal cycle Source: Heard, 2006 Spatial Decadal cycle

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 (many steps) (CO, HC’s, VOC’s, HCFC’s) (Peroxy radicals) + NO → NO2 + hv → NO + O O + O2 → O3 Very complex!!!

PERCA – Peroxy Radicals by Chemical Amplification 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 OH is recycled back to OH2 to increase concentration of NO2 Cantrell et al., 1993

ROxMAS – ROx Mass Spectrometer 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 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 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. Fahey, D.W., et al. (2001) The detection of large HNO3-containing particles in the winter Arctic stratosphere. Science, Vol. 291, pp. 1026-1031. 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. Guenther, A.B., and Hills, A.J. (1998) Eddy covariance measurement of isoprene fluxes. Journal of Geophysical Research, Vol. 103 (D11), pp.13145-13152. 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. 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. 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. 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. McKendry, I.G. et al. (1998) 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. 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. Ridley, B. et al. (2004) Florida thunderstorms: A faucet of reactive nitrogen to the upper troposphere. Journal of Geophysical Research, Vol. 109, D17305. Schurath, U. et al. (1991) Stevens, R.K., and O’Keefe, A.E. (1970) Modern aspects of air pollution monitoring. Analytical Chemistry, Vol. 42, pp. 143A-148A. Stuhl, F. and Niki, H. (1970) 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.