Field Methods of Monitoring Atmospheric Systems Chemical Methods: Chemiluminescence Copyright © 2008 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 O 3 depletion –Electrochemical sondes (Light-weight instruments) used to measure spatial and temporal distribution of O 3 –Eddy fluxes of O 3 and isoprene from trees –Chemical measurements of radical species HO 2 and RO 2

Introduction Historically, measurements used wet chemistry e.g. ozone reaction with I - to form I 2 Wet methods subject to interferences by other gases, generally reported as total oxidants Instrumental methods now more common Roscoe and Clemitshaw, 1997 GasReference method NO 2 Chemiluminescence, DOAS O3O3 CONondispersive IR SO 2 Fluorescence, DOAS

Chemiluminescence Some reaction products are initially produced in electronically excited states Concentration of emitting species and emitted light intensity is proportional to the concentration of reactant e.g. excess ozone reacts with nitric oxide to form excites NO 2 O 3 + NO  NO 2 * + O 2 NO 2 *  NO 2 + hνemission from 590 nm to 2800 nm Standard reaction for measuring NO Clyne et al.,1964; Ridley and Grahek, 1990

Chemiluminescence Measurement of Nitric Oxide Discovery that thunderstorms inject lightning produced NO into upper troposphere Affecting O 3 levels downstream Ridley et al., 2004

Chemiluminescence Measurement of Ozone Opposite of NO method –Used to make eddy-correlation flux measurements of O 3 –Contributions of chemistry and transport to O 3 budget may be measured (Lenschow et al., 1981) Also possible to use ethene (C 2 H 2 )reaction produces excited formaldehyde (HCHO*) Measurement of O 3 compared to NO –O 3 is found at much larger concentration than NO –NO (bottle) not convienient for field studies vs method of O 3 production (electric discharge in air) –Smaller reaction vessels are possible for O 3 since reagent NO is pure compared to O 3

Chemiluminescence Measurement of NO 2 Total N-oxides (NO x ): Analyzed by thermal or photolytic conversion (more specific) of NO 2 to NO Nitrogen Dioxide (NO 2 ): Difference between NO x – NO Detection limit: ppt Boubel et al., 1994

Chemiluminescence Measurement of Total Reactive N (NO y ) NO, NO 2, NO 3, N 2 O 5, HONO, HNO 3, HO 2 NO 2, ClONO 2, PANs Convert all of the above to NO but not NH 3, N 2 O, HCN CO reduces NOy to NO over gold catalyst measured via chemiluminescence with O 3 Volz-Thomas et al, 2004

Chemiluminescence Routine Measurements Temporal and spatial State and local air monitoring stations (SLAMS) National air monitoring stations (NAMS) Photochemical assessment monitoring stations (PAMS) Mean annual NAAQS 50 ppb

Routine NO x Monitoring Decadal cycle Maxima during rush-hour reflects major source Spatial AQEG (2004) Diurnal cycle

Chemiluminescence Isoprene via O 3 Chemiluminescence Has largest flux of any reactive biogenic HC –Chemiluminescent reaction with O 3 –Diurnal cycle is driven by solar radiation Guenther and Hills, 1998

Summary and Future Directions

Further Reading Journal Articles AEQG (2004) Nitrogen dioxide in the United Kingdom. Boubel, R.W. (1994), Fundamentals of Air Pollution, Academic Press, San Diego, CA 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 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 Guenther, A.B., and Hills, A.J. (1998) Eddy covariance measurement of isoprene fluxes. Journal of Geophysical Research, Vol. 103 (D11), pp Heard (2006) 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 Navas, M.J., Jiménez, A.M., and Galán, G. (1997) Air analysis: Determination of nitrogen compounds by chemiluminescence. Atmospheric Environment, Vol. 31, pp Ridley, B.A. and Grahek, F.E. (1990) A small, low flow, high-sensitivity reaction vessel for NO chemiluminescence detectors. Journal of Atmospheric Technology, Vol. 7, pp Ridley, B. et al. (2004) Florida thunderstorms: A faucet of reactive nitrogen to the upper troposphere. Journal of Geophysical Research, Vol. 109, D Roscoe, H.K. and Clemitshaw, K.C. (1997) Measurement techniques in gas-phase tropospheric chemistry: A selective view of the past, present, and future. Science, Vol. 276, pp Volz-Thomas et al (2004) Measurements of total odd nitrogen (NOy) aboard MOZAIC in-service aircraft: Instrumental design, operation and performance. Atmospheric Chemistry and Physics Discussions, Vol. 4, pp