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 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

Introduction

• Historically, measurements used wet chemistrye.g. ozone reaction with I- to form I2

• Wet methods subject to interferences by other gases, generally reported as total oxidants

• Instrumental methods now more common

Roscoe and Clemitshaw, 1997

Gas Reference method

NO2 Chemiluminescence, DOAS

O3 Chemiluminescence, DOAS

CO Nondispersive IR

SO2 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 NO2

O3 + NO NO2* + O2

NO2* NO2 + hν emission from 590 nm to 2800 nm

• Standard reaction for measuring NO

Clyne et al.,1964; Ridley and Grahek, 1990

ChemiluminescenceMeasurement of Nitric Oxide

• Discovery that thunderstorms inject lightning produced NO into upper troposphere

• Affecting O3 levels downstream

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Chemiluminescence Measurement of Ozone

• 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)

• Also possible to use ethene (C2H2)reaction produces excited formaldehyde (HCHO*)

• Measurement of O3 compared to NO

– O3 is found at much larger concentration than NO

– NO (bottle) not convienient for field studies vs method of O3 production (electric discharge in air)

– Smaller reaction vessels are possible for O3 since reagent NO is pure compared to O3

ChemiluminescenceMeasurement 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

• Detection limit: ppt

Boubel et al., 1994

ChemiluminescenceMeasurement 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

• CO reduces NOy to NO over gold catalyst measured via chemiluminescence with O3

Volz-Thomas et al, 2004

ChemiluminescenceRoutine 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

http://www.epa.gov/cludygxb/programs/namslam.html

Routine NOx Monitoring

Decadal cycle

Maxima during rush-hour reflects major source

Spatial

AQEG (2004)

Diurnal cycle

ChemiluminescenceIsoprene 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

Summary and Future Directions

Further ReadingJournal Articles• AEQG (2004) Nitrogen dioxide in the United Kingdom. http://www.defra.gov/environment/airquality/aqeg• 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. 1-108.

• 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.

• Guenther, A.B., and Hills, A.J. (1998) Eddy covariance measurement of isoprene fluxes. Journal of Geophysical Research, Vol. 103 (D11), pp.13145-13152.

• 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. 7291-7297.• Navas, M.J., Jiménez, A.M., and Galán, G. (1997) Air analysis: Determination of nitrogen compounds by chemiluminescence. Atmospheric

Environment, Vol. 31, pp. 3603-3608.

• 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. 307-311.

• Ridley, B. et al. (2004) Florida thunderstorms: A faucet of reactive nitrogen to the upper troposphere. Journal of Geophysical Research, Vol. 109, D17305.

• 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. 1065-1072.

• 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. 6149-6183.