P3-B IN SITU OZONE MEASUREMENTS

Dr. Gerald L. Gregory1, Dr. Bruce E. Anderson1, Dr. Melody A. Owens2,and Mr. Wesley R. Cofer1

The P3-B ozone detector employs the nitric oxide+ozone (NO+O3) chemiluminescent principle. Samples are delivered to the sensor via a J-probe, forward-facing, window-mounted, and Teflon-lined. The NO+O3 chemiluminescent detection principle is a reverse application of the standard technique [Clough and Thrust, 1967; Fontijn et al., 1970] used for detection of oxides of nitrogen and has been used by numerous investigators [Eastman and Stedman, 1977; Pearson and Stedman, 1980; Gregory et al., 1987]. Reaction of O3 in the sample and nitric oxide (NO) supplied via gas cylinder produces an electronically excited state of NO2 which emits (via chemiluminescence) light. The quantity of light detected by PMT circuitry is proportional to O3 in the sample. The NO+O3 chemiluminescent reaction is sufficiently fast (>10 Hz) and has been used in flux studies [Ritter et al., 1992 and 1994). The P3-B instrument is configured for 10 Hz measurements. The instrument is calibrated by gas-phase titration, traceable to NIST nitric oxide gas standards. Corrections for water vapor quenching [Mathews et al., 1977] are applied, post-flight, using inflight data – pressure, temperature, and dew point temperature. Such corrections are at maximum ~10% for near-surface, warm and moist (100% humidity) environments. Above about 3-km altitude corrections are negligible.

Instrument Performance.

Dynamic Range: 0.8 to 1000 ppbv

Response: 10--Hz (based upon sample exchange rate at sea level)

Accuracy: 3% or 2 ppbv

Precision: 1% or 0.8 ppbv @ 2 Hz response; 2 to 3% @ 10-Hz

Sensitivity: Independent of pressure to 15-km altitude

Calibration: Multiple point (5 to 500 ppbv) by NO gas phase titration.

Data Rate: Recorded at 20 Hz (by Project and flux experiments)

Data Reporting: 5-sec average (in the field); 2 Hz & 10 Hz (final archive)

References.

Clough, P.N. and B.A. Thrush, Mechanism of chemiluminescent reaction between nitric oxide and ozone, Trans. Faraday Soc., 63, 915-925, 1967.

Eastman, J.A. and D.H. Stedman, A fast response sensor for ozone eddy-correlation fluxmeasurements, Atmos. Environ., 11, 1209-1211, 1977.

Fontijn, A., A.J. Sabadell, and R.J. Ronco, Homogenous chemiluminescent measurement of nitric oxide with ozone, Anal. Chem., 42, 575-579, 1970.

Gregory, G.L., C.H. Hudgins, J. Ritter, and M. Lawrence, In situ ozone instrumentation for10-Hz measurements: Development and evaluation, Proceedings of Sixth Symposium on

Meteorological Observations and Instrumentation, New Orleans, LA, Jan. 12-16, 1987,pp 136-139.

Mathews, R.D., R.F. Sawyer, and R.W. Schefer, Interferences in chemiluminescent measurement of NO and NO2 emissions from combustion systems, Environ. Sci. Technol., 11,1092-1096, 1977.

Ritter, J. A., J.D. Barrick, G.W. Sachse, G.L. Gregory, M.A. Woerner, C.E. Watson, G.F. Hill,J.E. Collins, Jr., Airborne flux measurements of trace species in an arctic boundary layer, J. Geophys. Res., 97, 16,601-16,626, 1992.

Ritter, J. A., J.D. Barrick, C.E. Watson, G.W. Sachse, G.L. Gregory, B.E. Anderson,M.A. Woerner, and J.E. Collins, Jr., Airborne boundary layer flux measurements of tracespecies over Canadian boreal forest and northen wetland regions, J. Geophys. Res., 99,1671-1686, 1994.

Pearson, R.W. and D.H. Stedman, Instrumentation for fast response ozone measurements fromaircraft, Atmos. Tech., 12, 1980.

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1. NASA Langley Research Center; Atmospheric Sciences Division; Mail Stop 483; Hampton, Virginia23681-0001

2. Hampton University; Department of Physics; Hampton, Virginia 23688