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Full-Text Articles in Physical Sciences and Mathematics
Development Of An Ambient Pressure Laser-Induced Fluorescence Instrument For Nitrogen Dioxide, Jeremy Parra, Linda Acha George
Development Of An Ambient Pressure Laser-Induced Fluorescence Instrument For Nitrogen Dioxide, Jeremy Parra, Linda Acha George
Environmental Science and Management Faculty Publications and Presentations
Concerns about the health effects of nitrogen dioxide (NO₂) and its role in forming deleterious atmospheric species have made it desirable to have low-cost, sensitive ambient measurements of NO₂. We have developed a continuous-wave laser-diode laser-induced fluorescence (LIF) system for NO₂ that operates at ambient pressure, thereby eliminating the need for an expensive pumping system. The current prototype system has achieved sensitivity several orders of magnitude beyond previous efforts at ambient pressure (limit of detection of 2 ppb, 60 s averaging time). Ambient measurements of NO₂ were made in Portland, Oregon using both the standard NO₂ chemiluminescence method and the …
Measurement Of Free Radicals Oh And Ho₂ In Los Angeles Smog, Linda Acha George, Thomas M. Hard, Robert J. O'Brien
Measurement Of Free Radicals Oh And Ho₂ In Los Angeles Smog, Linda Acha George, Thomas M. Hard, Robert J. O'Brien
Environmental Science and Management Faculty Publications and Presentations
Atmospheric free radicals hydroxyl and hydroperoxyl (OH and HO₂, collectively HOᵪ ) are the catalysts that cause secondary or photochemical air pollution. Chemical mechanisms for oxidant and acid formation, on which expensive air pollution control strategies are based, must accurately predict these radical concentrations. We have used the fluorescence assay with gas expansion (FAGE) technique to carry out the first simultaneous, in situ measurements of these two radicals in highly polluted air during the Los Angeles Free Radical Experiment. A complete suite of ancillary measurements was also made, including speciated hydrocarbons, carbon monoxide, aldehydes, nitric oxide, nitrogen dioxide, and ozone …
Fage Measurements Of Tropospheric Ho With Measurements And Model Of Interferences, Thomas M. Hard, A. A. Mehrabzadeh, C. Y. Chan, Robert J. O'Brien
Fage Measurements Of Tropospheric Ho With Measurements And Model Of Interferences, Thomas M. Hard, A. A. Mehrabzadeh, C. Y. Chan, Robert J. O'Brien
Environmental Science and Management Faculty Publications and Presentations
Ambient HO measurements by low-pressure laser-excited fluorescence with chemical modulation, and supporting ozone and water-vapor data, are presented for periods in May and August 1987. The observed peak daytime ambient HO concentrations in Oregon are in the range (2.5 to 8) times106 molecules cm⁻³ and show small negative offsets due to photochemical interference. Direct measurements of the interference at fixed [O₃] give the dependence on ambient [H₂O] and on the modulating reagent [isobutane]. At ambient [O₃]=30 p.p.b. and 10 torr H₂O, with excitation and detection at a total pressure of 4 torr, the net interference is equal to [HO]=-1.3times10⁶ molecule …
Diurnal Ho₂ Cycles At Clean Air And Urban Sites In The Troposphere, Thomas M. Hard, C. Y. Chan, A. A. Mehrabzadeh, Robert J. O'Brien
Diurnal Ho₂ Cycles At Clean Air And Urban Sites In The Troposphere, Thomas M. Hard, C. Y. Chan, A. A. Mehrabzadeh, Robert J. O'Brien
Environmental Science and Management Faculty Publications and Presentations
HO₂ concentrations have been determined at two Oregon sites for continuous periods of 36 to 48 hours, using fluorescence assay with gas expansion. At the sea level coastal site (45degN 124degW), NNW winds prevailed during daytime, and a point measurement of very low total nonmethane hydrocarbon concentration indicated the presence of remote tropospheric air of oceanic origin. At the urban site, HO₂ was determined during moderately low ozone pollution levels. At both sites, maximum daily [HO₂] was in the range of 1-2times10⁸ cm⁻³ under clear-sky conditions, with an estimated overall uncertainty of 40%.