J. N. Jun. Pitts

A kilometer pathlength Fourier-transform infrared system for the study of trace pollutants in ambient and synthetic atmospheres.

Abstract A Fourier-transform infrared (FT-i.r.) system operable at pathlengths up to 2 km has been constructed for the detection and measurement of trace contaminants in the ambient atmosphere and in controlled smog formation studies. The long optical path is achieved by the use of an eight-mirror multiple reflection cell with a 22.5-m base path. The design, construction and use of this novel foldedpath optical system are described in detail. In preliminary ambient air measurements at Riverside, California, during the period August–October, 1976, ppb concentrations of formaldehyde, nitric acid, formic acid and ammonia (in addition to O 3 and PAN) were measured in ambient air.

Rate constants for the reaction of OH radicals with COS, CS2 and CH3SCH3 over the temperature range 299–430 K

Abstract Rate constants for the reaction of OH radicals with COS, CS 2 and CH 3 SCH 3 , which are involved in the global sulfur cycle, have been determined over the temperature range 299–430 K using a flash photolysis-resonance fluorescence technique. For COs and CS 2 upper limits at room temperature of k (COS) −15 cm 3 molecule −1 s −1 and k (CS 2 ) −14 cm 3 molecule −1 s −1 were determined, while for CH 3 SCH 3 the Arrhenius expression k (CH 3 SCH 3 ) = 5.47 × 10 −12 exp[(355 ± 300)/ RT ] cm 3 molecule −1 s −1 was obtained with a rate constant at room temperature of (9.8 ± 1.2) × 10 −12 cm 3 molecule −1 s −1 .

Rate constants for the gas phase reactions of O3 with the natural hydrocarbons isoprene and α- and β-pinene

Abstract Rate constants have been determined for the gas phase reaction of ozone with the naturally emitted hydrocarbons isoprene and α-pinene over the temperature range ~ 276 to 324 K, and with β-pinene at 296K. At 296 K the rate constants obtained are ( × 10 17 cm 3 molecule −1 s −1 ): isoprene, 1.17; α-pinene, 8.4 and β-pinene, 2.1. The rate constants for α- and β-pinene are significantly lower than previous literature values, thus increasing the importance of reaction with the OH radical as an atmospheric removal process for these two hydrocarbons.

Kinetics of the reactions of the OH radical with HCHO and CH3CHO over the temperature range 299–426°K

Absolute rate constants for the reactions of the OH radical with HCHO and CH3CHO have been determined over the temperature range 299–426°K by a flash photolysis–resonance fluorescence technique. The Arrhenius expressions obtained are k (HCHO) =1.25×10−11 e−(175±300)/RT cm3 molecule−1⋅sec−1, k (CH3CHO) =6.87×10−12 e(510±300)RT cm3 molecule−1⋅sec−1 with rate constants at room temperature of (9.4±1.0) ×10−12 cm3 molecule−1⋅sec−1 and (1.60±0.16) ×10−11 cm3 molecule−1⋅sec−1 for HCHO and CH3CHO, respectively.

Rate constants for the reaction of the OH radical with CH3SH and CH3NH2 over the temperature range 299–426 °K

Rate constants for reaction of the OH radical with CH3SH and CH3NH2 were determined over the temperature range 299–426 °K by a flash photolysis–resonance fluorescence technique. The Arrhenius expressions obtained were k (CH3SH) =8.89×10−12e(790±300)/RT cm3 molecule−1 sec−1 and k (CH3NH2) =1.02×10−11e(455±300)/RT cm3 molecule−1 sec−1, with rate constants at room temperature of (3.39±0.34) ×10−11 and (2.20±0.22) ×10−11 cm3 molecule−1 sec−1 for CH3SH and CH3NH2, respectively.

Simultaneous absolute measurements of gaseous nitrogen species in urban ambient air by long pathlength infrared and ultraviolet-visible spectroscopy

Abstract Two new long pathlength spectrometers, utilizing 25-m basepath multiple reflection optical systems, were employed for the first time during an intercomparison of measurement methods for atmospheric nitrogenous species held at Claremont, CA, 11–19 September 1985. Measurement of nitrogenous species using these closed optical path systems, as opposed to single pass systems extending several kilometers, permit the resulting in situ absolute spectroscopic data to serve as benchmark values for point monitors employing denuders or filter packs. The FT-IR spectrometer was operated at a total pathlength of 1150 m and spectral resolution of 0.125 cm −1 , with corresponding detection sensitivities of 160 nmolem −3 for HNO 3 and 60 nmole m −3 for NH 3 (4 and 1.5 ppb, respectively). Concurrent measurements of HONO, NO 2 and NO 3 radicals were conducted with the differential optical absorption spectrometer operated at 800 m total pathlength with detection limits of 24, 160 and 0.8 nmole m −3 (0.6, 4 and 0.02 ppb) for HONO, NO 2 , and NO 3 radicals, respectively.

Rate constants for the reactions OH+H2S→H2O+SH and OH+NH3 →H2O+NH2 over the temperature range 297–427 °K

Rate constants for the reactions OH+H2S→H2O+SH (k1) and OH+NH3→H2O+NH2 (k2) were determined over the temperature range 297–427 °K by a flash photolysis–resonance fluorescence technique. The Arrhenius expressions obtained were k1= (5.2±0.5) ×10−12 cm3 molecule−1sec−1, independent of temperature (297–424 °K); k2=2.93×10−12 e−(1710±300)/RT cm3 molecule−1sec−1 with rate constants at 298 °K of k1= (5.25±0.53) ×10−12 cm3 molecule−1sec−1 and k2= (1.64±0.16) ×10−13 cm3 molecule−1sec−1. These rate constants are compared and discussed with literature values.

Rate constants for the reaction of OH radicals with dimethyl ether and vinyl methyl ether over the temperature range 299–427 °K

Absolute rate constants for the reaction of OH radicals with dimethyl ether and vinyl methyl ether have been determined over the temperature range 299–427 °K using a flash photolysis–resonance fluorescence technique. The Arrhenius expressions obtained were k (CH3OCH3) =1.29×10−11 e−(770±300)/RT cm3 molecule−1⋅sec−1, and k (CH2=CHOCH3) =6.10 ×10−12 e(1015±300)/RT cm3 molecule−1⋅sec−1, with rate constants at room temperature of k (CH3OCH3) = (3.50±0.35) ×10−12 cm3 molecule−1⋅sec−1 and k (CH2=CHOCH3) = (3.35±0.34) ×10−11 cm3 molecule−1⋅sec−1.

Rate constants for the reactions of the OH radical with (CH3)2NH, (CH3)3N, and C2H5NH2 over the temperature range 298–426 °K

Rate constants for the reactions of the OH radical with (CH3)2NH, (CH3)3N, and C2H5NH2 have been determined over the temperature range 298–426°K by a flash photolysis–resonance fluorescence technique. The Arrhenius expressions obtained are with rate constants at room temperature of (6.54±0.66) ×10−11, (6.09±0.61) ×10−11, and (2.77±0.28) ×10−11 cm3 molecule−1 sec−1 for (CH3)2NH, (CH3)3N, and C2H5NH2, respectively. Possible mechanisms and atmospheric significance of these reactions are discussed.

Rate constants for the reaction of OH radicals with ethylene over the temperature range 299–425 °K

Absolute rate constants for the reaction of OH radicals with ethylene have been determined, using a flash photolysis–resonance fluorescence technique, over the temperature range 299–425 °K at total pressures of 25–663 torr of argon. The rate constants k2 were observed to be pressure dependent below ∼225 torr total pressure, in agreement with other recent studies. The rate constants were independent of total pressure over the range 225–663 torr of argon, and the Arrhenius expression obtained from data over this pressure range was k2=2.18×10−12 e(770±300)/RT cm3 molecule−1⋅sec−1 with a value at 299 °K of k2= (7.85±0.79) ×10−12 cm3 molecule−1⋅sec−1. This room temperature high pressure rate constant is in good agreement with a recent relative rate determination carried out at atmospheric pressure.