Richard A. Graham

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.

Temperature dependence of the unimolecular decomposition of pernitric acid and its atmospheric implications

Abstract The decay of pernitric acid (HO 2 NO 2 ) in the presence of excess nitric oxide has been studied in a 5800-liter, Teflon-lined chamber over the temperature range 254 to 283 K at 1 atm pressure of N 2 by Fourier transform infrared spectroscopy. A heterogeneous reaction of NO 2 and H 2 O 2 was used to generate HO 2 NO 2 with less than 20% HNO 3 and less than 5% NO 2 present as impurities. The HO 2 NO 2 had lifetimes of 5 to 20 h in our chamber, presumably determined by heterogeneous loss to the walls. Two paths have been proposed for the reaction of NO 2 with HO 2 : (1), NO 2 + HO 2 → HONO + O 2 (2). In this study the ratio k 1 / k 2 was calculated to be greater than 10 3 throughout the temperature range studied. The homogeneous unimolecular decay of the HO 2 NO 2 , reaction (3), was investigated by adding excess NO in order to remove HO 2 by reaction (4). (3), HO 2 + NO → NO 2 + OH (4). The rate constant k 3 was determined to be 1.4 × 10 14 exp(−20700 ± 500/ RT )s −1 . The thermal decomposition lifetimes of HO 2 O 2 at 1 atm total pressure calculated from k 3 are 12 s at 298 K, 5 min at 273 K and 1 month at 220 K. Implications of these results for the role of pernitric acid in the lower and upper atmosphere are discussed.

Pressure and temperature dependence of the unimolecular decomposition of HO2NO2

The pressure and temperature dependence of the unimolecular decomposition of pernitric acid HO2NO2→NO2+HO2 have been studied in the presence of excess nitric oxide by Fourier transform infrared spectroscopy in a 5800 liter, Teflon‐lined chamber over the temperature range 261 to 295°K with N2 or O2 pressures between 1 and 760 torr. The rate constant in the second‐order kinetic regime was determined to be 5.2×10−6 exp[−19 900±500/RT] cm3 molecule−1 sec−1 for N2 pressures up to ∼7 torr. The pressure dependence of the reaction between the second‐order region and 1 atm pressure was determined for N2 and O2 at 278°K and for N2 at 261°K and fitted to an empirical rate constant expression for use in atmospheric modeling calculations. Extrapolation of the data at 278°K gave a limiting first‐order high pressure rate constant of ∼0.018 sec−1. The relative efficiency of O2 as an M gas relative to N2 (1.0) between 1 and 760 torr was 0.83±0.12. The implications of these results for the reaction of HO2 with NO2 and for ...