Anthony H. McDaniel

The temperature dependent, infrared absorption cross-sections for the chlorofluorocarbons: CFC-11, CFC-12, CFC-13, CFC-14, CFC-22, CFC-113, CFC-114, and CFC-115

The infrared absorption cross-sections for eight commonly used halogenated methanes and ethanes have been measured as a function of temperature from 203 to 293 K. High resolution spectra (0.03 cm-1) have been used to derive integrated band strengths and peak cross-sections associated with the spectral features in the infrared region from 600 to 1500 cm-2. The values obtained in this study are compared to those from previous reports, and recommendations are made for uses in atmospheric sensing and radiative energy transfer models. The observed temperature dependence in the spectral features is also discussed.

Actinometer and Eppley radiometer measurements of the NO2 photolysis rate coefficient during the Mauna Loa Observatory photochemistry experiment

Measurements of the apparent first-order rate coefficient for NO2 photodissociation (jNO2) were made using a chemical actinometer during the month of May 1988 at the Mauna Loa Observatory, Hawaii. Simultaneous measurements of the ultraviolet irradiance (E), obtained with an Eppley radiometer, allowed extensive testing of the semi-empirical relationships between E and jNO2 proposed by Madronich (1987a). More than 3700 simultaneous measurements of jNO2 and E were obtained for solar zenith angles ranging from 4–90 degrees, and for different sky conditions (including clear skies, partial cloud cover, arid valley clouds below the horizon). For overhead clear skies, the NO2 photodissociation rate coefficient derived from Eppley radiometer data, here denoted j′, was in good agreement with actinometric measurements, j′/jNO2=1.01±0.05(1σ). The actinometer-radiometer relationship holds reasonably well even when low-lying valley clouds are present. For the periods of overhead intermittent clouds, the j′values track jNO2 values well, but the observed ratio shows significantly more scatter and the average is somewhat less than unity: 0.93 ± 0.09 (1σ). Measurements taken with and without upward scattered and reflected radiation show that valley clouds can contribute to the jNO2 values for the conditions encountered during the Mauna Loa Observatory Photochemistry Experiment.

An improved chemical amplifier technique for peroxy radical measurements

The chemical amplifier for atmospheric peroxy radical measurements, first described in the early 1980s has been improved relative to these earlier reports. The details of the instrument and a new radical calibration procedure are discussed as they relate to participation in a field study in the southeastern United States in the summer of 1990. The theoretical behavior of the chemical amplifier is also examined with the use of analytical solutions to the relevant kinetic equations as well as with a numerical model. Several issues of atmospheric relevance are addressed including the response of the instrument to organic peroxy radicals, interferences from PAN and peroxynitric acid, accuracy, precision, and detection limits studied through a number of laboratory and field investigations. Some new findings realized since the summer of 1990 are also included. 44 refs., 16 figs., 2 tabs.

Infrared absorption cross sections for N2O5

Abstract Laboratory measurements of absolute infrared absorption cross sections for three strong bands of N 2 O 5 have been made as a function of temperature from 233 to 350 K. The results of this study confirm most of the recent laboratory studies, indicating reasonable confidence in cross sections for this molecule which are of potential use in its identification and measurement in the atmosphere and in laboratory systems. Beer-Lambert linearity is confirmed and the effect of instrumental resolution on integrated intensities as well as peak cross sections is reported.

The equilibrium constant for N2O5⇄NO2+NO3: Absolute determination by direct measurement from 243 to 397 K

The equilibrium constant for N2 O5 ⇄NO2 +NO3 [reaction (1)], has been determined through direct concentration measurements of N2 O5, NO2, and NO3 in a temperature controlled long path cell, using absorption spectroscopy in the infrared and visible regions from 243 to 397 K. The results give K1C =1.30×1026  exp(−21 490/RT) molecules cm−3 with an estimated overall uncertainty of 30% at the 95% confidence level. This results in an equilibrium constant near room temperature approximately one‐half that of previously accepted values. Using the temperature dependence of the equilibrium constant and new data for the enthalpy of formation of gaseous N2 O5 yields an enthalpy of formation for NO3 of 15.39±0.72 kcal mol−1. In additional experiments the temperature dependent first order decay rates of N2 O5 were determined from which a value for the product of the equilibrium constant (K1C ) and the rate constant for reaction (2): NO2 +NO3 →NO+NO2 +O2 was obtained for temperatures from 298 to 396 K: K1 k2 =1.23×1013  ...