No abstract

No abstract

Results are presented from an extensive theoretical investigation aimed at evaluating the effect of molecular multiple scattering and surface albedo on photodissociation rates. Results are compared with similar calculations typical of most atmospheric photochemical models which only describe absorption in a direct solar beam. The effect of molecular multiple scattering and surface albedo on photodissociation rates, which can be sizable, depends strongly on solar zenith angle, surface albedo, altitude, and wave‐length regime. Various atmospheric photodissociation processes are categorized by spectral type based upon the wavelength regime in which the photodissociation process occurs. Three basic wavelength regimes are noted, and results characteristic of each regime are presented. Adjustment factors are provided for generalizing the pure absorption calculations.

No abstract

Publication costs assisted by Science Applications Incorporated Some current developments in tropospheric photochemical analysis are discussed, and advanced computational aids that facilitate this analysis are indicated. Photochemical emphasis is on the coupled NO,, SO,, ECO, mechanisms governing oxidant and sulfur chemistry in the ambient atmosphere, in some cases distinct from smog chamber environments. The recent breakdown (by Trijonis and Arledge) of urban hydrocarbon sources to their individual organic components is applied to generate an improved description of aggregated hydrocarbons in atmospheric photochemical mechanisms. The objective of this study is to better identify and understand internal mechanistic pathways for tropospheric cycles, with special attention devoted to detailed roles of reactive intermediate species such as H02, OH, and organic free radicals. We also probe the significance to the overall mechanism of uncertain reaction rates and reaction product pathways including H02, NO, RO, R02, stable nitrates, stable ozonides, peroxy nitric acid, ketones, and photolytic processes appropriate to multiday analysis. The computational aspects of this mechanism analysis include the application and description of automated photochemical kinetics codes, reaction screening and editing routines, and systematic reaction sensitivity analysis.The purpose of these computational tools is to relieve the scientist of dispensable bookkeeping manipulations that are tedious, error prone, and excessively time consuming. It is found that well-conceived and applied computational aids of these types substantially assist the normal intuitive processes of the scientist as well as markedly increasing available time and personal energy for creative thought.