Night-time radical chemistry during the TORCH campaign

We present one of the most comprehensive studies of night-time radical chemistry to date, from the Tropospheric ORganic CHemistry experiment (TORCH) in the summer of 2003. TORCH provided a wealth of measurements with which to study the oxidizing capacity of the atmosphere. The measurements provided input to a zero-dimensional box model which has been used to study night-time radical chemistry during the campaign. Average night-time predicted concentrations of OH (2.6 × 10⁵ molecule cm^?3), HO₂ (2.9 × 10⁷ molecule cm^?3) and [HO₂+ΣRO₂] radicals (2.2 × 10⁸ molecule cm^?3) were an order of magnitude smaller than those predicted during the daytime. The model under-predicted the night-time measurements of OH, HO₂ and [HO₂+ΣRO₂] radicals, on average by 41%, 16% and 8% respectively. Whilst the model captured the broad features of night-time radical behaviour, some of the specific features that were observed are hard to explain. A rate of radical production assessment was carried out for the whole campaign between the hours of 00:00 and 04:00. Whilst radical production was limited owing to the absence of photolytic reactions, production routes via the reactions of alkenes with O₃ provided an effective night-time radical source. Nitrate radical concentrations were predicted to be 0.6 ppt on average with a peak of 18 ppt on August 9th during a polluted heat wave period. Overall, the nitrate radical contributes about a third of the total initiation via RO₂, mostly through reaction with alkenes.     

Oxidative dealkylation of five phenylurea herbicides by the fungus CunninghamellaechinulataThaxter

Microorganisms isolated from soil degrade phenylurea herbicides via two major pathways: (i) direct hydrolysis by an amidase leading to N,O-dimethylhydroxylamine, CO₂ and aniline¹ and (ii) N-dealkylation, which has been described as the first step in urea herbicide degradation by a variety of organisms including mammals, plants and microbial systems (for a review see reference 2).Until now no attempts have been made to investigate the mechanism of N-demethylation of substituted ureas in soil microorganisms, due to the instability of the N-hydroxymethyl intermediates. This reaction mechanism has only been described in detail in green plants^3–5. As among soil fungi Phycomycetes are known to demethylate phenylurea herbicides^6,7 this study has been made to identify intermediate hydroxymethyl compounds from urea herbicides, when incubated with the fungus $\text{Cunninghamella echinulata Thaxter}$.