Nitrate radical reactions

Cresols degrade rapidly in air. Removal during the day is dominated by the reaction with hydroxyl radical (HO-), while nighttime removal is probably dominated by the nitrate radical. Reaction with other oxidants in air (e.g., ozone) will be much slower than reactions with hydroxyl or nitrate radical (Atkinson and Carter 1984). 

The kinetics and mechanisms of nitrate radical reactions with alkanes and a variety of other organics relevant to the atmosphere are discussed in detail in two excellent reviews by Wayne et al. (1991) and Atkinson (1991). The kinetics of the N03-alkane reactions are summarized in Table 6.3, where it can be seen that, with the exception of methane, they are in the range 10 lX-10 lf cm3 molecule-1 s-1. 

While these reactions are much slower than the corresponding OH reactions, the nighttime peak concentrations of NO, under some conditions are much larger than those of OH during the day, 400 ppt vs 0.4 ppt. Even given the differences in concentration, however, as seen from the lifetimes in Table 6.1, the nitrate radical reaction is still relatively slow. While the removal of the alkanes by NO, is thus not expected to be very significant under most tropospheric conditions, reaction (20) can contribute to HNO, formation and the removal of NOx from the atmosphere. 

Field studies suggest that the nitrate radical reaction can also be a major contributor to isoprene decay at night, as well as contributing to the formation of organic nitrates in air. For example, Starn et al. (1998b) found that when the product of N02 and 03 (which form N03) was high in a forested region in the southeastern United States, isoprene often decayed rapidly at dusk. This reaction of N03 with isoprene was estimated to be the major sink for N03 under some conditions in this area. 

Seisel S., Fliickinger B., Caloz F., and Rossi M. J. (1999) Heterogeneous reactivity of the nitrate radical reactions on halogen salt at ambient temperature and on ice in the... 

Nitrate radical reactions are the dominant nighttime loss process for biogenics in the troposphere. The room-temperature (298 K) rate con-... 

Limited product data are available for the nitrate radical reaction with isoprene and a- and /3-pinene. For the isoprene reaction, Barnes et al. (1990) determined molar yields of total nitrates of 80%, CO of 4%, and formaldehyde of 11%. Methacrolein was also detected, but an accurate product yield could not be determined. Additional work with a- and /3-pinene was not conclusive. Although nitrate features were observed as initial reaction products, these compounds quickly transferred into aerosols, thus preventing identification via the methods employed in the study (FTIR spectroscopy). 

This work was intended to give information about non-photochemical processes affecting species that are involved in hydrocarbon oxidation and ozone formation, such as the hydrocarbons themselves or the active nitrogen compounds. The main part of the work was concerned with rates and products in nitrate radical reactions with various hydrocarbons. Some interest was also taken in purely inorganic reactions. 

Table 1 Rate coefficients or rate coefficient expressions for nitrate radical reactions. When no temperature expression is given the value refers to room temperature.

Nitrate radical reactions Interactions with alkynes,... 

An experimental study of some nitrate radical reactions of importance to atmospheric chemistry. 

Dlugokencky, E.J., Howard, C.J. Studies of nitrate radical reactions with some atmospheric organic compounds at low pressures. J. Phys. Chem. 93, 1091-1096 (1989)... 

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