N2O5 chemistry

When NMHC are significant in concentration, differences in their oxidation mechanisms such as how the NMHC chemistry was parameterized, details of R02-/R02 recombination (95), and heterogenous chemistry also contribute to differences in computed [HO ]. Recently, the sensitivity of [HO ] to non-methane hydrocarbon oxidation was studied in the context of the remote marine boundary-layer (156). It was concluded that differences in radical-radical recombination mechanisms (R02 /R02 ) can cause significant differences in computed [HO ] in regions of low NO and NMHC levels. The effect of cloud chemistry in the troposphere has also recently been studied (151,180). The rapid aqueous-phase breakdown of formaldehyde in the presence of clouds reduces the source of HOj due to RIO. In addition, the dissolution in clouds of a NO reservoir (N2O5) at night reduces the formation of HO and CH2O due to R6-RIO and R13. Predictions for HO and HO2 concentrations with cloud chemistry considered compared to predictions without cloud chemistry are 10-40% lower for HO and 10-45% lower for HO2. 

For a review of N2O5 see Fischer, J.W. in Feuer Nielsen Nitro Compounds, Recent Advances in synthesis, and Chemistry VCH NY, 1990, p. 267. 

N2O5 acts as a reservoir species in atmospheric chemistry making NO3, formed by the dissociation of N2O5, the major nighttime oxidant in the stratosphere. 

Atkinson, Pitts, and coworkers at the University of California at Riverside are in the process of publishing a series of papers on NO3 chemistry. I will briefly describe a few of their results. Their method involves the use of a smog chamber experiment with long path infrared absorption measurements of reactant concentrations [26]. Their kinetic measurements are based on the competition between two different reactants for the NO3 radical. N2O5 is used as a source of NO3. Table 2 summarizes some of their data for reactions of NO3 with selected organic compounds. Most of these materials are present in significant concentrations only in polluted urban environments. For the alkene compounds the rate coefficients follow the general trend found few the addition reactions of O and OH. This supports the proposal that the mechanism involves addition to the double bond. A dramatic increase in reactivity is observed with the... 

These processes accelerate the conversion of the first hydrated water cluster ion to the second. It should be noted that Reaction (7.70) converts N2O5 to HN03. Bohringer et al. (1983) have shown that this process is probably not fast enough to be important in stratospheric neutral chemistry, however. 

It would be convenient if the kinetic reaction profile in Figure 5.2 could be used directly, without the need for any further processing of the data, to obtain information about the experimental rate equation for the decomposition of N2O5. In fact, a preliminary check can be carried out using a method based on the idea of reaction half-life, which is denoted by fi/2. This approach was suggested many years ago by Wilhelm Ostwald who was Professor of Chemistry at Leipzig (1887-1906) and a Nobel prizewinner (1909). 

The effect of reaction 4.27 on gas-phase stratospheric chemistry is as follows. The conversion of a reservoir species N2O5 into a relatively stable species HNO3 serves to remove NO2 from the active catalytic NO system, reducing the effectiveness of O, destruction by the NO, cycle. The reduction in NO2, on the other hand, decreases the formation of CIONO2, allowing more CIO to accumulate than in the absence of reaction 4.27. More CIO means that the effectiveness of the CIO, cycles is increased. Although photolysis of HNO, with the H atom derived from aerosol H2O, provides an additional source of HO, to the system, reaction 4.27 is not predicted to have a major effect on the HO, cycles. 

FIGURE 4.24 (a) Calculated profiles for HNO, NO2, and NO (solid lines) and N2O5 (dashed line) for the ATMOS simulation at 47° S, sunrise, assuming gas-phase chemistry only (McElroy et al., 1992). ATMOS data are indicated by the circles, which have been connected by dotted lines for convenience of interpretation. Error bars represent the lo- estimate of the measurement uncertainty, (b) Same as for part (a) except the simulation includes the heterogeneous hydrolysis of N2O, proceeding with an efficiency of y = 0.06. Reprinted from McElroy et al. (1992) with kind permission from Elsevier Science Ltd., The Boulevard, Langford Lane, Kidlington 0X5 1GB. UK. 

The synthesis and chemistry of platinum nitrates has been recently reviewed. The only homoleptic nitrate complex is K2Pt(N03)g formed from K2PtBre and N2O5. Oxidation of the nitrito complex K2Pt(N02)4 gives K2Pt(N02)6> and not the nitrate complex. 

Flourocarbon and Related Chemistry (warm to 25 °C) N2O5, COF2, and CF3I (but no... 

Equation (16.14) illustrates a characteristic of first-order reactions the concentration of the reactant decreases exponentially with time (compare dashed curve in Fig. 16.4). The paradigm for this kind of process is radioactive decay, but all monomolecular elementary reactions such as the rearrangement of cyclopropane into propane in the gas phase are included in this. There are many further decomposition reactions to be found in classical chemistry, such as decomposition of dinitrogen pentaoxide N2O5 in the gas phase according to... 

Chang, T. Y., Kuntasal, G. and W. R. Pierson (1967) Night-time N2O5/NO3 chemistry and nitrate in dew water. Atmospheric Environment 21, 1345-1351 Chapman, S. (1930) A theory of upper atmosphere ozone. Memoirs of the Royal Meteorological Society 3, 103-109... 

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