NO3 HCHO

Measurements of rate constants of the reaction of NO3 with HCHO and CH3CHO are scarce. The lUPAC subcommittee (Atkinsrai et al. 2006) recommends the rate constants at 298 K for the reactirais of HCHO and CH3CHO as ksjoe (298 K) = 5.6xl0 , and ks,07 (298 K) = 2.7xl0 cm molecule s respectively, based on Cantrell et al. (1985) using DOAS for the direct measurement of NO3. The measurement of temperature dependence has been made only for reaction (5.107) with CH3CHO, and the lUPAC subcommittee (Atkinson et al. 2006) recommends 

5 Homogeneous Elementary Reactions in the Atmosphere and Rate Constants 

Quantum chemical calculations for the reactions of NO3 with HCHO and CH3CHO has been made by Mora-Diez and Boyd (2002), and the transition states and their energy levels for the H-atom abstraction reaction (5.106) and (5.107) has been obtained. The activation energy for the reaction of CH3CHO obtained theoretically is 18.5 kJ moP, which agrees reasonably well with the experimental value of 15.6 kJ moP  

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Gas phase component concentrations A number of standard gas analysers are routinely available for determination of gaseous mixing ratio of CH4, CO, O3, NO, NO2 and SO2 at moderate atmospheric concentrations. GC determination of a limited number of NMHC species is also available for appropriate experiments. An Aerodyne Quantum Cascade Tunable Diode Laser Absorption Spectrometer (QC-TDLAS) is periodically available for NH3 measurements using tiie line at 967 cm and for NO2 measurement at 1606 cm . There are several potential experiments which may benefit from measurement of other trace species. The Differential Optical Absorption Spectrometer (DOAS) described below may be used for determination of lO, OIO, BrO, NO3, HCHO, SO2 and other trace species. 

During SOAPEX-2, measurements of the free-radicals OH, HO2, HO2+XRO2, NO3, IO and OIO were supported by measurements of temperature, wind speed and direction, photolysis rates (j D) and j(N02)), water vapor, O3, HCHO, CO, CH4, NO, NO2, peroxyacetyl nitrate (PAN), a wide range of NMHCs, organic halogens, H2O2, CH3OOH and condensation nuclei (CN). 

Among the manifold reactions in snow the photolysis of nitrate (NO3 ) is now the best characterized reaction due to a range of laboratory experiments. These studies have been used to extract information about the absorption coefficients and quantum yields of NO3 in ice as a function of wavelength, the formation of products like the hydroxyl radical (OH) and nitrite (N02), and the release of NOx to the gas phase. Limited information regarding the absorption coefficients and the formation of OH radicals can also be found for the photolysis of H202. " Investigations regarding the photolytic decomposition of further compounds with a potential relevance for photochemical processes in surface snow are limited to studies, in which reactions of HCHO and NO2 have been examined. 

Equation 10 is used to calculate the dry deposition velocity for NO2. It is assumed that all of the N02 in the dew came from the dissolution of NO2. A value of 0.03 cm/s is found for the deposition velocity. To calculate the dry deposition velocity for HNO3, it is assumed that the source of dew N03 was the dry deposition of HNO3. The calculated value, 2.0 cm/s, appears high relative to the velocities of other soluble gases such as HCHO (see Tables II and IV) and likely reflects that HNO3 can be adsorbed onto a dry surface. Evidence to substantiate this point appears in the next section. It is also possible that some of the NO3 and/or NO2 arose from the deposition of small amounts of PAN however, the ionic fate of dissolved PAN is not known and therefore more information is required for an assessment of its role in atmospheric corrosion. 

Several pathways for S(IV) transformation to S(VI) have been identified involving reactions of S(IV) with O3, H2O2, Oz (catalyzed by Mn(II) and Fe(III)), OH, SO5, HSO5, S04, PAN, CH3OOH, CH3C(0)00H, H02, NO3, NOa, N(III), HCHO, and Cl2 (Pandis and Seinfeld 1989a). There is a large literature on the reaction kinetics of aqueous sulfur chemistry. We present here only a few of the most important rate expressions available. 

Further studies of the reaction between NO3 and CH3O2 using a discharge flow coupled with mass spectrometry and studies and the photo-oxidants of HCHO, CH3CHO and CO2 are reported by Moortgat elsewhere in this report. 

For NO3 + dialkenes (butadiene), the identified products were CO (4%), HCHO (12%) acrolein CH =CH-CHO (12%), total nitrates (60%). For the NO3 + isoprene reaction, yields of products were CO (4%), HCHO (11%), methacrolein CH3=CH(CH3)-CHO (uncertain yield), and total nitrates (80%). The aldehydes formed in the reactions of NO3 with the dialkenes can be explained by the thermal decomposition of the related nitrooxy-alkoxy radicals as in reaction (Equation 4.85) for monoalkenes. The formation of small quantities of CO in both the NO3 + dialkenes reaction systems is difficult to explain. It is unclear whether the CO is formed directly in the reaction of NO3 with dialkenes or whether it is a product of secondary reactions of NO3 with acrolein or methacrolein. 

Other Oxides of Nitrogen (NO2, NO3, N2O5, HNO3, HO2NO2), Hydrogen peroxide (H2O2), Formaldehyde (HCHO)... 

NO3 reacts with aldehydes other than alkenes among organic compounds. Since HO2 radicals are formed from acyl radicals (RCO) generated in the reaction, the NOs-aldehydes reactions are important as HO and HO2 radical source at nighttime. In this paragraph, the reactions of NO3 with HCHO and CH3CHO are described as representative example of aldehydes. 

The reactions of NO3 and aldehydes are H atom abstraction from aldehyde group. In the case of HCHO and CH3CHO, the reactions proceed as. 

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