NEAR UV ABSORPTION-SPECTRA AND PHOTOLYSIS PRODUCTS OF DIFUNCTIONAL ORGANIC NITRATES - POSSIBLE IMPORTANCE AS NO(X) RESERVOIRS

Difunctional organic nitrates are important products of the atmospheri c reaction of NO3 radicals with unsaturated hydrocarbons about which r elatively little is known. In a continuation of the investigation of t he atmospheric chemistry of such compounds, the UV absorption spectra of the following organic dinitrates and keto nitrates have been quanti tively measured in the gas phase at 298 +/- 2 K and atmospheric pressu re: 1,2-propandiol dinitrate, CH3CH(ONO2)CH2(ONO2); 1,2-butandiol dini trate, CH3CH2CH(ONO2)CH2(ONO2); 2,3-butandiol dinitrate, CH3CH(ONO2)CH (ONO,)CH3; cis 1,4-dinitrooxy-2-butene, CH2(ONO2)CH-CHCH2(ONO2); 3,4-d initrooxy-1-butene, CH2(ONO2CH(ONO2)CH=CH2; alpha-nitrooxy acetone, CH 3COCH2(ONO2); 1-nitrooxy-2-butanone, CH3CH2COCH2(ONO2); 3-nitrooxy-2-b utanone, CH3CH(ONO2)COCH3. Although the UV spectra of the nitrates are all very similar in shape those of the keto nitrates are red-shifted compared to the dinitrates and in the spectral range of atmospheric in terest (lambda > 290 nm) their absorption cross-sections are approxima tely a factor of 5 higher. The cross-sections of the dinitrates are a factor of 2 higher than those reported in the literature for the corre sponding alkyl mononitrates. The UV absorption cross-sections of the d ifunctional nitrates were used in combination with solar actinic flux data to estimate photolysis frequencies and consequently atmospheric l ifetimes for these compounds. The results indicate that for the satura ted difunctional nitrates studied in this work photolysis will general ly be somewhat some important than reaction with OH radicals as an atm ospheric removal process. However, for unsaturated nitrates loss due t o reaction with OH will dominate over photolysis as an atmospheric sin k. Preliminary FT-IR analyses of the photolysis products of alpha-nitr ooxy acetone, 3-nitrooxy-2-butanone and 2,3-butandiol dinitrate using both mercury and fluorescent lamps indicate that NO2 is released in th e primary step. The further reactions of the radicals thus produced re sult in the formation of CO, aldehydes and PAN. The possible significa nce of the results for difunctional organic nitrate as reservoirs for reactive odd nitrogen NO(y) in the atmosphere, especially during the n ight, is briefly discussed.