Peroxy ethoxyformyl nitrate, a new peroxynitrate of possible atmospheric existence.

ADRIANA G. BOSSOLASCO; FABIO E. MALANCA; GUSTAVO A. ARGÜELLO

Grenoble

Conferencia; European Research Course on Atmospheres- ERCA 2011; 2011

The peroxynitrates (ROONO2) are species that can be formed during the degradation of compounds released into the atmosphere, and act as reservoir species for either ROO. or NO2 radicals. Due to the increase of their stability as the temperature decreases, their atmospheric lifetimes are about days at the lower troposphere and years near the tropopause.Only some peroxy acyl nitrates (RC(O)OONO2) have been detected and measured in the atmosphere. Among them, we could cite peroxy acetyl (PAN); propionyl (PPN) and benzoyl (PBzN) nitrates. These molecules are formed in the atmospheric degradation of hydrogenated volatile organic compounds. In similar way, the atmospheric oxidation of ethyl formate, an organic compound used as fumigant and pesticide, could lead to the formation of peroxy ethoxyformyl nitrate (CH3CH2OC(O)OONO2, PEFN).PEFN was synthesized from the irradiation of a mixture of ethyl formate (EF), Cl2, NO2 and O2 at 253 K using black lamps to initiate the chlorine molecule´s rupture, and the subsequent oxidation of EF. PEFN was purified by successive trap-to-trap distillation. Between 173 and 87 K was possible to eliminate the more volatile fraction containing ClNO, ClNO2, CO2 and HCl. Subsequent distillations between 198 K and 153 K mainly allowed the extraction of EF and C2H5ONO2. The more volatile fraction containing PEFN, PAN and HC(O)OH as well as the remnant EF was treated between 213/223 K to 153 K, leading to the elimination of PAN, EF and formic acid. The resulting sample contained about 95% of PEFN.This new peroxynitrate was characterized by IR and UV spectroscopies. The infrared bands (cm-1) and their corresponding absorption cross-sections (cm2molec-1) are 1831 (0.44x10-18), 1744 (0.93x10-18), 1308 (0.23x10-18), 1224 (1.24x10-18), 973 (0.15x10-18) and 793 (0.32x10-18). Thermal decomposition was studied between 301 and 279 K adding NO to the sample, at total pressures of 1 atm by addition of N2. The kinetic parameters obtained are Ea = 108 ± 5 kJmol-1 and A = 1.2x1016s-1. They are similar to those obtained for other peroxy acyl nitrates. Consequently, PEFN could also be formed and transported in the atmosphere, especially if it reaches the regions of the free troposphere where lower temperatures further stabilize this molecule.Atmospheric photochemical lifetimes were calculated using the TUV 4.2 program as a function of altitude and solar zenith angle, taking into account our experimental data for the UV absorption cross-sections. The results show that from the surface to 4 Km height, photochemical lifetimes range between 6 to 20 days, meanwhile thermal lifetime goes from hours at the surface to several months at the tropopause height. Beyond the tropopause, photochemical mechanisms take over.Taking into account that: (a) EF is emitted into the atmosphere, (b) its gas-phase oxidation in the presence of high NO2 concentrations leads to the PEFN formation and (c) the lifetimes of PEFN are similar to other peroxynitrates of atmospheric existence; we conclude that it could be possible the atmospheric existence of this new peroxynitrate.