Atmospheric fate of several alkyl nitrates Part 2UV absorption cross-sections and photodissociation quantum yields

Abstract

The UV absorption cross-sections of methyl, ethyl and isopropyl nitrate between 233 and 340 nm have been measured using a diode array spectrometer in the temperature range 240È360 K. The absorption cross-sections of these alkyl nitrates decrease with increasing wavelength and decrease with decreasing temperature for j [ 280 nm. The photodissociation quantum yield for to produce and was found to be essentially unity at 248 nm using transient UV absorption methods. CHand H atoms in the photodissociation of methyl nitrate at 248 and 308 nm were found to be negligible using resonance Ñuorescence detection of the atoms. High quantum yields for O atoms were measured following 193 nm photolysis of methyl nitrate. The OH radical was measured to be a photoproduct with a very small quantum yield. Using the OH rate coefficients reported in the accompanying paper and the UV absorption cross-sections and the photodissociation quantum yields measured here, the Ðrst-order rate constants for atmospheric loss of methyl, ethyl and isopropyl nitrate were calculated. Photolysis was found to be the dominant atmospheric loss process for the three alkyl nitrates.

Levels and pattern of volatile organic nitrates and halocarbons in the air at Neumayer Station (70°S), Antarctic

“…While for alkyl mononitrates 6 C5 the dominant loss process is photolysis (8) (Clemitshaw et al, 1997), alkyl nitrates with more than five C-atoms and multifunctional alkyl nitrates are mainly degraded by OH radicals (9) (Talukdar et al, 1997).…”

Interferences in photolytic NO<sub>2</sub> measurements: explanation for an apparent missing oxidant?

“…It is also shown that there is minimal overlap with HONO and no overlap in the spectrum at all with PAN. It has been shown (Carbajo and Orr-Ewing, 2010;Talukdar et al, 1997) that there is no overlap with methyl, ethyl, or isopropyl nitrate -methyl nitrate being a minor impurity in PAN synthesis. There is only very minor overlap in the PLC optics spectrum with PAN, methyl ethyl, and isopropyl nitrate.…”

Quantum Yields for Photochemical Production of NO2 from Organic Nitrates at Tropospherically Relevant Wavelengths

“…The data were obtained using the 13-cm pathlength gas cell described in section 2, at a temperature of 294 K. Spectra were recorded typically for 4 different pressures of each alkyl nitrate from 1.5 -17 Torr, with at least three scans per pressure, and the absorption cross sections plotted are the averages of values nitrate from the current work (black) and reference [15] (red); (b) methyl nitrate (black) and n-propyl nitrate (red); (c) isopropyl nitrate (black) and dinitrate A (red), with the latter spectrum from reference [7]. All spectra from the current study were recorded at a temperature of 294 K.…”

“…[13][14][15] Photochemical destruction of RONO2, RONO2 + h  RO + NO2 (1) releases NOx into the atmosphere and thus contributes to further propagation of the HOx and NOx cycles. RONO2 photolysis to liberate NO2 is generally assumed to occur with quantum yield (Φ 2 ) values of unity, 2-3, 13, 16-18 but to date there has been only limited experimental verification.…”

“…RONO2 photolysis to liberate NO2 is generally assumed to occur with quantum yield (Φ 2 ) values of unity, 2-3, 13, 16-18 but to date there has been only limited experimental verification. 3,15,[19][20][21][22] Here, we focus on measurements of quantum yields for NO2 from process (1) following photo-excitation of RONO2 at UV wavelengths appropriate for the Earth's troposphere (290 nm). At these wavelengths, absorptions occur via weak *n transitions centred on the -ONO2 group, and the spectral bands extend to wavelengths around 330 nm.…”