Are Primary Quantum Yields of NO2 Photolysis at λ ≤ 398 nm Smaller than Unity?

Abstract

Primary quantum yields Φ of NO2 photolysis at wavelengths λ Յ 398 nm and at bath gas pressures below 1 bar are analyzed. Stern-Volmer plots for collisional photolysis quenching, from experiments at pressures between 10 and 1000 bar, do not indicate a substantial reduction of the quantum yield below unity for pressures below 1 bar. The consequences of the recently discovered fluctuations of specific rate constants k(E) for NO2 dissociation on collisional photolysis quenching are analyzed. These effects can lead to a small reduction of Φ at pressures below 1 bar which, however, is also smaller than the reduction reported in some experiments. Reanalysis of these experiments shows instead that, apart from experimental artifacts, the influence of the secondary reactions O ϩ NO2 (ϩ M) → NO3 (ϩ M), NO3 ϩ NO → 2 NO2, and O ϩ NO2 → O2 ϩ NO was underestimated. As a consequence, all experimental evidence so far is in favour of a low pressure primary quantum yield which is unity over the complete wavelength range 300Ϫ 398 nm. This leads to a revised recommendation of quantum yields Φ for the range 300Ϫ 430 nm at 298 K and 248 K. A revision of the limiting low pressure rate constant at 298 K of the reaction O ϩ NO2 ϩ N2 → NO3 ϩ N2 of (1.6 Ϯ0.2) ϫ10 Ϫ31 [N2] cm 3 molecule Ϫ1 s Ϫ1 is also recommended (to be employed together with Fc ϭ 0.6 and a limiting high pressure value of 2.2ϫ 10 Ϫ11 cm 3 molecule Ϫ1 s Ϫ1 ).

Actinometric measurements of NO<sub>2</sub> photolysis frequencies in the atmosphere simulation chamber SAPHIR

“…In the case of NO 2 photolysis the agreement is even within 5% in a study from our laboratory (Kraus et al, 2000) using molecular data σ (NO 2 ) and φ(O 3 P) by Merienne et al (1995) and Troe (2000), respectively, as recently recommended by Atkinson et al (2004).…”

Light induced conversion of nitrogen dioxide into nitrous acid on submicron humic acid aerosol

“…From the measured spectral actinic flux at full intensity (7 lamps illuminated), known absorption spectra, and quantum yields (Bongartz et al, 1994;Merienne et al, 1995;Troe, 2000), the photolysis frequencies of HONO and of NO 2 in the reactor are calculated as 5.8×10 −5 s −1 and as 5.5×10 −4 s −1 , respectively. This calculated photolysis frequency of NO 2 is close to the measured value of 5.2×10 −4 s −1 (see Fig.…”

Calibration and evaluation of CCD spectroradiometers for ground-based and airborne measurements of spectral actinic flux densities

“…Compared to a reference temperature of 298 K, in this example, j (O 1 D) and j (NO 2 ) are on average smaller by factors of 0.73 and 0.92, respectively. These numbers are based on the temperature dependence of the molecular data from the literature (Daumont et al, 1992;Matsumi et al, 2002;Merienne et al, 1995;Troe, 2000) and demonstrate the importance of ambient temperature for aircraft measurements.…”