Relative Tropospheric Photolysis Rates of Acetaldehyde and Formaldehyde Isotopologues Measured at the European Photoreactor Facility

Abstract

The photolysis rates of HCHO, DCDO, CH(3)CHO, and CH(3)CDO are studied by long-path FTIR spectroscopy in natural tropospheric conditions at the European Photoreactor Facility (EUPHORE) in Valencia, Spain. Average relative photolysis rates j(HCHO)/j(DCDO) = 3.15 +/- 0.08 and j(CH(3)CHO)/j(CH(3)CDO) = 1.26 +/- 0.03 are obtained from three days of experiments for each reaction in the period June 17 to July 7, 2006.

Pressure dependent isotopic fractionation in the photolysis of formaldehyde-d<sub>2</sub>

“…In Fig. 4 the relative removal rates are plotted as a function of chamber pressure, including the atmospheric pressure results from the studies at the European Photoreaction Facility (Feilberg et al, 2005b(Feilberg et al, , 2007aNilsson et al, 2009a), and the results from the study on HDCO (Nilsson et al, 2010). The present results at 1000 mbar are in agreement with the results from the previous studies, an agreement that was also seen for the HDCO isotopologue (Nilsson et al, 2010).…”

“…Closed triangles represent the corresponding values for the HDCO isotopologue, from Nilsson et al (2010). Open symbols are previous determinations of k(H 2 CO)/k(D 2 CO) from Feilberg et al (2005bFeilberg et al ( , 2007a, triangle, and Nilsson et al (2009a), circle. Lines represent the calculated isotope effects.…”

“…For an evaluation of the HDCO results we refer to the discussion in Nilsson et al (2010). The kinetic isotope effects for photolysis of dideutero formaldehyde have been determined in two studies at the European Photoreactor Facility (Feilberg et al, 2005b(Feilberg et al, , 2007aNilsson et al, 2009a); the results are in reasonable agreement and are presented in Table 1.…”

Tropospheric Photolysis Rates of the Acetaldehyde Isotopologues CD3CHO and CD3CDO Relative to CH3CHO Measured at the European Photoreactor Facility

“…In addition, it has been proposed that acetaldehyde may be a significant source of atmospheric acids, helping to explain the gap between measurements and models. Examination of the absorption cross sections of the acetaldehyde isotopologues 23 shows that only a few percent of the observed photolytic kinetic isotope effects (j CH3CHO /j CD3CHO = 1.10 ± 0.10, j CH3CHO / j CH3CDO = 1.26 ± 0.03 (see ref 7) and j CH3CHO /j CD3CDO = 1.75 ± 0.04) is due to the differing rates of photoexcitation. The explanation seems rather to involve isotope-dependent changes in the unimolecular lifetimes of the isotopologues and their rates of collisional quenching, resulting in pressure and isotopologue-dependent changes in the photolysis quantum yields.…”

“…An example of these data for 1 day during the campaign, June 19, is reported in the previous publication. 7 Figure 1 shows how the composition changes in the chamber throughout an experiment. The top panel shows an IR spectrum recorded when the canopy is opened, and the middle and lower panels show spectra recorded at later times in the day.…”