Abstract
The pressure dependence of the relative photolysis rates of HCHO and HCDO has
been investigated using a new photochemical reactor at the University of Copenhagen.
The relative photolysis rate of HCHO vs. HCDO under UVA lamp irradiation was mea-
5 sured at total pressures of 50, 200, 400, 600 and 1030 mbar. The relative dissociation
rate kHCHO/kHCDO was found to depend strongly on pressure, varying from 1.1±0.1 at
50 mbar to 1.75±0.10 at 1030 mbar. The products of formaldehyde photodissociation
are either H2+CO (molecular channel) or HCO+H (radical channel). The partitioning
between the channels has been estimated using available values for the absorption
10 cross section and quantum yield. As a result of the change in pressure with altitude
the isotope effect for production of molecular hydrogen is found to change from a value
of kH/kD=1.8±0.2 at the surface to unity at 50 km. The relative importance of the two
product channels changes with altitude as a result of changes in both pressure and
actinic flux. The study concludes that the D of photochemical hydrogen produced in
15 situ will increase substantially with altitude.
been investigated using a new photochemical reactor at the University of Copenhagen.
The relative photolysis rate of HCHO vs. HCDO under UVA lamp irradiation was mea-
5 sured at total pressures of 50, 200, 400, 600 and 1030 mbar. The relative dissociation
rate kHCHO/kHCDO was found to depend strongly on pressure, varying from 1.1±0.1 at
50 mbar to 1.75±0.10 at 1030 mbar. The products of formaldehyde photodissociation
are either H2+CO (molecular channel) or HCO+H (radical channel). The partitioning
between the channels has been estimated using available values for the absorption
10 cross section and quantum yield. As a result of the change in pressure with altitude
the isotope effect for production of molecular hydrogen is found to change from a value
of kH/kD=1.8±0.2 at the surface to unity at 50 km. The relative importance of the two
product channels changes with altitude as a result of changes in both pressure and
actinic flux. The study concludes that the D of photochemical hydrogen produced in
15 situ will increase substantially with altitude.
| Original language | English |
|---|---|
| Journal | Atmospheric Chemistry and Physics Discussions |
| Volume | 9 |
| Pages (from-to) | 24029–24050 |
| Number of pages | 21 |
| ISSN | 1680-7367 |
| Publication status | Published - 12 Nov 2009 |