The
adsorption of gas-phase pyruvic acid (CH3COCOOH)
on hydroxylated silica particles has been investigated at 296 K using
transmission Fourier transform infrared (FTIR) spectroscopy and theoretical
simulations. Under dry conditions (<1% relative humidity, RH),
both the trans–cis (Tc) and trans–trans (Tt) pyruvic
acid conformers are observed on the surface as well as the (hydrogen
bonded) pyruvic acid dimer. The detailed surface interactions were
further understood through ab initio molecular dynamics simulations.
Under higher relative humidity conditions (above 10% RH), adsorbed
water competes for surface adsorption sites. Adsorbed water is also
observed to change the relative populations of the different adsorbed
pyruvic acid configurations. Overall, this study provides valuable
insights into the interaction of pyruvic acid with hydroxylated silica
surfaces on the molecular level from both experimental and theoretical
analyses. Furthermore, these results highlight the importance of the
environment (relative humidity and coadsorbed water) in the adsorption,
partitioning, and configurations of pyruvic acid at the surface.
The
surface chemistry and photochemistry of gas-phase pyruvic acid
(CH3COCOOH) on two oxides, Al2O3 and
TiO2, have been investigated using transmission Fourier
transform infrared spectroscopy and mass spectrometry. At 298 K, the
carboxylic acid group within pyruvic acid is found to react with surface
hydroxyl groups (M–OH, M = Al, Ti) to yield pyruvate as a predominant
adsorbed organic species. Upon broad-band UV irradiation (λ
> 280 nm), there is a loss of adsorbed pyruvate with the concomitant
formation of new products. The photochemical loss of pyruvate is higher
on TiO2 than on Al2O3 indicating
that the photochemistry is enhanced on the surface of a semiconductor
oxide, TiO2, compared with an insulator oxide, Al2O3. Analysis of products extracted from the surface with
mass spectrometry shows the formation of several new compounds. This
includes zymonic acid, which is found to be present under both dark
and light conditions, and other higher-molar-mass oligomeric species
such as parapyruvic acid, acetolactic acid, and 2,4-dihydroxy-2-methyl-5-oxohexanoic
acid that form only under irradiation. Although this study shows that
there are some parallels between the aqueous-phase photochemistry
of pyruvic acid and the photochemistry of adsorbed pyruvic acid in
terms of the products that form, there are also distinct differences,
with several other new photoproducts observed on these oxide surfaces,
including lactic acid dimers and trimers as well as significant amounts
of even larger oligomeric species not seen in the aqueous phase. Because
of the role of pyruvic acid, the simplest of the α-keto acids,
in the atmosphere and in metabolic pathways, these results have implications
for the chemistry that occurs in both indoor and outdoor environments
and under prebiotic Earth conditions. Overall, this study provides
insights into the surface chemistry and photochemistry of pyruvic
acid on different oxides (Al2O3 and TiO2).
Measurements of the photodissociation constant for nitrous acid (jHONO) were made at an urban site in Toronto, Canada, during the months of May-July 2005, using an optically thin actinometer. Operating details of the jHONO monitor are reported, along with laboratory tests. Measurements of jHONO were obtained for solar zenith angles ranging from 20-75 0 , under clear and cloudy skies. Maximum error estimates on jHONO under clear skies range from 11 % at sunrise, to 4% at solar noon, with a minimum detection limit of 5.7 x 10-4 /sec for our actinometer. Measured clear-sky values of jHONO were compared with values calculated by a four-stream discrete ordinate radiative transfer (RT) model (ACD TUV version 4.1), and were found to be within better than 10% agreement for solar zenith angles <65 0 • For conditions of scattered cloud, enhancement and suppression of the jHONO values occurred by as much as 16%-70%, and 59%-80%, respectively. The integrated band area of the mr* transition for gas-phase nitrous acid yields an oscillator strength, f = (1.06 ± 0.044) x 10-3 (based on clear-sky data), 19.1 % higher than the value reported by Bongartz et al. (1991).
The original version of this article unfortunately contains mistakes introduced during the production process. The corrections are given in the following list:(1) Equation (18) (immediately following (17) was incorrect. The formula already given in (29) has been substituted for the correct equation (18). The correct equation (18) is now shown correctly in the article. (2) In all occurrences of the subscripts, greek symbols were missing. For example, the best fit reaction probability (ɣ best-fit ) appeared as just best-fit (in subscript), without the gamma. The article is now corrected showing the missing greek symbols with the subscripts.The original article was corrected.
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