A comparison of model calculations and measurements of acetone in the troposphere and stratosphere

We present 1-D eddy diffusion model calculations of the distributions of propane and acetone in the atmosphere for continental conditions. The magnitude of the surface seasonal variation in propane mixing ratios that we obtain is in general agreement with measurements at the surface and in the free troposphere. A comparison of the absolute values of the model with propane measurements suggests that a larger surface flux than we have used may be more appropriate for continental conditions. The acetone model results for summer conditions that we obtain are also in reasonable accord with measurements. However, we find serious disagreement between the model winter profiles of acetone and the measurements at the tropopause and in the lower stratosphere. The measured values are lower than the model values at 45° N by a factor of 7–30. In addition, it is also surprising that, given the relatively long lifetime of acetone, free tropospheric values of acetone more representative of surface values have not been measured. The results simulating the decay of elevated levels of propane in the upper troposphere caused by rapid convective transport of boundary layer air indicate that propane will be primarily dispersed by transport rather than destroyed photochemically. Thus, the impact on acetone and PAN is minimal.     

Quantum yields for the photodissociation of acetone in air and an estimate for the life time of acetone in the lower troposphere

The room-temperature photodecomposition of acetone diluted with synthetic air was studied at nine wavelengths in the spectral region 250–330 nm. The quantum yields for the products CO₂ and CO indicated that it was not possible to suppress secondary reactions sufficiently, even with acetone/air mixing ratios as low as 150 ppmv, to derive from these data primary acetone photodissociation quantum yields. The behavior of CO₂ and CO formation nevertheless provides some insight into the mechanism of acetone photodecomposition. When small amounts of NO₂ are added to acetone/air mixtures, peroxyacetyl nitrate (PAN) is formed. Quantum yields for PAN are reported. They are better suited to represent primary quantum yields for acetone photodissociation, because PAN is a direct indicator for the formation of acetyl radicals. The data were combined with absorption cross-sections for acetone measured at wavelengths up to 360 nm to calculate photodissociation coefficients applicable to the ground-level atmosphere at 40° northern latitude. Comparison with the rates for the reaction of acetone with OH radicals shows that both processes contribute almost equally to the total acetone losses in the lower atmosphere. The resulting atmospheric life time at 40° northern latitude is 32 days, on average. This value must be considered an upper limit, since it does not take into account acetone losses due to the reaction of excited triplet acetone with oxygen.     

Henry's law coefficients for aqueous solutions of acetone,acetaldehyde and acetonitrile,and equilibrium constants for the addition compounds of acetone and acetaldehyde with bisulfite

Vapor phase concentrations of acetone, acetaldehyde and acetonitrile over their aqueous solutions were measured to determine Henry's law partition coefficients for these compounds in the temperature range 5–40 °C. The results are for acetone: ln(H ₁/atm)=–(5286±100)T+(18.4±0.3); acetaldehyde: ln(H ₁/atm)=–(5671±22)/T+(20.4±0.1); and acetonitrile: ln(H ₁/atm)=–(4106±101)/T+(13.8±0.3). Artificial seawater of 3.5% salinity in place of deiionized water raisesH ₁ by about 15%. A similar technique has been used to measure the equilibrium constants for the addition compounds of acetone and acetaldehyde with bisulfite in aqueous solution. The results are ln(K ₁/M ^–1)=(4972±318)/T–(11.2±1.1) and ln(K ₁/M ^–1)=(6240±427)/T–(8.1±1.3), respectively. The results are compared and partly combined with other data in the literature to provide an average representation.