We have used a photochemical box model to investigate the effect of temperature-dependent quantum yields of acetone on the chemistry in the upper troposphere. The T-dependent quantum yields produce a photolysis (J) rate up to factor 3--10 slower than room temperature values. This reduced J rate significantly reduces the contribution of acetone to the mid-latitude and tropical UT HOx budgets by factors of 4 and 2 respectively, when constrained with location-specific aircraft observations. The calculated lifetime of acetone in the UT increases from ~75 to ~250 days at mid-latitudes and from ~10 to ~20 days in the tropics, for the conditions used here. This will significantly affect studies aimed at balancing the atmospheric acetone budget. Overall, these new quantum yields have large implications for our understanding of the role of acetone in the chemistry of the UT.