Global stratospheric effects of the alumina emissions by solid-fueled rocket motors

We simulate accumulation of Al2O3 particles in the atmosphere produced by s olid-fueled rocket motors by using the Goddard Institute for Space Studies/ University of California at Irvine three-dimensional (3-D) chemistry-transp ort model (CTM). Our study differs from Jackman et al. (1998) by applying a 3-D CTM, considering 13 size bins for the emitted particles from 0.025 to 10 mum and taking into account their washout, gravitational sedimentation, and coagulation with background sulfate aerosol. We assume an initial trimo dal size distribution of Al2O3 particles (Beiting, 1997) with 2.8% by mass of the alumina emitted as particles with radius of less than 1 mum. Our tes t case adopts a stratospheric source of 1120 tons/yr equivalent to nine spa ce Shuttle and four Titan IV launches annually. The calculated steady state surface area density (SAD) and mass density for the scenarios with sedimen tation of alumina particles have maximum values in the lower stratosphere i n the Northern Hemisphere of up to 7x10(-4) mum(2)/cm(3) and 0.09 ng/m(3), respectively, or about 1000 times smaller than those of the background sulf ate aerosol. Our results are sensitive to the emitted mass fractionation of alumina (EMFA) showing the values for the SAD or mass density higher or lo wer by an order of magnitude owing to a poorly known EMFA. Chemical implica tions of alumina particle accumulation for the ozone balance are estimated by using the Atmospheric and Environmental Research 2-D model assuming chlo rine activation on Al2O3 surfaces via the ClONO2 + HCl --> Cl-2 + HNO3 reac tion with a probability of 0.02 (Molina et al., 1997). Owing to the very sm all Al2O3 SAD, any additional ozone depletion due to Al2O3 emissions is als o small (0.0028% on a global annually averaged basis for the scenario with sedimentation, or about 4 times smaller than the ozone response to chlorine emissions only). The ozone depletion potential of the alumina emissions is about 0.03-0.08 for the scenarios using the EMFA of Beiting (1997) and lar ger by an order of magnitude for the EMFA of Brady and Martin (1995).