Size-resolved particle emission indices in the stratospheric plume of an Athena II rocket

Simultaneous measurements of carbon dioxide (CO₂) mixing ratio and alumina (Al₂O₃) particle abundances between 0.004 and 1.2 μm were obtained in the stratospheric plume wake of an Athena II solid-fueled rocket motor (SRM). A multimode model of the particle size distribution is used to determine the number (N) and surface area (SA) emission indices as 8.7 ± 2.0 × 10¹⁵ per kg and 6.9 ± 2.1 × 10¹⁴ μm² per kg, respectively. Integration of the size distribution shows that 37% of the total SA and 8% of the total mass (M) are contained in the submicron size range (diameter < 1 μm) that most influences the stratospheric impact of alumina particles emitted by SRMs. These values are significantly greater than reported by most previous studies and they imply that the annual global ozone loss associated with SRM alumina emissions is about half of the ozone loss from SRM chlorine emissions alone. Comparison of our results to previous studies raises the possibility that submicron M and SA fraction, and therefore global ozone loss, are inversely related to SRM thrust.