As mentioned in the previous post, it is important to note the kind of propellants and therefore the type of emissions and which part of the atmosphere pollutants are released. One of the most common and studied propellants are solid rocket motors (SRMs) which are used for lift offs of shuttles and missions like the USA’s Titan and Delta launches (Dallas et al., 2020). The main concern with SRMs are the emissions of HCl, alumina, and soot which contribute either to stratospheric ozone depletion or climate forcing, or both.
As SRM-propelled rockets pass through the atmosphere, the plumes of smoke release compounds that interact with other atmospheric elements. On top of the effect of chlorine radicals as mentioned in the previous post, Jackman (1996) also found that alumina particles (Al2O3) further contribute to ozone depletion by behaving very similarly to stratospheric surface aerosol. In fact, one-third of ozone depletion from SRM is contributed by alumina with the remaining from HCl. Together, Ross et al. (2000) demonstrated that these particles have can almost completely destroy ozone within a whopping 8 km of a shuttle passing by the stratosphere! Of course, this only occurs within 30 to 60 minutes of launch before conditions subside but the long term implications have not yet been concretely established.
Less directly, there are concerns with the production of soot and alumina that causes radiative forcing. While I hope to delve deeper into carbon emissions in a later post, I hope to outline the mechanism of climate forcing here and expand on other socioeconomic inequalities for the later post. It was initially believed that the whiteness of alumina would have a cooling effect on climate by scattering solar flux but studies have demonstrated that they behaved similarly to soot. Specifically, cooling is minimal as these particles absorb earth’s outgoing longwave radiation (Ross and Sheaffer, 2014). A net warming of the surface and the stratosphere is the result. Worryingly, a recent study suggests that this may further exacerbate ozone depleting by increasing rates of reaction that causes ozone to decompose (Ross and Vedda, 2018). This effectively means that ozone depletion will continue to be an issue as long as we continue shooting rockets out of orbit…
However, there are also other issues closer to the ground when it comes to SRMs. In the next post, I’ll be highlighting some of these abiotic and biotic impacts of launches on the ground (and water). See you then!
References
Dallas, J. A., Raval, S., Gaitan, J. A., Saydam, S., & Dempster, A. G. (2020). The environmental impact of emissions from space launches: A comprehensive review. Journal of Cleaner Production, 255, 120209.
Jackman, C. H., Considine, D. B., & Fleming, E. L. (1996). Space shuttle’s impact on the stratosphere: An update. Journal of Geophysical Research: Atmospheres, 101(D7), 12523-12529.
Ross, M. N., Toohey, D. W., Rawlins, W. T., Richard, E. C., Kelly, K. K., Tuck, A. F., … & Sheldon, W. R. (2000). Observation of stratospheric ozone depletion associated with Delta II rocket emissions. Geophysical research letters, 27(15), 2209-2212.
Ross, M. N., & Sheaffer, P. M. (2014). Radiative forcing caused by rocket engine emissions. Earth’s Future, 2(4), 177-196.
Ross, M. N., & Vedda, J. A. (2018). The policy and science of rocket emissions. Center for Space Policy and Strategy, The Aerospace Corporation.