Potential climate impact of black carbon emitted by rockets

Abstract

A new type of hydrocarbon rocket engine is expected to power a fleet of suborbital rockets for commercial and scientific purposes in coming decades. A global climate model predicts that emissions from a fleet of 1000 launches per year of suborbital rockets would create a persistent layer of black carbon particles in the northern stratosphere that could cause potentially significant changes in the global atmospheric circulation and distributions of ozone and temperature. Tropical stratospheric ozone abundances are predicted to change as much as 1%, while polar ozone changes by up to 6%. Polar surface temperatures change as much as one degree K regionally with significant impacts on polar sea ice fractions. After one decade of continuous launches, globally averaged radiative forcing from the black carbon would exceed the forcing from the emitted CO2 by a factor of about 105 and would be comparable to the radiative forcing estimated from current subsonic aviation.

Radiative forcing caused by rocket engine emissions

“…The factor of 2/3 accounts for typical launches where about two thirds of a rocket's total propellant burn (all stages, to orbit) takes place above the tropopause. Previous global models [Jackman et al, 1998;Danilin et al, 2001;Ross et al, 2010] suggest that midlatitude launches generate a zonally symmetric accumulation region between about 15 and 30 km altitude and 30 ∘ N-80 ∘ N latitude, illustrated in Figure 2. Equatorial launch emissions (accounting for ∼20% of all launches) will be entrained in the vertical flow at low latitudes and will possibly add proportionally less to the accumulation region than the midlatitude launches.…”

“…We do not consider atmospheric features that evolve in response to the change in radiative flux in the accumulation layer, which may be significant, essentially restating that we use instantaneous RF in order to keep that point clear. Ross et al [2010] showed how modest localized BC heating in the rocket accumulation layer can modify the global circulation; changes in the global ozone distribution were significant in that work as the atmosphere returned to thermal equilibrium.…”

“…On theoretical grounds, we expect hybrid engines to have EI(BC) larger than kerosene engines. While currently contributing nearly zero to global emissions, the hybrid remains of interest because published plans (Virgin Galactic, 2014, www.virgingalactic.com) suggesting very aggressive growth of this rocket type can be expected in the future so that, despite the small propellant burn per launch, the launch rate may at some future time be large enough to become a significant RF source [Ross et al, 2010]. For hybrid EI(BC) we assume a possible range between 20 and 60 g kg −1 and a preferred value for calculation of 40 g kg −1 .…”

“…SRM particles are more difficult to assess in this regard, as we saw in section 3. BC or submicron alumina particles (that we define as the alumina SMF) emitted into the stratosphere will reach a quasi steady state in the accumulation layer (Figure 2) [Ross et al, 2010;D01].…”

“…In addition, the rocket industry has no international cooperative organization equivalent to the International Civil Aviation Organization that serves as an information, guideline, and regulatory apparatus for aircraft. Ross et al [2010] demonstrated the significant potential rockets have to alter regional RF as well as the global circulation, should certain types of space transportation grow as planned. In this context, it is perplexing that detailed models of supersonic transport emissions continue to appear in the literature [e.g., Grewe et al, 2007] when such vehicles are not likely to appear soon whereas space transportation is a growing actuality.…”