In this thesis, we assess various climatic impacts of stratospheric aerosol injection (SAI), a geoengineering proposal that aims to cool Earth by enhancing the sunlight-reflecting aerosol layer in the lower stratosphere. To this end, we employ simpleradiative transfer models, a detailed radiative transfer code (SOCRATES), and two Hadley Centre general circulation models (HadGEM2-CCS and HadGEM2-ES). We find that the use of a light-absorbing aerosol (black carbon) for SAI would result in significant stratospheric warming and an unprecedented weakening of the hydrological cycle. Conversely, we find that SAI with sulphate or titania aerosol could counteract many of the extreme climate changes exhibited by a business-as-usual scenario (RCP8.5) by the end of this century. In a separate investigation, we show that volcanic aerosol dispersion following low-altitude volcanic eruptions can exhibit high sensitivity to the ambient weather state. Volcanic aerosol may get 'trapped' in a single hemisphere or transported to the opposite hemisphere depending simply on the meteorological conditions on the day of the eruption. In a final study, we investigate the impacts of SAI on North Atlantic tropical storm frequency. We find that SAI exclusively promoted in the southern hemisphere would increase North Atlantic storm frequency, and vice versa for northern hemisphere SAI. The results of this thesis should promote further research into SAI, which could conceivably be deployed to maintain global-mean temperature below the COP21 target of +1.5 K above pre-industrial levels, whilst society transitions onto a sustainable energy pathway. Conversely, the possibility of SAI being weaponised, for instance, to specifically increase North Atlantic tropical storm frequency, should motivate policymakers to implement effective regulation and governance to deter unilateral SAI deployments.

This paper aims to study how varying crossflow burning temperatures from 1100 C to 1800 C affect the liquid droplet breakup, size distribution, and atomization of a liquid water jet injected into a vitiated crossflow. The LJIC injection mechanism was implemented using the high-pressure axially staged combustion facility at the University of Central Florida. The measurement devices used to gather particle data from the exhaust plume were the TSI Aerodynamic Particle Sizer (APS), which measures particles between 0.523 µm and 20 µm, and the Sensirion SPS30 (SPS30), which measures particles between 0.3 µm and 10 µm. Both measurement devices were placed 3 ft away from the choked exit. Table 3 shows that the 1800 C crossflow temperature behaved as predicted by having the largest particle distribution of 67.97% and the largest particle count of 19,301 at 0.523 µm. The 1100 C crossflow produced the second-largest normalized particle count of 66.69% and raw particle count of 20,209 at 0.523 µm. This result is contrary to the original hypothesis because it shows that the relationship between temperature and particle count is non-linear and that many other factors must be at play in the atomization process, such as the droplet distribution at the nano level. The SPS30 was used to compare the particle size distributions between a 1500 C and 1800 C crossflow. Acquiring number concentration data for particles up to 10 µm in size, the 1800 C crossflow had a distribution peak at 802.76416 N/cm3, and the 1500 C crossflow had a peak of 867.28272 N/cm3. For the 0.5 µm peak, The 1800 C had a 10 µm particle size distribution peak at 674.27.76416 N/cm3, and the 1500C crossflow had a peak of 730.501 N/cm3. The decreased number concentration from 1500 C to 1800 C case grants the water particles in the 1800 C crossflow increased surface area, which allows for increased heat exposure from the vitiated crossflow [7]. Despite some nonlinear particle count results, the highest crossflow temperature of 1800 C produces the best atomization results by reducing the total particle count and having the largest collection of particles at the lowest detectable particle size of 0.523 µm.