## 2 Research Area  
Australia has regular bushfires throughout mid-to-late summer, and often earlier in the season. Depending on global meteorological conditions, some seasons are worse than others. A particularly bad season was the summer of 2019-2020. Devastating bushfires spread through parts of New South Wales, Victoria and South Australia during the months of December 2019 to February 2020. The 2019/2020 bushfire season was devastating and destructive, releasing millions of tonnes of CO\({}_{2}\), and creating much damage to the environment, property, wildlife, flora and fauna. These recent 2019-2020 'Black Summer' bushfires altogether put a serious burden on health systems, resulting in the loss of a considerable number of lives; 34 in total as well as around 3500 hospitalizations estimated [13] nationwide. A devastating effect on the environment and economy was also recorded [14] and millions of tonnes of CO\({}_{2}\) were released [2] as a result of these fires. Climate change [8; 15; 16] predictions anticipate increases both in the number and intensity of bushfires in the future. Specifically in relation to Australia consider the left panel of Figure 1 which shows constant and relatively low aerosol optical thickness levels over the month of April in 2019 when there were no bushfires in Australia. The right panel depicts the aerosol optical thickness throughout December 2020 during the Black Summer bushfires. It shows high aerosol optical thickness levels which are localized to the south-east of Victoria and New South Wales where the majority of fires occurred. Figure 1 suggests that there is a relationship between bushfires and aerosols. Evidence substantiating these claims in the IPCC report concerning this increased intensity and its consequences are presented in several papers. They show that the smoke released from bushfires during Australia's Black Summer (2019-2020) could lead to persistent stratospheric warming [15], and this could result in large disturbances in the composition of the stratosphere [17], and serve as a potential predictor of the consequences of future extreme bushfire events [16]. This study aims to undertake a statistical analysis using two different tree-based techniques from geospatial statistics of bushfire and stratospheric ozone layer data to discover and measure correlations, both geographically and over time, between these datasets. The specific tree-based method that is used for this analysis will be random forests for spatial-temporal data. We shall also model changing states over the 181-day period covering September to February of ozone with respect to aerosol using Hidden Markov models [18], where the variables analyzed are total sum ozone (TSO) and total sum aerosol (TSA) which are defined in Section 3.1 on data. Our aim is that implementing these methodologies will help establish whether and how ozone levels at high altitudes are affected by bushfires. It is expected that the distributional properties of the total cumulative sum of ozone/aerosol values contained within a localized region must change over time. It is unlikely that on days without bushfires, there will be a rise in local aerosol but on days with bushfire, it is highly probable to observe a rise in local aerosol. The studies cited above, [15; 19; 20], have established a relationship between aerosol and ozone; thus, changes in aerosol levels would also result in changes in ozone but not necessarily in the same locality and possibly with a time delay. Several papers [15; 21] examine the connections between specific bushfires (2017 western Canadian wildfires and the Australian 2019-2020 Black Summer bushfires) and the subsequent depletion of ozone levels in the vicinities of the Antarctic and Arctic. These papers, however, _do not localize the effect bushfires have on the ozone levels_.