Low-temperature combustion (LTC) represents a promising technology being deployed in emerging advanced compression ignition (ACI) engines. These engines have the potential to reach higher thermal efficiencies and substantially reduce NOx and particulate soot (i.e., elemental carbon) emissions. For certain hydrocarbon fuels, LTC is dominated by chain-branching reactions involving peroxy radicals (RO2) within the 500K – 700K temperature range. This reaction sequence aligns with a phase referred to as low-temperature heat release (LTHR) or 'cool flame', causing the fuel to display two-stage ignition characteristics. This distinctive behavior plays a vital role in defining autoignition timing and, consequently, the comprehensive performance of ACI engines. This dissertation presents our findings on the formation of 'first-stage organic aerosols (OA)' that occur within the same temperature range as LTHR. We demonstrate, through a series of online and offline measurements, that first-stage OA have fundamentally different formation pathways than what is traditionally recognized for second-stage OA, or incipient soot, that forms at relatively higher temperatures (>1000K). We further established that first-stage OA is comprised of highly oxygenated compounds we refer to as oxygenated primary organic aerosols (OxyPOA), which retains chemical properties similar to those of secondary organic aerosols (SOA). We also provide evidence of OxyPOA in emissions from spark-ignition and ACI engines, illustrating the relevance of elucidating OxyPOA formation to understanding OA pollution in current and future urban atmospheres. Motivated by the necessity of fuel additives in ACI engines that inhibit radical formation to reduce LTHR and enhance autoignition timing, we extended our investigation to include three additives with differing inhibitory capacities. We mixed each additive with a two-stage ignition fuel, to investigate their effects on the formation of first-stage OA. The results demonstrated that additives with a stronger inhibitory nature were more successful in suppressing first-stage OA formation. Furthermore, each additive displayed unique influences on the chemical makeup of the resulting first-stage OA.