However, the oxidation reaction in either acetonitrile or water droplets is expected to occur primarily at the droplet surface, where reactive oxygen species are more prevalent. The rapid evaporation of acetonitrile results in a substantial increase in the surface-to-volume ratio of acetonitrile microdroplets at elevated nebulizing gas pressures (>130 psi), promoting oxidation reactions at the expense of DA reactions at the interface. This hypothesis is supported by studies investigating the impact of varying spray solution flow rates on the reactions (Figure ). Ramping up the flow rate of the spray solution leads to larger microdroplets with a decreased surface-to-volume ratio (Figure ). As both DA and oxidation reactions are expected to occur at the surface of water microdroplets, the efficacy of both these reactions decreased with the increase in the aqueous solution flow rate. However, the DA reaction experienced a more pronounced decrease than the oxidation reaction, reducing the fractional abundance of DA products with an increasing flow rate (Figure ). This result again points to the effect of polar water on enhancing the local concentration of hydrophobic reagents at the air-water interface to impart the DA reaction, albeit with a lower propensity compared to the dominant oxidation reactions. In contrast, the impact of the acetonitrile flow rate on the DA reaction was different, i.e., the fractional abundance of DA products increased by increasing the flow rate (Figure ). This result indicates that the DA reaction in acetonitrile microdroplets is not restricted solely to its surface but predominantly extends throughout its core. The increased solution mass flow supplied a greater quantity of reagents per droplet, and due to the rapid evaporation of acetonitrile, the droplet became enriched with reagents confined in a small space, which subsequently impacted the DA reaction inside the acetonitrile droplet.