67P, identifying a source at ϕ = 40◦N. This latitude is approximately 40◦south of the active region proposed in our study, a discrepancy we attribute to our limited sensitivity to mirrored fans, which reduced the precision of latitude conversions. Despite this limitation, our Fan A and NH2 structure align well with the eastern component of the mirrored fan described in Boehnhardt et al. (2024), possibly indicating a shared activity source for dust particles and NH2 around ϕ = 40◦N. Further correlations can 38 be drawn to in-situ findings by Biver et al.

(2019), which identified the majority of gas sublimation originated from high northern latitudes during the pre-perihelion period (July 2014 to February 2015), including contribution from parent species NH3. In-situ pre-perihelion results from L¨auter et al. (2022) show prolonged northern emission of NH3 between 0-40◦N latitudes, consistent with this work and previous studies. Finally, the global distribution of NH3 activity by mass fraction is nearly uniform (around 0.3%) L¨auter et al. (2022). This implies that NH2 signal should be relatively uniform from north to south, however, we observe the opposite in our maps where the NE quadrant is 10-15% more intense than the rest of the coma, suggesting additional sequestered sources of NH2 in the north. While photochemical scale lengths for this region are enhanced by 1.5-1.9× the average fitted values for the rest of the coma, it is most likely the northern pre-perihelion NH2 signal is coming from a mix of both nucleic NH3 sublimation and possible extended source fragmentation. One possible interpretation for an extended source of NH2 could be ammonium salts (NH+ 4 X−), including ammonium formate and ammonium sulfate in 67P’s highly porous refractory dust, initially identified by VIRTIS (Poch et al., 2020) and ROSINA instruments (Altwegg et al., 2020). Evidence from Rosetta’s COSIMA instrument indicates that 67P’s dust is composed of nearly equal amounts of high molecular weight organics and anhydrous mineral phases (45-55% wt), with up to 90% porosity (Fray et al., 2016;
Langevin et al., 2017), which could provide a mechanism to preserve NH+ 3 X−
further from the nucleus. G¨uttler et al. (2019) revealed that solid, fluffy, and porous dust particles undergo complex fragmentation and fading processes as they move outward from the nucleus, ultimately depositing any hidden volatiles into the coma. In this context, we argue that the northern pre-perihelion NH2 signal could partially result from fragmentation and sublimation of porous, organic-rich dust particles that could release semi-volatile species like ammoniated salts along their trajectories, which further dissociate into NH2 upon exposure to solar radiation (Altwegg et al., 2020; Poch et al., 2020). One trend in our maps is the detection of CN signal solely from the southern hemisphere of 67P. Opitom et al. (2017) first reported the emergence of southern CN signal after the vernal equinox, likely caused by the change of season and migration of the subsolar point to the southern hemisphere of 67P. Similarly, observations by Knight et al. (2017) from 2015 report broad CN fans from the southern hemisphere, which further confirmed this trend. This 39 change in seasons illuminated long-dormant (5.5 yr)