tokens: of the solar wind at 1au is a few km s −1 ( Němeček et al. 2020 ), which is small compared to the average radial wind speed of 400–600 km s −1 . Despite this, attempts to constrain the solar wind AM flux have been made in the past (e.g. Lazarus Goldstein 1971 ; Pizzo et al. 1983 ; Marsch Richter 1984 ; Finley et al. 2019 ). Though each of these studies suffered from uncertainty, either due to the precision of the spacecraft pointing or the ability of the plasma instruments to detect the small tangential flows. These uncertainties are lessened with Parker Solar Probe (PSP) which samples the solar wind within 0.25 au, where the signal to noise on the tangential wind speed measurements should be increased and the influence of wind-stream interactions reduced. However, during its first few encounters, PSP detected tangential solar wind speeds of up to ~ 50 km s −1 ( Kasper et al. 2019 ). These speeds are far greater than expected from magnetohydrodynamic (MHD) modelling (e.g. Réville et al. 2020 ) and, if they were prevalent throughout the corona, would be incompatible with the AM-loss rate implied by the slope of the rotation-age relation. Finley et al. (2020) analyse the data from the first two orbits of PSP and show these flows to be localised, existing along with wind streams that have large negative tangential speeds. Therefore, the average equatorial solar wind AM flux measured by PSP is similar to observationsfrom previous spacecraft. At present, the mechanism(s) that generate these large tangential solar wind speedshave yet to be determined. One possibility is the motion or circulation of open magnetic flux at the base of the wind ( Crooker et al. 2010 ; Fisk Kasper 2020 ; Macneil et al. 2020 ), though this is also not well understood. During PSP’s first two perihelion passes (E01 and E02, respectively), neither the Solar Probe Cup (SPC, Case et al. 2020 ) or the Solar Probe ANalysers (SPAN; Whittlesey et al. 2020 ; Livi et al. 2020 ) were able to confidently measure the properties of the alpha particles in the solar wind. Previously, Pizzo et al. (1983) used Helios observations to show that the alpha particles contain a large negative contribution to the total AM flux (see also Marsch Richter 1984 ). Though, due to an error in spacecraft pointing, the data from Helios required a significant correction, and more recent measurements of the alpha particle AM flux using the Wind spacecraft at 1au instead suggest a much smaller (but still negative) contribution ( Finley et al. 2019 ). As the alpha particles carry roughly 15− 40% of the linear momentum in the solar wind, it is vital that their contribution to the total solar wind AM flux is better understood in order to further constrain the slope of the rotation-age relation for Sun-like stars. In this work, we analyse more recent SPAN-Ion observations from the third and fourth encounters of PSP (hereafter E03 and E04), which we use to determine the mechanical AM flux of both the solar wind
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