The short answer is, it depends on what “limit” means. 
All have “sinned and come short of the glory of God”(Rom. 3:23)

The consequence of Adam’s sin is “eternal death” or “second death” from which there is no resurrection. There is a “first death” because of our mortal flesh nature, from which all were “appointed to die” then be resurrected(Heb.9:27)
And, because of that, salvation is needed from this particular eternal death. But, salvation is a process strategically planned before creation. And, atonement is first and foremost. It refers to mankind’s reconciliation to God the Father. This requires the “atoning blood” from a “Passover Lamb” chosen from the “foundation of the world”. Remember, “without shedding of blood, there is no remission of sins” (Heb.9:22)
Since this atonement is for all mankind, (as Adam sinned so all were counted to have sinned), it is therefore “unlimited” as to its encompassing depth and breadth. . Meaning, for all and not limited to any particular person. 
However, , this atonement, is limited as to the time of its availability and effectiveness. It is limited first to those belonging to the “firstfruits” who will manifest themselves in the “first resurrection”. Then will be available and effective to those who will participate in the “second resurrection” occurring after the “Millenium”. Those who will be in the “second resurrection” and will not accept Christ and refuse the Holy Spirit’s in-dwelling will be judged to suffer “damnation and second death in the lake of fire”(Gehenna fire). 
In summary, atonement is unlimited as it encompasses all mankind. But, it is limited to certain people at a particular period of time.