This question is intriguing because all seven angels were instructed to pour out their bowls “on the earth” (Revelation 16:1). The term “earth” can refer to man’s dwelling as opposed to “heaven,” God’s dwelling (Genesis 1:1; Psalm 115:16). In this understanding, “earth” is the part of his creation that God has entrusted to mankind with the command to have dominion over it (Genesis 1:26, Genesis 1:28). The term “earth” can also refer to (what we would call) “land” as opposed to “sea” (Revelation 13:11 in contrast to Revelation 13:1). The seven angels of Revelation 16:1 must all pour out their bowls “on the earth” in the broad sense of Genesis 1:1 and Genesis 1:26 (including sea, rivers, sky), and the first angel obeyed that command by pouring his bowl more narrowly on land (as opposed to sea). His ashes (= wrath) fall, then, on where people actually live (on land) and so where people are. So it is no surprise that people feel in direct fashion the result of God’s wrath, namely, sores.
2 So the first angel went and poured out his bowl on the earth, and harmful and painful sores came upon the people who bore the mark of the beast and worshiped its image.