Antonyms of noxious:
harmless, innocuous, innoxious, advantageous, favorable, helpful, profitable, serviceable, beneficent, good, invigorating, rejuvenating, useful, beneficial, healthful, life-giving, salutary, wholesome, hygienic, sanitary, nutritious, healthy, propitious, curative, palliative, remedial, salubrious, secure, sound, benignant, noncorrosive, nondestructive, nonfatal, noninfectious, nonlethal, nonpoisonous, nonpolluting, nontoxic, nonvenomous, anodyne, benign, hurtless, innocent, inoffensive, safe, acceptable, agreeable, alluring, appealing, attractive, blessed, congenial, darling, delectable, delicious, delightful, delightsome, desirable, dreamy, dulcet, enjoyable, felicitous, gratifying, heavenly, inviting, likable, luscious, nice, palatable, pleasant, pleasing, pleasurable, satisfying, savory, sweet, welcome, unexceptionable, unobjectionable, restorative.
Examples of usage:
  1. On opening the door to the main office I met again what I thought was the noxious vapor.
  2. I am aware that the aristocracy of wealth is a noxious weed that spreads its deleterious branches through our cities and large towns but not yet so widely and luxuriant as to prevent merit and genius from acquiring a rapid and healthful growth.
    "Sages and Heroes of the American Revolution", L. Carroll Judson.
  3. There was every danger that the lower level might be so filled with the noxious vapor as to cause an explosion, and both men and boys labored manfully.
    "Down the Slope", James Otis.