You are permitted to inspect the current eruption [from Kiluea, Hawaii] from a safe distance. […] On humid days water vapour combines with the sulphurous emanations to produce an acrid mist known as vog.
2012, Joanne N. Feldman, Robert I. Tilling, “Volcanic Eruptions, Hazards, and Mitigation”, in Paul S[tuart] Auerbach, editor, Wilderness Medicine, 6th edition, Philadelphia, Pa.:ElsevierMosby, →ISBN, caption of figure 15.37, page 330.e1:
The ongoing eruption of Kiluea's east rift zone (which began in 1983) has put a huge amount of natural pollutants, including sulfur oxides, into the air. Introduced vegetation, such as Kona coffee plants, can be scorched, and downwind of Kiluea, only native species, tolerant of the natural acid rain, survive. The two images compare atmospheric clarity between a volcanic-smog (vog)-free day (A) and a heavy-vog day (B).
2013, Karen Anderson et al., Fodor’s 2014 Hawaii, New York, N.Y.:Fodor's Travel, →ISBN:
On the Islands, fog is a rare occurrence, but there can often be "vog," an airborne haze of gases released from volcanic vents on the Big Island. During certain weather conditions such as "Kona winds," the vog can settle over the Islands and wreak havoc with respiratory and other health conditions, especially asthma or emphysema.