Vog, sometimes thought as volcanic fog, is the acidic gases spewing out of the volcano and mixing with the atmosphere. There's an assortment of chemical brews in the stuff, but the main component seems to be sulfur dioxide (SO2). As it mixes with the air, it undergoes chemical changes resulting in acidic components (think: sulfuric acid) and reacts with volcanic ash particles resulting in irritating particulates. Rain picks up these chemicals, thus giving areas downwind of the eruption significantly acidic rain. I don't know all the science about vog, but I'm very aware of how it affects us.
How does vog effect humans? First of all, most people say they are not bothered by the vog. But some people are, especially those who already have other medical conditions. Plus it depends upon one's exposure. Some areas have rather persistent vog problems, other areas occasional intermittent problems, yet other areas with very little vog at all. Depending upon the wind, vog can come and go, be there for 15 minutes then be gone. How close you are to the eruption dictates the type and strength of vog. So Volcano, when the wind is right, can have horrendous vog which drives everybody indoors. But usually they have no vog problems because the wind normally blows vog away from the town. Pahala, Wood Valley, and upper Oceanview experience vog fairly regularly because of the prevailing winds. People living in those areas seem to report the most health problems. On bad vog days, vog can cause: headache, eye irritation, sore throat, sinus and nasal irritation, sore or cracked lips, breathing difficulties & shortness of breathe, increased heart rate, aches and pains, lack of energy and stamina, disrupted sleep, bizarre dreams, and flare ups of existing medical conditions (people notice that skin problems get worse, otitis flares up, more clogged sinuses, and just about any condition that involves inflammation seems to get worse).
How about me and hubby? Vog doesn't seem to bother me severely. First of all, we don't get much heavy exposure where we are. But when I do, I often get the slightly cracked lips, sore eyes, irritated nose, achy joints. Hubby gets all those plus a light headache and becomes short tempered (he doesn't see it though, but take my word for it, he gets irritable).
I haven't noticed any significant problems with our own animals. Ranchers over in Pahala report eye irritation in the cattle, plus some wonder if the skin and abortion problems are vog related. Luckily our homestead gets little chronic vog, so the livestock are spared the vog problems.
Our farm cab suffer from three direct vog issues : burned vegetation; soil changes; damage to anything metal. On a really bad vog day, which only happens once or twice a year, sensitive plants will have foliar burns. Lettuce and taro are the top plants to be affected on my place. The burned leaf parts lose color and by the next day, turn brown and die. Farms closer to the volcano or those which get persistent vog report problems with many other different crops.
Soil changes appear to be the result of acid rain. The soil pH bounces all over the place depending upon weather conditions. So I need to monitor the soil pH frequently. The vegetable garden requires pH within a certain range for the veggies to be productive in my system, so I tend to adjust the pH as needed. Plus I have to check the pH of my catchment water. If allowed to get too acidic, it could damage my tanks, pumps, and piping.
The acid rain and vog (it does not need to be raining for damage to occur) severely damage anything metal. Field fences rust away in a few years, tools rust even when stored indoors, any metal parts disintegrate, the screw heads holding metal rooves in place rust away, even the lids on my mason jars rust on my pantry shelves. Brake rotors on vehicles pit, resulting in frequent brake jobs.
So is vog everywhere? Yes and no. As I said, some areas have worse vog issues than others. A lot depends upon the wind conditions. But the terrain also has a bearing. Air tends to pocket in Wood Valley and Captain Cook, so those areas are noted for bad vog. Air also tends to swirl toward and stagnate in the Kona area, so even though it is far from the eruption, Kona experiences foggy air far worse than our homestead farm. A half mile up the mountain from our farm, vog is almost constantly present. But our farm experiences very little vog. So the change in terrain makes a big difference. Down at my seed farm, there is seldom any vog at all. Amazing how things can be so different when only a mile, or even 1/2 mile apart.