Outer islands: Oʻahu, Maui, Kauaʻi, Molokaʻi, Lānaʻi, Niʻihau, Kahoʻolawe.
On the Big Island, the primary irritants in vog are sulfur dioxide (SO2) and tiny sulfuric acid (H2SO4) droplets called aerosols. But as the wind carries the vog far away from Kīlauea volcano, the SO2 begins to react with oxygen and moisture in the air to form additional sulfuric acid aerosol particles.
As more time passes, this acidic vog gradually reacts with small amounts of ammonia that are present in the atmosphere. (This ammonia is naturally produced by biological decay in moist tropical soils.) Ammonia, when dissolved in water, is basic, forming NH4OH—the active product in household ammonia—and reacts with the sulfuric acid aerosols to form ammonium sulfate. By the time the Big Island’s vog plume visits the neighbor islands, the sulfur dioxide and sulfuric acid have already been converted almost entirely to ammonium sulfate [(NH4)2SO4]. Even though ammonium sulfate particles aren’t acidic, they still can irritate the eyes and throat and can trigger an asthmatic response in sensitive individuals.
Fortunately for residents of the small islands, when the vog comes to visit, it is possible to reduce the concentration of ammonium sulfate in your home. Ammonium sulfate is very soluble in water. All you have to do is drape a wet cheesecloth, or a wet towel, over a box fan in your living room. The fan will draw the air from your living room through the wet cloth, depositing the ammonium sulfate on the towel, where it will immediately dissolve, leaving your air much cleaner. If you have an air conditioner or dehumidifier, these will also help, although at a higher energy cost, by dissolving the ammonium sulfate particles in moisture formed on their condenser coils.