Volcanic smog, also known as vog, is a type of air pollution that forms when sulfur dioxide gas and other pollutants emitted from volcanic activity interact chemically with atmospheric moisture, oxygen, dust, and sunlight. The resulting mixture is a hazy combination of sulfur dioxide gas and aerosols, primarily sulfuric acid and other sulfate compounds. Vog can irritate the lungs and make existing lung problems worse, and it poses a health hazard by aggravating preexisting respiratory ailments. When atmospheric moisture is abundant, sulfuric acid dioxide gas in vog combines with it and falls as acid rain.

Volcanoes release plumes of ash, dust, sulfur dioxide, carbon monoxide, and other harmful gases into the air, with sulfur dioxide being the most harmful of these gases. When the gases react with oxygen, moisture, and sunlight in the atmosphere, volcanic smog forms. Vog can affect how well your lungs work and may also affect your immune system. The acidic particles in vog can worsen lung conditions such as asthma, bronchitis, chronic obstructive pulmonary disease (COPD), emphysema, and any other long-term (chronic) lung condition. Symptoms of vog exposure include breathing problems, shortness of breath, coughing, flu-like symptoms, headaches, lack of energy, more mucus production, sore throat, and watery, irritated eyes.

To protect yourself from vog, it is recommended to limit outdoor activities and stay indoors to reduce exposure to vog. If you already have breathing problems, taking steps such as practicing good hygiene, using air filters, and wearing masks can prevent your breathing from getting worse when you are exposed to vog. People who may be particularly sensitive to vog are those with health conditions such as asthma, lung disease, and heart disease, the elderly, pregnant women, and children.