Voggy weather is expected for another day before tradewinds gradually return and usher away the volcanic impurities in the air around the islands, the National Weather Service said Saturday.

“The air quality should begin to improve, if not by (today), by around Monday and definitely by midweek,” said weather service meteorologist Bob Burke. The returning tradewinds will blow the vog away from the smaller islands, but the haze will linger around parts of Hawaii island because it’s closer to the source, Burke said.

The volcanic haze has been around the islands for the past several days because of a stable air mass over the state interfering with the trades. A light southeasterly wind then pushed the vog around the smaller islands.

The stable air mass, or ridge, will move north this week, and the tradewinds will return, first to Hawaii island on Monday and then to the smaller islands by Tuesday or Wednesday.

Vog, short for volcanic fog, refers to the hazy air pollution caused by the emissions from Kilauea, chiefly water vapor, carbon dioxide and sulfur dioxide, according to the state Health Department. As SO2 is released from the summit and East Rift Zone vents, it reacts with atmospheric oxygen, sunlight, moisture, and other gases and particles and, within hours to days, converts to fine particles, which scatter sunlight, causing haze.

People have different reactions to vog, but exposure could worsen symptoms for people who have asthma or other respiratory conditions or cardiovascular disease. Also vulnerable are older adults and children, the health department said.

Even short-term exposure to sulfur dioxide can narrow the airways, causing asthma, or irritation of the eyes, nose, throat and skin, headaches, shortness of breath, or fatigue and dizziness, the department said.