The most critical factors that determine how much vog impacts an area are wind direction and speed. Air temperature, humidity, rainfall, location of the source, and the amount of sulfur dioxide (SO2) being emitted are also factors.
During prevailing trade (from northeast) wind conditions, any SO2 emitted from Pu`u `Ō`ō is blown out to sea, while any SO2 from the summit vent often creates vog in Ka`u communities from Pahala to Ocean View. SO2 emissions from the Lower East rift zone blow downwind to the Kona coast. Unfortunately, multiple plumes can eventually reach the west side of Hawai`i Island in a "double-whammy" of combined effects, resulting in an especially dense and nearly constant haze of vog along the Kona coast.
When the winds become light and variable or blow from the south, communities in East Hawai`i and along the entire Hawaiian Island chain can also suffer the effects of vog. Under these conditions, people living in the path of gas emissions continue to experience vog levels similar to those that have beset them for over two decades. Communities in the path of summit SO2 emissions, particularly those nearest the source vent, can be subjected to an unusually acrid haze that contains both gas and acidic particles because the emissions have had little time to disperse and dilute before reaching them.