Gaseous sulfur in the aerosol clouds produced by the eruptions of Mount St. Helens and El Chichón is the current focus of research on the effects of matter injected into the atmosphere by volcanoes. Recent research shows that new particles of sulfuric acid are formed up to 3 months after an eruption and that these particles can continue to grow for more than half a year following an eruption. These sulfuric acid particles may alter the earth's climate by interfering with the transmission of radiation from the sun into the lower atmosphere and of infrared radiation from earth back out to space. Furthermore, evidence published last month claims that sulfur emissions during noneruptive phases may be the main source of volcanic sulfur in the atmosphere.