South Coast AQMD Issues Odor Advisory for Eastern Coachella Valley, valid through Tuesday July 27, 2021.
This advisory is in effect through Tuesday evening. South Coast AQMD will issue an update if additional
information becomes available. The South Coast Air Quality Management District has issued an odor advisory for the Eastern Coachella Valley due to elevated levels of a gas that smells like rotten eggs. That gas, hydrogen sulfide, is associated with natural processes occurring in the Salton Sea. South Coast AQMD monitors hydrogen sulfide at three locations in the Eastern Coachella Valley, one very close to the Salton Sea, one in the community of Mecca, and one in Indio. On Sunday morning, winds out of the southeast brought elevated hydrogen sulfide concentrations into the Eastern Coachella Valley. Hydrogen sulfide concentrations reached 48 parts per billion (ppb) at a monitor close to the shore, 52 ppb at a monitor in Mecca, and 31 ppb at a monitor in Indio. Over the past several days, the highest concentrations at both monitors have occurred when winds were blowing out of the southeast, especially during the overnight and morning hours when the atmosphere is more stable
Winds from the southeast are expected from approximately 11 AM to 5 PM on Monday and during daylight hours on Tuesday, possibly leading to elevated concentrations at the Near-Shore, Mecca and Indio community sites. However, forecasted showers and thunderstorms on Sunday evening and on Monday may help reduce hydrogen sulfide levels due improved atmospheric mixing and the cleansing effect of rainfall. The state standard for outdoor levels of hydrogen sulfide is 30 ppb averaged over one hour. At that level, most individuals can smell the odor and some may experience symptoms such as headaches and nausea. However, the symptoms associated with this level of exposure are temporary and do not cause any long-term health effects. Humans can detect hydrogen sulfide odors at extremely low concentrations, down to a few parts per billion.