Before the South32 Hermosa Project becomes fully operational, community watchdogs in eastern Santa Cruz County are stressing the need for an independent, long-term record of local air quality. Establishing that baseline now is essential: without reliable information about existing conditions, residents will have no clear way to determine whether air quality changes as construction, traffic and mining increase.
The Hermosa Project is located approximately five miles south of Patagonia in the Patagonia Mountains. It is being developed as an underground mine initially targeting zinc, lead and silver deposits, with future potential development of tapping into a manganese deposit. The Arizona Department of Environmental Quality (ADEQ) issued an updated Class I air-quality permit for the project in February 2026 following federal review.
For residents of Patagonia, Sonoita, Harshaw, Elgin and surrounding rural areas, the central question is not simply whether the mine will meet its permitted emission limits. It is whether residents can document what the air is like before full-scale operations begin and then compare those conditions with measurements collected over the years that follow.
There are currently three sources of information.
South32 has established air-quality monitoring stations near Patagonia, Nogales and Sonoita. The program measures total suspended particles and analyzes collected material for metals, including manganese, lead, zinc, silver and copper. Weather information, including wind speed and direction, is also recorded.
ADEQ provides the regulatory framework and is responsible for enforcing the project’s air-quality permit.
A third effort may be especially valuable to residents: the AirSMART Network, a community monitoring project involving researchers from the University of Arizona and Arizona State University and the Calabasas Alliance.
AirSMART uses relatively small, low-cost sensors capable of providing frequent, real-time measurements of particulate pollution and other atmospheric conditions. The program currently has 17 monitoring stations in Santa Cruz County, including four in Patagonia, two in Sonoita, where one was recently installed at the Sonoita-Elgin Fire District station, one in the Patagonia Mountains and one in the Patagonia Lake area. The project provides the possibility of much more localized monitoring than a small number of regulatory stations can provide.
These systems do not measure exactly the same pollutants or use identical methods. That is not necessarily a weakness. In fact, the differences can make them complementary.
South32’s sampling can provide laboratory information about metals in airborne particles. AirSMART can help identify when and where particulate levels change. ADEQ provides regulatory oversight.
Together, these sources could provide a far better picture than any one system alone.
Dr. Chris Lim from Arizona State University recently gave a presentation to the Santa Cruz County Board of Supervisors and spoke with the PRT afterward. He said the monitoring program has been ongoing for about a year and that it hopes to add more sensor locations.
“As we collect more data, we’ll be able to take a closer look at the trends, both short-term and long-term, the sources of pollution and how it’s changing,” Dr. Lim said.
The most useful information will not be a single reading. It will be patterns over time. A single elevated reading does not prove that the mine caused it. Likewise, a reading below a regulatory limit does not necessarily answer every question a community may have about local air quality. That is why long-term trends and comparisons are important.
There is a natural tension whenever an industrial operation is responsible for monitoring emissions associated with its own project. That does not mean company-collected data are unreliable. It does mean that independent measurements provide an important additional level of confidence. The university/community monitoring effort is therefore particularly significant.
The temptation with any baseline study is to think of it as a one-time snapshot. It shouldn’t be. Air quality naturally changes with seasons, drought, wind, wildfires, dust, traffic and other factors. The longer the record, the easier it becomes to distinguish those normal variations from changes that may coincide with mine construction or operations.
Monitoring data is available to the public.
AirSMART’s real-time data is available on its monitoring website: aq-sensors.shinyapps.io/AirSMART/.
South32 provides information its air-quality dashboard from its monitoring network near Patagonia, Nogales and Sonoita: https://south32.advm2.net/public/#/.
ADEQ’s Hermosa Project webpage provides the official air-quality permit and related technical and regulatory documents: https://azdeq.gov/wqd/hermosa-south32.