During 2025, 20 particle sensors located in Santa Cruz County began contributing data to document a scientific baseline understanding of local outdoor air quality. The local placement of these sensors was facilitated by the Calabasas Alliance, a Rio Rico-based group that advocates “for responsible environmental stewardship and sustainable alternatives to mining in Santa Cruz County,” according to their mission statement.
Calabasas Alliance teamed up with researchers at Arizona State University and the University of Arizona to help deploy a citizen-powered outdoor air quality monitoring program they call Air Smart.
With installation help from University of Arizona graduate students, the Air Smart program helped place sensors in SC County in mid-2025. In Eastern Santa Cruz County, five are currently operating in or very near Patagonia town limits and one in Sonoita. Another three sensors are located in the vicinity of Lake Patagonia, and there are several more in the Santa Cruz River Valley.
The sensors resemble puffball mushrooms and are powered by about 5 watts of household electricity. Using tiny lasers, they detect PM2.5, a particle size of 2.5 microns in size, or smaller. Particulate matter sized at that level—about 1/40th the diameter of a human hair—is a critical size for air quality research, as these tiny particles float in air and can travel far, penetrate deep into the lungs and then enter the bloodstream. At this small size, the particles might be dust, pollen, soot from fossil fuel vehicles or domestic heating, mineral dust from manufacturing or mining, gravel processing, dirt roads, volcanoes or wildfire smoke.
A facilitator for the Air Smart Program is Dr. Chris Lim, an Associate Professor at the University of Arizona’s School of Public Health specializing in Air Epidemiology.
“It is important to remember that just measuring particles by size doesn’t identify their composition,” Dr. Lim said. The particle sensors in the Air Smart program can measure the concentration of particles in the air, but cannot identify the source of those particles. Dr. Lim said that the long-term plan, depending on grant funding, is to add more particle and gas sensors, as well metal detection capabilities, in the sensor regions. Sensors that can analyze gases and detect minerals have the potential to more directly track health hazards like lead and manganese.
The sensors use WiFi connections to transmit data every five or ten minutes to a web-based company called Purple Air, which maintains an interactive online air quality map.
PurpleAir and most other air quality maps display this massive flow of data using the scientifically based Air Quality Index (AQI) devised by the Environmental Protection Agency as a measure of threat level to human health. Nationally, people are beginning to use these ratings to plan exercise or outdoor activity, keep children indoors or not, or, if ratings are very low, get out and enjoy.
An Oct. 21 screenshot from Purple Air showed as good a day as possible in the Patagonia area: all five sensors read zero.
The Town of Patagonia’s particle sensor is near the gazebo in its central park, and the Town also has a more sophisticated sensing instrument, a little box called Quant AQ. Besides measuring three levels of particulate matter, the Quant AQ units also measure carbon monoxide, nitrogen oxides and ozone. Along with sulfur dioxide, these are the primary pollutants of concern and regulation by the national Clean Air Act, enforced by the federal Environmental Protection Agency.
The data from both particulate and gas sensors are building a robust air quality baseline for the Town and the rest of Santa Cruz County. Mayor Wood confirmed that the Town supports the Air Smart program. She is looking forward to seeing the data.
The monitoring of air is also of concern to South32. “Air quality,” wrote Hermosa South32’s Community Lead Taja Vivens in a Sept. 24 email, “is one of several resource areas currently being discussed as part of the Community Benefits and Protections Agreement (CBPA),” adding that “the conversations include monitoring, response, and community priorities.”