During late 2024 and continuing through 2025, CASTNET added particulate matter (PM) monitoring capabilities as part of its modernization effort to all EPA-sponsored and IRL Council-sponsored CASTNET sites. Based on technical direction from EPA, WSP acquired and deployed QuantAQ MODULAIR and PurpleAir Flex sensors. QuantAQ and PurpleAir sensors are non-regulatory, lower cost, and low-maintenance instruments capable of providing high-temporal resolution measurements of PM_2.5 in real-time. These sensors deployed at rural CASTNET sites provide real-time information to communities that often lack other sources of air quality data, including locations impacted by wildfire smoke.

The continuous PM_2.5 concentration data from the PurpleAir sensors are included in the AirNow Fire & Smoke Map (https://fire.airnow.gov/) to fill in spatial gaps in the regulatory monitoring network. The map provides local air quality conditions (PM_2.5) from regulatory monitors and non-regulatory sensors combined with fire locations and smoke plumes detected by satellites. The map is used as a resource to make informed decisions to protect community health during periods of poor air quality.

QuantAQ sensors deployed at CASTNET sites include two different models - PM-only (PM₁, PM_2.5, and PM₁₀) and PM plus four gas-phase measurements (CO, NO, NO₂, and ozone), with the gas measurements based on solid-state sensors. WSP has installed MODULAIR models with gas measurements at filter-pack only sites where FEM ozone measurements are not available. These sensors provide additional information about the spatial distribution of pollutants and are particularly effective in capturing data during non-routine sampling events like wildfires or rocket launches.