Description: The Clean Air Status and Trends Network (CASTNET) provides atmospheric data on acid rain, tropospheric (ground-level) ozone and other forms of atmospheric pollution. Used in conjunction with other national monitoring networks, CASTNET is used to determine the effectiveness of national emission control programs. CASTNET has been operating since 1987 and is considered the nation's primary source for estimates of dry acidic deposition and rural ozone levels. Cooperatively funded and operated with the National Park Service, the network is comprised of over 70 sites across the eastern and western United States.
| Compound | CASTNet Species | CMAQ Mapping | REMSAD Mapping |
| Gaseous HNO3 | NHNO3 (nylon filter) | 2176.9*DENSa*HNO3 | HNO3 |
| Particulate NO3 | TNO3 (Teflon filter) | ANO3J + ANO3I | PNO3 |
| Particulate NH4 | TNH4 (Teflon filter) | ANH4I + ANH4J | NH4S + NH4N |
| Gaseous SO2 | TOTAL_SO2 | 2211.5*DENS*SO2 | SO2 |
| Particulate SO4 | TSO4 (Teflon filter) | ASO4I + ASO4J | GSO4 + ASO4 |
| Particulate NO3+SO4 | 0.29*TNO3 + 0.375*TSO4 | 0.29*(ANO3I + ANO3J) + 0.375*(ASO4I + ASO4J) | 0.29*PNO3 + 0.375*(GSO4 + ASO4) |
| Total NO3 (gas+particle) | TOTAL_NO3 | ANO3I + ANO3J + 0.9841*(2176.9*DENS*HNO3) | PNO3 + 0.9841*HNO3 |