The Heartland Vital Signs Network (HTLN) consists of 15 NPS units located in eight Midwestern states (Arkansas, Indiana, Iowa, Kansas, Minnesota, Missouri, Nebraska, and Ohio). The parks include cultural, historical and natural areas, and host a diversity of terrestrial and aquatic ecosystems associated with tall grass prairies, Eastern broadleaf deciduous forests, interior highlands, and the Mississippi River embayment. All 15 units are designated Class II air quality areas.
Few of the Network parks have on-site ambient air quality monitoring. In fact, there are relatively few air quality monitors in the central U.S. Surface waters in Network parks appear to be well-buffered, so atmospheric deposition is not a threat. The air pollutant of concern for the HTLN is ozone. While only one of the Network parks, Cuyahoga Valley National Recreation Area in Ohio, is in a proposed 8-hour ozone non-attainment area, lack of monitoring may underestimate the ozone problem in Network parks. An ozone injury risk assessment indicates the risk of injury is moderate to high in six HTLN parks.
The Network map below provides information on air quality monitoring. Ozone, sulfur dioxide, dry deposition, and meteorology are collected by the Clean Air Status and Trends (CASTNet) network. Ozone is also monitored with passive samplers and portable continuous analyzers. Wet Deposition is monitored through cooperation with National Atmospheric Deposition Program/National Trends Network (NADP/NTN). The Mercury Deposition Network (MDN), part of NADP, collects precipitation samples that are analyzed for mercury. Visibility is monitored as part of the Interagency Monitoring of Protected Visual Environments (IMPROVE). Additional details on these parameters are described in Air Quality Monitoring.
Air quality monitoring in or near the network is indicated on the map by symbols, with the blue line showing the approximate borders of the network. The legend shows the symbols for the type of monitoring present, with NPS park units in green.