What damaging pollutant is NOT closely tracked by the US EPA?

One damaging pollutant that is not closely tracked by the US EPA is ammonia. While ammonia can contribute to air and water pollution and has significant environmental impacts, it is not regulated under the Clean Air Act or the Clean Water Act in the same way that other pollutants, such as nitrogen oxides or particulate matter, are. This lack of monitoring can lead to underestimations of its effects on ecosystems and human health.