Description: <p>The trend metric is the annual precipitation-weighted mean wet mercury concentration, measured in nanograms per liter (ng/L). All improving and deteriorating trends have at least 90% probability of being correct (those with p-values ≤ 0.10). Statistically significant (p-value ≤ 0.10) trends with zero slope are represented as unchanging trends. Parameters with no statistically significant trend (p-value ≥ 0.10) are also represented as unchanging trends. See NPS air quality analysis methods for more information: https://www.nps.gov/articles/air-analysis-methods-latest.htm.</p>