Visibility

Visibility Condition

Visibility conditions use the difference between visibility (haze index) on mid-range days and the natural conditions. Condition categories (good, fair, poor) are based on the estimated five-year average of this value compared to NPS Air Resources Division  benchmarks .

Haziest Days Trends

Visibility trends on haziest days (10-year). The trend metric is the annual average haze index on the haziest days. Haziest days are the 20% of sampled days where visibility is most limited. NPS air quality analysis  methods  define significant trends as those with at least a 90% probability of being correct. 

Clearest Days Trends

Visibility trends on clearest days (10-year). The trend metric is the annual average haze index on the clearest days. Clearest days are the 20% of sampled days where visibility is most clear. NPS air quality analysis  methods  define significant trends as those with at least a 90% probability of being correct. 

Ozone

Human Health Condition

Ozone human health conditions use the fourth-highest daily maximum 8-hour average ozone concentration. Condition categories (good, fair, poor) are based on the estimated five-year average of this value compared to NPS Air Resources Division  benchmarks .

Human Health Trends

Ozone human health trends (10-year). The trend metric is the annual fourth-highest daily maximum 8-hour average ozone concentration. NPS air quality analysis  methods  define significant trends as those with at least a 90% probability of being correct. 

Vegetation Health Condition

Ozone vegetation health conditions use the 3-month maximum 12-hour W126 ozone metric, which relates plant response to cumulative ozone exposure. Condition categories (good, fair, poor) are based on the estimated five-year average of this metric compared to NPS Air Resources Division  benchmarks .

Vegetation Health Trends

Ozone vegetation health trends (10-year). The trend metric is the annual 3-month maximum 12-hour W126, which relates plant response to cumulative ozone exposure. NPS air quality analysis  methods  define significant trends as those with at least a 90% probability of being correct. 

Nitrogen

Nitrogen Condition / Ecosystem Response

The overall nitrogen ecosystem response condition gauges sensitivity of ecosystems and the general level of concern of harm. Condition categories (good, fair, poor) are based on a combination of individual conditions for 8 ecosystem components: herbaceous communities, herb occurrence, mycorrhizal communities, tree growth, tree survival, lichen communities, aquatic eutrophication, and alpine ecosystems. If a park has a poor condition, it is recommended to explore the individual components used in the assessment to better understand park sensitivities.

Nitrogen Condition / Wet Deposition

Nitrogen conditions use the nitrogen portion of wet nitrate (NO 3  -  ) and ammonium (NH 4  + ) deposition. Condition categories (good, fair, poor) are based on the estimated five-year average of this value compared to NPS Air Resources Division  benchmarks . 

Total Nitrogen Trends

Ten-year trends of the 3-year average estimated total (wet + dry) nitrogen (N) deposition are based on the maximum deposition value within a park’s boundary as estimated by the National Atmospheric Deposition Total Deposition (  TDEP  ). This approach combines measured and modeled data allowing for continuous analysis of ecosystem impacts across variation in topography, vegetation, and temperature. NPS air quality analysis   methods   define significant trends as those with at least a 90% probability of being correct. 

Nitrogen Trends

Wet nitrogen concentration trends (10-year). The trend metric is the annual precipitation-weighted mean concentration of the nitrogen portion of wet nitrate (NO 3  -  ) and ammonium (NH 4  + ). NPS air quality analysis  methods  define significant trends as those with at least a 90% probability of being correct. 

Nitrate Trends

Wet nitrate concentration trends (10-year). The trend metric is the annual precipitation-weighted mean wet nitrate (NO 3  -  ) concentration. NPS air quality analysis  methods  define significant trends as those with at least a 90% probability of being correct.  

Ammonium Trends

Wet ammonium concentration trends (10-year). The trend metric is the annual precipitation-weighted mean wet ammonium (NH 4  + ) concentration. NPS air quality analysis  methods  define significant trends as those with at least a 90% probability of being correct.

Sulfur

Sulfur Condition / Ecosystem Response

The overall sulfur ecosystem response condition gauges sensitivity of ecosystems and the general level of concern of harm. Condition categories (good, fair, poor) are based on a combination of individual conditions for 5 ecosystem components: herb occurrence, mycorrhizal communities, tree growth, tree survival, lichen communities, and aquatic eutrophication. If a park has a poor condition, it is recommended to explore the individual components used in the assessment to better understand park sensitivities.

Sulfur Condition / Wet Deposition

Sulfur conditions use the sulfur portion of wet sulfate (SO 4  2- ) deposition. Condition categories (good, fair, poor) are based on the estimated five-year average of this value compared to NPS Air Resources Division  benchmarks . 

Total Sulfur Trends

Ten-year trends of the 3-year average estimated total (wet + dry) sulfur (S) deposition are based on the maximum deposition value within a park’s boundary as estimated by the National Atmospheric Deposition Total Deposition (   TDEP   ). This approach combines measured and modeled data allowing for continuous analysis of ecosystem impacts across variation in topography, vegetation, and temperature. NPS air quality analysis    methods    define significant trends as those with at least a 90% probability of being correct.

Sulfate Trends

Wet sulfate concentration trends (10-year). The trend metric is the annual precipitation-weighted mean wet sulfate (SO 4  2- ) concentration. NPS air quality analysis  methods  define significant trends as those with at least a 90% probability of being correct. 

Mercury

Mercury Condition

Mercury condition use risk to wildlife from mercury as determined by available mercury concentration data in park fish, birds, and invertebrates (including  dragonflies ). Park-specific risks to wildlife are estimated by comparing mercury concentrations found in park fish, birds, and/or invertebrates to tissue and dietary health benchmarks (see NPS  mercury methods ).

Mercury Trends

Wet mercury concentration trends (10-year). The trend metric is the annual precipitation-weighted mean wet mercury concentration, measured in nanograms per liter (ng/L). NPS air quality analysis  methods  define significant trends as those with at least a 90% probability of being correct. 

Particulate Matter

Particulate Matter Condition

Particulate matter conditions use PM₂.₅ and PM₁₀ concentrations. Condition categories (good, fair, poor) are based on the Environmental Protection Agency's  human health-based Air Quality Index breakpoints  and the most conservative of the measured particulate metrics. Metrics considered include the 3-year average of the weighted annual mean PM₂.₅ concentration, 98th percentile 24-hour PM₂.₅ concentration, and 2nd maximum 24-hour PM₁₀ concentration.

Particulate Matter Trends

The overall trend in particulate matter concentrations (10-year). The trend metric is based on the weighted annual mean PM₂.₅ concentration, 98th percentile 24-hour PM₂.₅ concentration, and 2nd maximum 24-hour PM₁₀ concentration. Refer to NPS air quality analysis  methods  for trend combination logic. NPS air quality analysis  methods  define significant trends as those with at least a 90% probability of being correct.