Summer-time distribution of air pollutants in Sequoia National Park, California

Concentrations of air pollutants were monitored during the May–November 1999 period on a network of forested sites in Sequoia National Park, California. Measurements were conducted with: (1) active monitors for nitric oxide (NO), nitrogen dioxide (NO2) and ozone (O3); (2) honeycomb denuder/filter pack systems for nitric acid vapor (HNO3), nitrous acid vapor (HNO2), ammonia (NH3), sulfur dioxide (SO2), particulate nitrate (NO3−), ammonium (NH4+), and sulfate (SO42−); and (3) passive samplers for O3, HNO3 and NO2. Elevated concentrations of O3 (seasonal means 41–71 ppb), HNO3 (seasonal means 0.4–2.9 μg/m3), NH3 (seasonal means 1.6–4.5 μg/m3), NO3− (1.1–2.0 μg/m3) and NH4+ (1.0–1.9 μg/m3) were determined. Concentrations of other pollutants were low. With increasing elevation and distance from the pollution source area of O3, NH3 and HNO3 concentrations decreased. Ammonia and NH4+ were dominant N pollutants indicating strong influence of agricultural emissions on forests and other ecosystems of the Sequoia National Park.