Trends, Seasonal Variations, and Analysis of High-elevation Surface Nitric Acid, Ozone, and Hydrogen Peroxide

Atmospheric photochemical oxidants nitric acid, ozone, and hydrogen peroxide were monitored in ambient air at Mt Mitchell State Park, North Carolina. Ozone measurements made from May to September during 1986-1990 are reported for two high-elevation sites (Site I on Mt Gibbs, approximately 2006 m; and Site 2 on Commissary Ridge, approximately 1760 m). These measurements are also compared to those from a nearby, low-elevation site (Fairview, approximately 830 m). Average ozone concentrations increased from lower to higher elevations. Meteorological analysis shows an association between periods of high ozone concentrations and synoptic-scale patterns. No discernible diurnal cycle in the ozone concentrations was observed at Site 2; however, a reversed diurnal cycle (nighttime maximum) was evident at Site 1. Gas-phase hydrogen peroxide and nitric acid concentration were measured at Site 1 during 1988 and 1989. and typically range from 0 to 4 ppbv, and O-2 ppbv, respectively. Seasonal analysis shows that the ozone maximum occurs during spring coincident with the spring maximum at Whiteface Mountain, NY, Mauna Loa in Hawaii, and at Alpine stations in Europe, suggesting that ozone production is a hemispheric rather than local phenomenon and that the underlying phenomenon affects perhaps the entire Northern Hemisphere. The diurnal cycle of gaseous hydrogen peroxide was similar to the high-elevation ozone signal, while gaseous nitric acid concentration peaked during the day. This apparent discrepancy in the diurnal cycle between the three atmospheric photochemical oxidants at high elevation may be due to a difference in the behavior of the altitudinal gradients of those oxidants resulting from a combination of photochemistry, meteorology and dynamic processes. Key word index: Nitric acid, ozone, hydrogen peroxide, photochemical oxidants, high elevation.