TRENDS, SEASONAL-VARIATIONS, AND ANALYSIS OF HIGH-ELEVATION SURFACE NITRIC-ACID, OZONE, AND HYDROGEN-PEROXIDE

Atmospheric photochemical oxidants nitric acid, ozone, and hydrogen pe roxide were monitored in ambient air at Mt Mitchell State Park, North Carolina. Ozone measurements made from May to September during 1986-19 90 are reported for two high-elevation sites (Site 1 on Mt Gibbs, appr oximately 2006 m; and Site 2 on Commissary Ridge, approximately 1760 m ). These measurements are also compared to those from a nearby, low-el evation site (Fairview, approximately 830 m). Average ozone concentrat ions increased from lower to higher elevations. Meteorological analysi s shows an association between periods of high ozone concentrations an d synoptic-scale patterns. No discernible diurnal cycle in the ozone c oncentrations was observed at Site 2; however, a reversed diurnal cycl e (nighttime maximum) was evident at Site 1. Gas-phase hydrogen peroxi de and nitric acid concentration were measured at Site 1 during 1988 a nd 1989, and typically range from 0 to 4 ppbv, and 0-2 ppbv, respectiv ely. Seasonal analysis shows that the ozone maximum occurs during spri ng coincident with the spring maximum at Whiteface Mountain, NY, Mauna Loa in Hawaii, and at Alpine stations in Europe, suggesting that ozon e production is a hemispheric rather than local phenomenon and that th e underlying phenomenon affects perhaps the entire Northern Hemisphere . The diurnal cycle of gaseous hydrogen peroxide was similar to the hi gh-elevation ozone signal, while gaseous nitric acid concentration pea ked during the day. This apparent discrepancy in the diurnal cycle bet ween the three atmospheric photochemical oxidants at high elevation ma y be due to a difference in the behavior of the altitudinal gradients of those oxidants resulting from a combination of photochemistry, mete orology and dynamic processes.