Measurements of atmospheric hydrogen peroxide in the gas phase and in cloud water at Mt. Mitchell, North Carolina

Measurements of atmospheric hydrogen peroxide in the gas phase were made during four intensive observation periods at the Mt. Mitchell State Park, North Carolina, during the growing season (May through September) of 1988. Cloud water hydrogen peroxide was measured during the entire field season of 1988 and during the late summer and fall of 1987 (August and October). Cloud water concentrations were found to be similar to those reported from another high‐elevation location in the southeastern United States. Cloud water samples collected during these periods showed a wide range of levels (∼ 0 – 219 μM/L ) and average values of 38 μM/L and 44 μM/L for the entire sampling seasons of 1988 and 1987, respectively. Significant seasonal variation was noted both in 1987 and 1988, with cloud water levels of hydrogen peroxide much higher in the summer than in the fall. Gas‐phase hydrogen peroxide levels ranged from the detection limit (0.1 ppbv) to above 4 ppbv. Gas‐phase hydrogen peroxide demonstrated a nighttime maximum in the summer but not in the fall. The measurements taken in the fall were significantly lower than those taken during the summer, possibly due at least in part to seasonal variation. Atmospheric hydrogen peroxide levels were found to be increasing during stagnating high‐pressure systems and were found to correspond to the back trajectory of the air mass with the highest concentrations corresponding to continental air masses. The hydrogen peroxide concentration was also found to be affected by radical formation from ozone and by loss processes such as wet and dry deposition.