Analysis of ammonia and aerosol concentrations and deposition near the free troposphere at Mt. Mitchell, NC, USA

Measurements of airborne (gaseous and aerosol), cloud water, and precipitation concentrations of ammonia (NH3) and ammonium (NH4+) compounds were made at Mt. Mitchell State Park (Mt. Gibbs, similar to 2006 m MSL), North Carolina. Measurements were made from May to September during 1988 and 1989. An annular denuder system was used to determine gaseous NH3 and particulate NH4+ and nitrate (NO3-) compounds. Measurements of NH4+ in cloud and rain water samples were made during the same time period. Mean concentrations of gaseous NH3 were 0.62 mu g m(-3) for 1988 and 1.47 mu g m(-3) for 1989. Mean concentrations of fine particulate NH4+ were 1.24 mu g m(-3) for 1988 and 0.89 mu g m(-3) for 1989. The NH4+ concentrations in the cloud water were 214 and 147 mu eq l(-1) for the 1988 and 1989 field seasons, respectively. The concentrations of NH4+ in precipitation were quite low compared to cloud ionic values in both 1988 and 1989 at 14 and 15 mu eq l(-1), respectively. The estimated mean total deposition of NH4+ over the sampling period (5 months) of 1988 and 1989 was about 0.38 and 0.67 g N m(-2) season(-1), respectively. Cloud water interception contributed more nitrogen (similar to 70%) to the total deposition than combined wet (similar to 15%) and dry (similar to 15%) deposition. (C) 1998 Elsevier Science Ltd. All rights reserved.