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

Measurements of airborne (gaseous and aerosol), cloud water, and precipitation concentrations of ammonia (NH3) and ammonium (NH+4) compounds were made at Mt. Mitchell State Park (Mt. Gibbs, 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 NH+4 and nitrate (NO-3) compounds. Measurements of NH+4 in cloud and rain water samples were made during the same time period. Mean concentrations of gaseous NH3 were 0.62 μg m-3 for 1988 and 1.47 μg m-3 for 1989. Mean concentrations of fine particulate NH+4 were 1.24 μg m-3 for 1988 and 0.89 μg m-3 for 1989. The NH+4 concentrations in the cloud water were 214 and 147 μeq ℓ-1 for the 1988 and 1989 field seasons, respectively. The concentrations of NH+4 in precipitation were quite low compared to cloud ionic values in both 1988 and 1989 at 14 and 15 μeq ℓ-1, respectively. The estimated mean total deposition of NH+4 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 ( 70%) to the total deposition than combined wet ( 15%) and dry ( 15%) deposition.