A meteorological analysis of the precipitation chemistry event samples at Hubbard Brook (N.H.)

On 100 occasions over a 3-y period ( June 1975 to July 1978 inclusive), precipitation collected at the Hubbard Brook Experimental Forest was analyzed for its chemical constituents. The present paper is a meteorological examination of the data, using back trajectories based on a quasi-geostrophic method. Some of the trajectories are complex and difficult to interpret. When these are excluded, the remaining 69 events show the influence of meteorology on wet deposition at Hubbard Brook. Highest values of H +, SO 4 and NO 3 are associated with winds from the SSE through SSW, and with looping trajectories over New England. In contrast, air that has come from the NNW-NE-ESE sector is relatively clean. These results are confirmed using a crossing-trajectory analysis. A method of trend analysis for SO 4 concentrations is suggested, using crossing-trajectory statistics and a simple linear chemistry model. The sample period (3 y) is too short to provide a fair test of the method. Nevertheless, the results obtained are not unreasonable, namely a downward trend of 7% in SO 4 concentrations, when the data are normalized for meteorological factors, as compared with a decrease of 5 % in regional emissions of SO 2 over the same period.