Documented 50-Year change in acidity and chemistry of New England fog

Jagles, Richard; Cunningham, Robert; Carlisle, Jonathan; Day, Michael

This is a report that cumulatively uses New England fog data to model and analyze acid fog conditions from 1939 to 1994. Though this study uses data collected from coastal Maine sites (Isle au Haut) for modeling, no new data were collected in the park for this particular study/report. ' In 1939, fog was collected and analyzed by the second author and Alan Bemis and H.G. Houghton at several New England sites. Two types of collectors were used, but only one (stainless steel screen) provided contaminent-free collection. Fog pH and sulphate were measured, but nitrate and ammonium levels were not measured. In 1989, we collected fog at one of the original contaminent-free sites and measured pH, sulphate, nitrate, and ammonium levles. Data were also referenced to our other nearby coastal fog-monitoring sites where we have ten years of fog chemistry data. Using regional and local models we calculated the projected historical levels of ammonium for the mid-coast of Maine, circa 1939. Seven different sets of previously published emission factors were incorporated into our models which pedicted a range of 1939 levels, and a mean percent change of 1.6 over 50 years. The thirty-one fogs collected in 1989 had mean and (median) pH values of 3.39 and (3.49), while from 1939 eleven of fogs had an average pH of 4.03 and (4.40). The average pH of mid-coast Maine fogs over ten years (1985-1994) was 3.30 and (3.42) and varried little from year to year. Average SO4 2- for 1989 (marine corrected) was 395 (330) Meql-1 and for 1939 was 316 (204) Meql-1. Average NO3 for 1989 was 234 (218) Meql-1. Using the mean ammonium predicted from the modles for 1939 (approximated as 0% change), the 1939 NO3 levles should have been close to zero. Thus, within reasonable estimates, the fog acidity has increased from 4 to 10 fold (from mean and median statistics repectivley) and this has been driven primarily by increases in NO3 levels, presumably as a reult of increased NOx emmissions from east cost meteropolitan areas.'