Dry deposition and dew chemistry in Claremont, California, during the 1985 nitrogen species methods comparison study

Abstract

Dry deposition of HNO 3 and aerosol nitrate in Claremont, California, during the September 1985 Nitrogen Species Methods Comparison Study was evaluated by means of nylon and Teflon surrogate-surface collectors. Dew chemistry and deposition to dew were also investigated. The nitrate dry deposition was governed largely by HNO 3; most of the dry deposition of inorganic nitrate (defined here as HNO 3(g) plus aerosol nitrate) onto the surrogate collectors occurred in the daytime, reflecting chiefly a greater-than-10-fold diurnal variation in ambient HNO 3 (g) concentration. In the absence of dew, deposition velocities were ~1.3cms −3 for HNO 3(g), ~0.2cms −1 for aerosol nitrate, and 0.5cms −1 for nitrate without distinction between the two species. Night-time nitrate deposition velocities appeared to be lower when there was dew. The total titratable acidity of the dew, though considerable (~ 50 μM), was not present chiefly as free acidity (H +); the average pH was only ~ 5. Preliminary evidence suggests that some of the titratable dew acidity was derived from organic acids. These results are compared to dry deposition and dew chemistry in other areas.