Phase partitioning and dry deposition of atmospheric nitrogen at the mid-Atlantic U.S. coast

Abstract

The deposition of atmospheric nitrogen contributes significantly to total nitrogen (TN) entering U.S. coastal water bodies. Nitrogen inputs via wet deposition are well quantified but dry-deposition fluxes are uncertain. In this study, dry fluxes of major atmospheric nitrogen species (including gaseous NH3 and HNO3 and particulate NH4+, NO3-, NO2-, and organic nitrogen (ON)) were quantified during a 2-week summer sampling period at Lewes, Delaware, on the mid-Atlantic U.S. coast. Results indicate that dry deposition contributed approximately 43% to total atmospheric nitrogen deposition. Under all flow conditions, NH3(g) accounted for the largest fraction of TN dry deposition (averaging 60%); HNO3(g) and NO3- also contributed considerably (averaging 25 and 8%, respectively). During onshore flow, scavenging of HNO3(g by sea-salt aerosols shifted the phase partitioning and relative dry fluxes of total NO3 (HNO3(g) + NO3-) toward particulate NO'3-. The mass-weighted deposition velocities for particulate NO3 (associated primarily with sea-salt size fractions) were similar to those of HNO3(g). Consequently, phase changes did not substantially alter the dry-deposition fluxes of total NO3. In light of these results, dry-deposition monitoring programs at coastal locations should (1) quantify NH3(g) deposition; (2) reliably sample supermicron particles (with which most particulate NO3- is associated); and (3) apply deposition models for particulate nitrogen that are consistent with corresponding size distributions. Copyright 2003 by the American Geophysical Union.