Comparisons of coarse-mode aerosol nitrate and ammonium at two polluted coastal sites

Yeatman, S, Spokes, LJ and Jickells, TD (2001) Comparisons of coarse-mode aerosol nitrate and ammonium at two polluted coastal sites. Atmospheric Environment, 35 (7). pp. 1321-1335.

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Direct atmospheric fixed-nitrogen deposition can contribute to eutrophication in coastal and estuarine waters and can be enhanced by heterogeneous reactions between gaseous atmospheric nitrogen species and aerosol sea salt, which increase deposition rates. Size-segregated aerosol samples were collected from two coastal sites: Weybourne, England and Mace Head, Ireland. Major-ion aerosol concentrations were determined and temporal patterns were interpreted with the use of air-mass back trajectories. Low levels of terrestrially derived material were seen during periods of clean, onshore flow, with respective concentration ranges for nitrate and ammonium of 0.47-220 and below detection limit to 340nmolm-3. Corresponding levels of marine derived material during these periods were high, with sodium concentrations ranging from 39 to 1400nmolm-3. Highest levels of terrestrially derived material were seen during polluted, offshore flow, where the air had passed recently over strong source regions of the UK and northern Europe, with concentration ranges of nitrate and ammonium of 5.6-790 and 9.7-1000nmolm-3, respectively. During polluted flow ~40-60% of the nitrate was found in the coarse mode (>1µm diameter) and under clean marine conditions almost 100% conversion was seen. In addition, our data suggests strong evidence for dissolution/coagulation processes that also shift nitrate to the coarse mode. Furthermore, such processes are thought also to give rise to the size-shifting of aerosol ammonium, since significant coarse-mode fractions of this species (~19-45%) were seen at both sites. A comparison of the relative importance of nitrate and ammonium in the overall dry deposition of inorganic fixed-nitrogen at each site indicates that at Weybourne the mass-weighted dry deposition velocity of the latter is around double that seen at Mace Head with its resultant contribution to the overall inorganic nitrogen dry flux exceeding that of nitrate.

Item Type: Article
Faculty \ School: Faculty of Science > School of Environmental Sciences
Depositing User: Rosie Cullington
Date Deposited: 13 Jun 2011 09:33
Last Modified: 20 Mar 2023 12:35
DOI: 10.1016/S1352-2310(00)00452-0

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