Date

2016-10-10

Author

Nehir, Münevver

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Two stage aerosol (coarse: PM10-2.5 and fine: PM2.5) and rainwater samples were collected at a rural site (Erdemli) located on the coast of the eastern Mediterranean, between January 2014 and April 2015. Concentrations of the water-soluble nitrogen species (organic nitrogen (WSON), nitrate, ammonium, total nitrogen (WSTN) and urea) were measured in a total of 740 aerosol and 23 rainwater samples. Among the nitrogen species, WSON (24.6 ± 16.3 nmol N m-3) denoted the highest arithmetic mean and followed by ammonium and nitrate concentrations in aerosol samples. Approximately 61% of the WSON was associated with coarse particles though the remaining fraction (39%) was accompanied with fine particles. Correspondingly, WSON contributions to WSTN in coarse and fine mode were found to be around 47.6 and 28.1 %. The volume weighted mean concentration of WSON was around 21.5 μM N in rainwater. Relative contribution of WSON to WSTN (73.5 μM N) was 29.3 % in rainwater. The urea mean concentration in coarse mode with standard deviations of 2.7 ± 2.7 nmol N m-3 and in fine mode 1.7 ± 1.7 nmol N m-3. Around 61 % of the urea was associated with coarse mode aerosol, whilst the remaining 39 % was associated with fine mode aerosol. Urea relative contributions to WSTN in coarse and fine mode were 8.5 and 4.9 %, and to WSON in coarse and fine mode were 18 and 18 %, respectively. The daily variability in the concentration of water-soluble nitrogen species including WSON and urea may be an order of magnitude. The lowest concentrations of water-soluble nitrogen species were found to be associated with rainy days. Relatively higher values of these water-soluble species were observed in summer and these concentrations might be attributed to the lack of wet deposition and re-suspension of cultivated soil. However, water-soluble organic nitrogen and urea exhibited the highest concentrations when air masses back trajectories originated from desert regions located at North Africa and the Middle East. For instance, one of the highest WSON (66.1 nmol N m-3) and urea (19.8 nmol N m-3) concentrations were observed on March 2, 2014 when the air mass back trajectories originated from Sahara and the Middle East deserts. Monthly mean concentrations of WSON and urea in coarse mode indicated inverse correlations with rain amount which suggested that these particles were removed from atmospheric compartment efficiently by wet deposition. Moreover, WSON and urea in coarse particles demonstrated inverse relationship with temperature and it might be ascribed to re-suspension of cultivated soil. During the study period 45 dusty days were determined by a sharp increase in the concentration of nns-Ca2+. Regarding dust and non-dust event, WSON and urea demonstrated 1.3 and 2 times higher concentrations during dust events compared to those of observed for non-dust events, respectively. The mineral dust episodes also affected the relative distributions of particles, coarse mode being dominant during the dust-events. The lowest WSON concentration was associated with air masses originated from Russia while the highest values were observed airflow from the Middle East and North Africa. The calculated PM10-2.5/ PM2.5 ratios of WSON for these airflows were higher than 1.15, denoting dominance of coarse fraction. The lowest urea concentrations were found when airflow derived from Russia, Northern Turkey and Middle East, with concentrations of 2.7, 2.9 and 2.3 nmol N m-3, respectively. Whereas, there was a distinct difference between their PM10-2.5/ PM2.5 ratio, suggesting airflow from Russia and Northern Turkey was equally influenced by fine and coarse particles whilst air masses from Middle East was mainly dominated by coarse particles. It might be argued that airflow originating from Middle East had more natural sources compared to anthropogenic sources. Positive matrix factorization (PMF) analysis was applied to clarify sources of WSON and urea. Results denoted that 77 % and 10 % of the WSON was derived from the re-suspension of cultivated soil and sea-salt particles, respectively. Nevertheless, 27 % of the urea was held by re-suspension of cultivated soil while 49 % of urea was found to be associated with nitrate, implying reaction between alkaline urea and acidic nitrate. Atmospheric fluxes of WSON and nitrate were almost equally influenced by dry and wet deposition, whereas ammonium flux was dominated by wet deposition (92 %). Annually, the atmospheric fluxes of WSON and nitrate were calculated 20.5 and 21.6 mmol m-2 yr-1, respectively, whilst the atmospheric ammonium flux was found 15.6 mmol m-2 yr-1. Based upon to detected new production in the surface waters of the Eastern Mediterranean, the atmospheric water-soluble nitrogen fluxes were determined to assist 33 % of the production in coastal waters and 76 % of the production in open waters. The observed new production between June and October when stratification occurs was found to be around 2 C mg m-2 day-1. During this period, atmospheric nitrogen can support new production in the Cilicia Basin up to 6 times.

Subject Keywords

aerosol, wet deposition, water-soluble nitrogen species, mineral dust, long range transport, atmospheric input, marine productivity, Eastern Mediterranean

URI

https://hdl.handle.net/11511/95095

Collections

Graduate School of Marine Sciences, Thesis