Organic nitrogen in rain and aerosol in the eastern Mediterranean atmosphere: An association with atmospheric dust

Abstract

From March through early May of 2000, rain and bulk aerosol samples were collected at a coastal site on the eastern Mediterranean Sea at Erdemli, Turkey, and analyzed for nitrogen (N) species, including nitrate (NO3−), nitrite (NO2−), ammonium (NH4+), water‐soluble organic N, urea, and dissolved free amino acids. Other ions were also analyzed, including Ca2+, Mg2+, K+, Na+, Cl−, and SO42−. Water‐soluble organic N was found to contribute ∼17% and ∼26% of the total water‐soluble N in rain and aerosols, respectively. Organic N concentrations within rain and aerosols exhibited statistically significant linear relationships to Ca2+ ion (Rsqr ∼ 0.75, P < 0.05), suggesting a relationship to calcite (CaCO3) in atmospheric dust. Kinematic trajectory analyses indicated the origin of winds from arid regions, mainly in northern Africa, in 70% of the aerosols sampled. Earth Probe/Total Ozone Mapping Spectrometer aerosol index data also confirmed the influence of atmospheric dust in the region on days when Ca2+ concentrations were elevated, and trajectory analyses suggested northern Africa as a source region. The combined ion, trajectory, and aerosol index data suggest that organic N is associated with atmospheric dust in this region. Urea N and amino N represented a small percentage of the organic N fraction. In rain and aerosols, urea represented ∼11% and <1%, respectively, of the total organic N. While amino N contributed minimally to organic N totals (∼1% of total organic N in aerosols), the individual amino acids contributing ∼75% of amino N were indicative of biological organisms. Further research is needed to decipher the influence from biology and gas phase adsorption of anthropogenically derived water‐soluble organics on organic N totals.

Atmospheric water-soluble organic nitrogen (WSON) in the eastern Mediterranean: origin and ramifications regarding marine productivity

“…The maximum concentration of WSON was estimated to be 79 nmol N m −3 , with a mean value and standard deviation of 23.8 ± 16.3 nmol N m −3 . The observed arithmetic was comparable to that reported by Mace et al (2003a) for the same site. Approximately 66 % of the WSON was associated with coarse particles; the remaining fraction (34 %) was present within the fine mode.…”

“…Percent contributions of coarse WSON for dust and non-dust events were almost identical, being 58 and 60 %, respectively. A similar enrichment of WSON during dust events has been reported for Erdemli (Mace et al, 2003a), the Yellow Sea (Shi et al, 2010) and Finokalia . In addition, Griffin et al (2007) have demonstrated a significant difference between dust and non-dust events for bacterial-and fungalcolony-forming units at Erdemli, the former being much greater.…”

“…Such high values were ascribed to natural fires (Mace et al, 2003c). The mean WSON concentration at Erdemli (23.8 nmol N m −3 ) was comparable to that reported previously for the same site (29 nmol N m −3 , Mace et al, 2003a). In contrast, the present WSON concentration was almost 1.5 times higher than that observed at Finokalia .…”

“…Such high values are not unusual. For example, if the data presented by Mace et al (2003a) had been used, precisions would have been 5 and 8 times higher than those of the concentrations of WSON in aerosol and rain, respectively. Table 1 shows the number of negative WSON values and the positive WSON biases for coarse and fine modes.…”

“…Based on molar N / P ratios in the atmospheric input (order of magnitude higher than that of Redfield; Markaki et al, 2003Markaki et al, , 2010Koçak et al, 2010) and riverine fluxes (at least 1.8 times larger than that of Redfield; Ludwig et al, 2009;Koçak et al, 2010) it has been suggested that the eastern Mediterranean receives excessive amounts of dissolved inorganic nitrogen and that this unbalanced input may result in even more phosphorus deficiency (Ludwig et al, 2009;Koçak et al, 2010), whilst the atmospheric deposition of reactive nitrogen may cause accumulation of nitrogen in the water column (Jickells et al, 2017). Very little research has focused on the importance of water-soluble organic nitrogen input to marine productivity in the eastern Mediterranean (Mace et al, 2003a;. Hence, the unique contributions of the current study will be to (i) define the temporal variability of atmospheric water-soluble organic nitrogen, (ii) assign the origin of the water-soluble organic nitrogen, (iii) assess the influence of mineral dust on water-soluble organic nitrogen and (iv) enhance our knowledge of the quantitative dry and wet deposition of water-soluble organic nitrogen and its possible influence on marine productivity in the northeastern Mediterranean.…”