Lise Lotte Sørensen

Impacts of Atmospheric Anthropogenic Nitrogen on the Open Ocean

Increasing quantities of atmospheric anthropogenic fixed nitrogen entering the open ocean could account for up to about a third of the oceans external (nonrecycled) nitrogen supply and up to ∼3% of the annual new marine biological production, ∼0.3 petagram of carbon per year. This input could account for the production of up to ∼1.6 teragrams of nitrous oxide (N2O) per year. Although ∼10% of the oceans drawdown of atmospheric anthropogenic carbon dioxide may result from this atmospheric nitrogen fertilization, leading to a decrease in radiative forcing, up to about two-thirds of this amount may be offset by the increase in N2O emissions. The effects of increasing atmospheric nitrogen deposition are expected to continue to grow in the future.

Air–sea flux of CO2 in arctic coastal waters influenced by glacial melt water and sea ice

Annual air–sea exchange of CO2 inYoung Sound,NEGreenlandwas estimated using pCO2 surface-water measurements during summer (2006–2009) and during an ice-covered winter 2008. All surface pCO2 values were below atmospheric levels indicating an uptake of atmospheric CO2. During sea ice formation, dissolved inorganic carbon (DIC) content is reduced causing sea ice to be under saturated in CO2. Approximately 1% of the DIC forced out of growing sea ice was released into the atmosphere while the remaining 99% was exported to the underlying water column. Sea ice covered the fjord 9 months a year and thereby efficiently blocked air–sea CO2 exchange. During sea ice melt, dissolution of CaCO3 combined with primary production and strong stratification of the water column acted to lower surface-water pCO2 levels in the fjord. Also, a large input of glacial melt water containing geochemically reactive carbonate minerals may contribute to the low surface-water pCO2 levels. The average annual uptake of atmospheric CO2 was estimated at 2.7 mol CO2 m−2 yr−1 or 32 g C m−2 yr−1 for the study area, which is lower than estimates from the Greenland Sea. Variability in duration of sea ice cover caused significant year-to-year variation in annual gas exchange.

Fluxes of ammonia in the coastal marine boundary layer

Abstract Concentrations of ammonia in air and ammonium in surface water were measured from a platform in the Southern North Sea close to the Dutch coast. Fluxes were derived from the measurements applying Monin–Obukhov similarity theory and exchange velocities calculated. The fluxes and air concentrations of ammonia were compared to results obtained from the Lagrangian transport-chemistry model ACDEP with and without a parameterisation of outgoing fluxes of ammonia from the sea. The results indicate that the flux may in fact be upward during periods with low atmospheric ammonia concentrations and that the calculated overall ammonia dry deposition may be overestimated by a factor two or more in the coastal region. A more detailed study is needed in order to quantify how this may influence overall deposition to given marine waters. In some cases the deposition may solely be redistributed whereas the total deposition is only marginally influenced.

Diffusion scrubber technique used for measurements of atmospheric ammonia

Abstract A diffusion scrubber (DS) was developed to measure trace levels of gaseous ammonia in ambient air. The sampling resolution time for this method is 10 min and the detection limit is estimated to be 0.01 ppbv. The response to the NI-I3 concentrations is found to be dependent on the relative humidity in the ambient air and the temperature. The method is calibrated by using a diluted NH3 cylinder gas, and the concentrations of the calibration gas were in the range 0.02–2 ppbv during the test. Sampling performed with the DS-method is compared to sampling performed by a filter pack and a continuous flow denuder (AMANDA). The DS-method shows good agreement with the continuous flow denuder and the filter pack.

ATMOSPHERIC NITROGEN INPUT TO THE KATTEGAT

Abstract An overview is given of the processes involved in the atmospheric deposition of nitrogen compounds. These processes are incorporated in an atmospheric transport model that is used to calculate the nitrogen input to the Kattegat, the sea area between Denmark and Sweden. The model results show that the total atmospheric nitrogen input to the Kattegat is approximately 960 kg N km2 yr1. The nitrogen input to the Kattegat is dominated by the wet depositions of NHx (42%) and NOy (30%). The contribution from the dry deposition of NHx is 17% and that of the dry deposition of NOy is 11 %. The contribution of the atmospheric input of nitrogen to the Kattegat is about 30% of the total input including the net transport from other sea areas, runoff etc.

Characterization of humic-like substances in Arctic aerosols

Humic-like substances (HULIS) are a complex group of relatively high molecular weight organic compounds which contribute considerably to the mass of organic carbon (OC) and influence the light-absorbing properties of aerosols. In this work, HULIS were investigated for the first time in the high-Arctic atmosphere, focusing on the chemical characterization and mass contribution of HULIS to the total suspended particle (TSP) mass using weekly aerosol samples collected at Station Nord, northeast Greenland every fourth week during 2010. Average HULIS-C concentration was 11 ng C m−3 during the darker months (November–April) and 4 ng C m−3 during the other months (May–October) with an annual mass concentration of 0.02 ± 0.01 µg m−3. HULIS-C contributed to 3–16% of water-soluble organic carbon (WSOC), whereas HULIS accounted for 0.7–4.1% of TSP mass, with TSP typically below 1.0 µg m−3. Concentrations of OC, WSOC, HULIS, selected HULIS functional groups (carboxylic acids, aromatic carboxylic acids, and organosulfates) and levoglucosan overlapped with the typical Arctic haze pattern with elevated concentrations during winter to early spring. The aromatic carboxylic acid portion accounted for a larger share of total carboxylic acid of HULIS during the darker months (7%) compared to the brighter months (3%). The more abundant aromatic carboxylic acid functional groups and the moderate correlation between HULIS and levoglucosan concentrations during the darker months both indicate that biomass burning aerosols and thereby emissions of aromatic compounds could contribute to HULIS in the Arctic, especially during late winter. During the brighter months, relatively higher average molecular weight of HULIS was observed.

Dry deposition of reactive nitrogen to marine environments: recent advances and remaining uncertainties.

Many highly productive marine ecosystems exhibit nitrogen limitation or co-limitation. This article is a status review of research into the exchange of nitrogen between the atmosphere and these ecosystems with a particular focus on reactive nitrogen compounds. A summary of research conducted over the past ten years is presented and a perspective given as to remaining uncertainities and research needs. Looking toward development of coastal management modeling tools, we illustrate the processes that need to be resolved in order to accurately simulate the flux from the atmosphere and provide guidance on the required resolution of such models.

Flux divergence of nitric acid in the marine atmospheric surface layer

It is hypothesized that removal of HNO3 from the atmosphere close to the sea surface is due to two processes: dry deposition to the sea surface and chemical reaction with sea spray. The latter process invalidates the application of the constant flux layer assumption to calculate dry deposition based on concentrations of HNO3 at, e.g., a reference height of 10 m. A field experiment was carried out to investigate this hypothesis, and the measured concentration profiles were found to differ dramatically from the log linear profiles, which would have been produced by turbulent transport only. Surface fluxes of HNO3 were calculated from the measured profiles taking chemical reactions into account and were compared to surface fluxes calculated by the traditional resistance method. It was found that the surface fluxes could be a factor of two less when chemical reactions are taken into account, depending on the characteristics of the near-surface aerosols. HNO3 loss rates due to heterogeneous chemistry are calculated by two independent methods and are compared.

Air–Sea \(\mathrm{CO}_{2}\) Gas Transfer Velocity in a Shallow Estuary

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