Source contribution to the bulk atmospheric deposition of minor and trace elements in a Northern Spanish coastal urban area

Mo, Ni, Pb, Ti, V and Zn was investigated in Santander, a Northern Spanish coastal city. Bulk deposition samples were collected monthly for three years using a bottle/funnel device. Taking into account that heavy metals are bioavailable only in their soluble forms, water-soluble and water-insoluble fractions were evaluated separately for element concentration. The fluxes of the studied elements in the bulk deposition exhibited the following order: Zn>Mn>>Cu>Cr>Pb>V>Ni>>As>Mo>Cd. The fluxes of Zn and Mn were more than 10 times higher than those of the other elements, withmaximumvalues of 554.5 and 334.1 µg m-2 day-1, respectively. Low solubilities (below 22%) were found for Cr, Ti and Pb, whereas the highest solubility was found for Zn (78%). With the exception of Cu, all of the studied metals in the water-soluble fraction of the atmospheric deposition showed seasonal dependence, due to the seasonal variability of precipitation. The enrichment factors (EFs) of Cu, Cd and Zn were higher than 100, indicating a clear anthropogenic origin. The EF of Mn (50) was below 100, but an exclusively industrial origin is suggested. Positive Matrix Factorisation (PMF) was used for the source apportionment of the studiedminor and trace elements in the soluble fraction. Four factors were identified from PMF, and their chemical profiles were compared with those calculated from known sources that were previously identified in Santander Bay: two industrial sources, the first of which was characterised by Zn and Mn, which contributes 62.5% of the total deposition flux of the studied elements; a traffic source; and a maritime source. Zinc and Mn are considered to be the most characteristic pollutants of the studied area.The authors are grateful for the financial support from the CTM 2010-16068 project (Spanish Ministry of Science and Innovation)

Ammonia deposition near hot spots: processes, models and monitoring methods

Atmospheric reduced nitrogen (NHx) mainly originates from hot spots, which can be considered as intensive area or point sources. A large fraction of the emitted NHx may be recaptured by the surrounding vegetation, hence reducing the contribution of these hot spots to long-range transport of NHx. This paper reviews the processes leading to local recapture of NHx near hot spots as well as existing models and monitoring methods. The existing models range from research models to more operational models that can be coupled with long-range transport model provided the necessary information on emissions is available. Local recapture of NH3 ranges from 2% to 60% within 2 km of a hot-spot and it is sensitive to source height, atmospheric stability, wind speed, structure of the surrounding canopies, as well as stomatal absorption, which mainly depends on green leaf area index and stomatal NH3 compensation point of vegetation, and finally, cuticular deposition, which depends primarily on vegetation wetness. The main uncertainties and limitations on NHx recapture models and monitoring techniques are discussed

Practical considerations for addressing uncertainties in monitoring bulk deposition

The assessment of the deposition of both wet (rain and cloud) and dry sedimenting particles is a prerequisite for estimating element fluxes in ecosystem research. Many nations and institutions operate deposition networks using different types of sampler. However, these samplers have rarely been characterized with respect to their sink properties. Major errors in assessing bulk deposition can result from poor sampling properties and defective sampling strategies. Relevant properties are: sampler geometry and material, in particular the shape of the rim; sink properties for gases and aerosols; and microbial transformations of the collected samples. An adequate number of replicates allows the identification of samples which are contaminated, in particular by bird droppings. The paper discusses physical and chemical properties of the samplers themselves. The dependence of measurement accuracy on the number of replicates and the sampling area exposed is discussed. Recommendations are given for sampling strategies, and for making corrections and substitution of missing data. Recommendations are given for sampling strategies and for making corrections and substitution of missing data

Aerosol fluxes and particle growth above managed grassland

Particle deposition velocities (11–3000 nm diameter) measured above grassland by eddy covariance during the EU GRAMINAE experiment in June 2000 averaged 0.24 and 0.03 mm s−1 to long (0.75 m) and short (0.07 m) grass, respectively. After fertilisation with 108 kg N ha−1 as calcium ammonium nitrate, sustained apparent upward fluxes of particles were observed. Analysis of concentrations and fluxes of potential precursor gases, including NH3, HNO3, HCl and selected VOCs, shows that condensation of HNO3 and NH3 on the surface of existing particles is responsible for this effect. A novel approach is developed to derive particle growth rates at the field scale, from a combination of measurements of vertical fluxes and particle size-distributions. For the first 9 days after fertilization, growth rates of 11 nm particles of 7.04 nm hr−1 and 1.68 nm hr−1 were derived for day and night-time conditions, respectively. This implies total NH4NO3 production rates of 1.11 and 0.44 μg m−3 h−1, respectively. The effect translates into a small error in measured ammonia fluxes (0.06% day, 0.56% night) and a large error in NH4+ and NO3− aerosol fluxes of 3.6% and 10%, respectively. By converting rapidly exchanged NH3 and HNO3 into slowly depositing NH4NO3, the reaction modifies the total N budget, though this effect is small (<1% for the 10 days following fertilization), as NH3 emission dominates the net flux. It is estimated that 3.8% of the fertilizer N was volatilised as NH3, of which 0.05% re-condensed to form NH4NO3 particles within the lowest 2 m of the surface layer. This surface induced process would at least scale up to a global NH4NO3 formation of ca. 0.21 kt N yr−1 from NH4NO3 fertilisers and potentially 45 kt N yr−1 from NH3 emissions in general. [Abstract from: http://www.biogeosciences.net/6/1627/2009/bg-6-1627-2009.html

An integrated tool to assess the role of new planting in PM10 capture and the human health benefits: a case study in London.

The role of vegetation in mitigating the effects of PM(10) pollution has been highlighted as one potential benefit of urban greenspace. An integrated modelling approach is presented which utilises air dispersion (ADMS-Urban) and particulate interception (UFORE) to predict the PM(10) concentrations both before and after greenspace establishment, using a 10 x 10 km area of East London Green Grid (ELGG) as a case study. The corresponding health benefits, in terms of premature mortality and respiratory hospital admissions, as a result of the reduced exposure of the local population are also modelled. PM(10) capture from the scenario comprising 75% grassland, 20% sycamore maple (Acer pseudoplatanus L.) and 5% Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) was estimated to be 90.41 t yr(-1), equating to 0.009 t ha(-1) yr(-1) over the whole study area. The human health modelling estimated that 2 deaths and 2 hospital admissions would be averted per year

Comparison of models used for national agricultural ammonia emission inventories in Europe: Litter-based manure systems

Six N-flow models, used to calculate national ammonia (NH3) emissions from agriculture in different European countries, were compared using standard data sets. Scenarios for litter-based systems were run separately for beef cattle and for broilers, with three different levels of model standardisation: (a) standardized inputs to all models (FF scenario); (b) standard N excretion, but national values for emission factors (EFs) (FN scenario); (c) national values for N excretion and EFs (NN scenario). Results of the FF scenario for beef cattle produced very similar estimates of total losses of total ammoniacal-N (TAN) (±6% of the mean total), but large differences in NH3 emissions (±24% of the mean). These differences arose from the different approaches to TAN immobilization in litter, other N losses and mineralization in the models. As a result of those differences estimates of TAN available at spreading differed by a factor of almost 3. Results of the FF scenario for broilers produced a range of estimates of total changes in TAN (±9% of the mean total), and larger differences in the estimate of NH3 emissions (±17% of the mean). The different approaches among the models to TAN immobilization, other N losses and mineralization, produced estimates of TAN available at spreading which differed by a factor of almost 1.7. The differences in estimates of NH3 emissions decreased as estimates of immobilization and other N losses increased. Since immobilization and denitrification depend also on the C:N ratio in manure, there would be advantages to include C flows in mass-flow models. This would also provide an integrated model for the estimation of emissions of methane, non-methane VOCs and carbon dioxide. Estimation of these would also enable an estimate of mass loss, calculation of the N and TAN concentrations in litter-based manures and further validation of model output

Monitoring and modelling of biosphere/atmosphere exchange of gases and aerosols in Europe

Monitoring and modelling of deposition of air pollutants is essential to develop and evaluate policies to abate the effects related to air pollution and to determine the losses of pollutants from the atmosphere. Techniques for monitoring wet deposition fluxes are widely applied. A recent intercomparison experiment, however, showed that the uncertainty in wet deposition is relatively high, up to 40%, apart from the fact that most samplers are biased because of a dry deposition contribution. Wet deposition amounts to about 80% of the total deposition in Europe with a range of 10–90% and uncertainty should therefore be decreased. During recent years the monitoring of dry deposition has become possible. Three sites have been operational for 5 years. The data are useful for model development, but also for model evaluation and monitoring of progress in policy. Data show a decline in SO2 dry deposition, whereas nitrogen deposition remained constant. Furthermore, surface affinities for pollutants changed leading to changes in deposition. Deposition models have been further developed and tested with dry deposition measurements and total deposition measurements on forests as derived from throughfall data. The comparison is reasonable given the measurement uncertainties. Progress in ozone surface exchange modelling and monitoring shows that stomatal uptake can be quantified with reasonable accuracy, but external surface uptake yields highest uncertaint