Measurements and modeling of reactive nitrogen deposition in southeast Brazil

Increased reactive nitrogen (N_r) deposition due to expansion of agro-industry was investigated considering emission sources, atmospheric transport and chemical reactions. Measurements of the main inorganic nitrogen species (NO₂, NH₃, HNO₃, and aerosol nitrate and ammonium) were made over a period of one year at six sites distributed across an area of ∼130,000 km² in southeast Brazil. Oxidized species were estimated to account for ∼90% of dry deposited N_r, due to the region’s large emissions of nitrogen oxides from biomass burning and road transport. NO₂-N was important closer to urban areas, however overall HNO₃-N represented the largest component of dry deposited N_r. A simple mathematical modeling procedure was developed to enable estimates of total N_r dry deposition to be made from knowledge of NO₂ concentrations. The technique, whose accuracy here ranged from <1% to 29%, provides a useful new tool for the mapping of reactive nitrogen deposition.     

Deposition of reactive nitrogen during the Rocky Mountain Airborne Nitrogen and Sulfur (RoMANS) study

Increases in reactive nitrogen deposition are a growing concern in the U.S. Rocky Mountain west. The Rocky Mountain Airborne Nitrogen and Sulfur (RoMANS) study was designed to improve understanding of the species and pathways that contribute to nitrogen deposition in Rocky Mountain National Park (RMNP). During two 5-week field campaigns in spring and summer of 2006, the largest contributor to reactive nitrogen deposition in RMNP was found to be wet deposition of ammonium (34% spring and summer), followed by wet deposition of nitrate (24% spring, 28% summer). The third and fourth most important reactive nitrogen deposition pathways were found to be wet deposition of organic nitrogen (17%, 12%) and dry deposition of ammonia (14%, 16%), neither of which is routinely measured by air quality/deposition networks operating in the region. Total reactive nitrogen deposition during the spring campaign was determined to be 0.45 kg ha⁻¹ and more than doubled to 0.95 kg ha⁻¹ during the summer campaign.     

Low cost measurements of nitrogen and sulphur dry deposition velocities at a semi-alpine site: gradient measurements and a comparison with deposition model estimates

The conditional time averaged gradient method was used to measure air-surface exchange of nitrogen and sulphur compounds at a semi-alpine site in Southern Norway. Dry deposition velocities were then obtained from the bi-weekly concentration gradient measurements. Annual deposition velocities were found to be 1.4, 11.8 and 4.0 mm s(-1) for NH3, HNO3 and SO2, respectively, if all data were included, and to be 10.8, 11.8 and 13.0 mm s(-1), respectively, if only positive values were included. Measured deposition velocities were compared to two sets of values estimated from a big-leaf dry deposition module applying to two different land types (short grass and forbs, and tundra), driven by measured micrometeorological parameters. The deposition module gives reasonable values for this site throughout the year, but does not reproduce the large variability as shown in the measured data. No apparent seasonal variations were found from either measurements or module estimates due to the very low productivity of the studied area.     

Description and evaluation of a model of deposition velocities for routine estimates of air pollutant dry deposition over North America.: Part I: model development

This paper describes the development of a detailed dry deposition model for routine computation of dry deposition velocities of SO₂, O₃, HNO₃ and fine particle SO₄²⁻ across much of North America. Four different dry deposition/surface exchange sub-models have been combined with the current Canadian weather forecast model (Global Environmental Multiscale model) with a 3 h time resolution and a horizontal spatial resolution of 35 km. The present model uses the US Geological Survey North American Land Cover Characteristics data to obtain fourteen different land use and five seasonal categories. The four sub-models used are a multi-layer model for gaseous species over taller canopy land-use types, a big-leaf model for gaseous species over lower canopies (including bare soil and water) and for HNO₃ under all surface types and, two different models for SO₄²⁻, one for tall canopies and the other for short canopies. All necessary parameters for each sub-model, chemical species, land-use and seasonal categories have been selected from available data libraries or from the values reported in the literature. The purpose for developing this model (referred to as the Routine Deposition Model (RDM)), when coupled with air concentration data, is to provide estimates of seasonal dry deposition, which can be combined with wet deposition to produce total deposition estimates. Model theory is discussed in this paper and model sensitivity tests and results will be presented in a companion paper.     

The impact of nitrogen deposition on acid grasslands in the Atlantic region of Europe

A survey of 153 acid grasslands from the Atlantic biogeographic region of Europe indicates that chronic nitrogen deposition is changing plant species composition and soil and plant-tissue chemistry. Across the deposition gradient (2-44 kg N ha⁻¹ yr⁻¹) grass richness as a proportion of total species richness increased whereas forb richness decreased. Soil C:N ratio increased, but soil extractable nitrate and ammonium concentrations did not show any relationship with nitrogen deposition. The above-ground tissue nitrogen contents of three plant species were examined: Agrostis capillaris (grass), Galium saxatile (forb) and Rhytidiadelphus squarrosus (bryophyte). The tissue nitrogen content of neither vascular plant species showed any relationship with nitrogen deposition, but there was a weak positive relationship between R. squarrosus nitrogen content and nitrogen deposition. None of the species showed strong relationships between above-ground tissue N:P or C:N and nitrogen deposition, indicating that they are not good indicators of deposition rate.     

Description and evaluation of a model of deposition velocities for routine estimates of dry deposition over North America. Part II: review of past measurements and model results

Numerical sensitivity tests and four months of complete model runs have been conducted for the Routine Deposition Model (RDM). The influence of individual model inputs on dry deposition velocity as a function of land-use category (LUC) and pollutant (SO₂, O₃, SO²⁻₄ and HNO₃) were examined over a realistic range of values for solar radiation, stability and wind speed. Spatial and temporal variations in RDM deposition velocity (V_d) during June – September 1996 time period generated using meteorological input from a mesoscale model run at 35 km resolution over north-eastern North America were also examined. Comparison of RDM V_d values to a variety of measurements of dry deposition velocities of SO₂, O₃, SO²⁻₄ and NHO₃ that have been reported in the literature demonstrated that RDM produces realistic results. Over northeastern NA RDM monthly averaged dry deposition velocities for SO₂ vary from 0.2 to 3.0 cm s⁻¹ with the highest deposition velocities over water surfaces. For O₃, the monthly averaged dry deposition velocities are from 0.05 to 1.0 cm s⁻¹ with the lowest values over water surfaces and the highest over forested areas. For HNO₃, the monthly averaged dry deposition velocities have the range of 0.5 to 6 cm s⁻¹, with the highest values for forested areas. For SO²⁻₄, they range from 0.05–1.5 cm s⁻¹, with the lowest values over water and the highest over forest. The monthly averaged dry deposition velocities for SO₂ and O₃ are higher in the growing season compared to the fall, but this behaviour is not apparent for HNO₃ and sulphate. In the daytime, the hourly averaged dry deposition velocities for SO₂, O₃, SO²⁻₄ and HNO₃ are higher than that in the nighttime over most of the vegetated area. The diurnal variation is most evident for surfaces with large values for leaf area index (LAI), such as forests. Based on the results presented in this paper, it is concluded that RDM V_d values can be combined with measured air concentrations over hourly, daily or weekly periods to determine dry deposition amounts and with wet deposition measurements to provide seasonal estimates of total deposition and estimates of the relative importance of dry deposition.     

Lichen-based critical loads for atmospheric nitrogen deposition in Western Oregon and Washington Forests, USA

Critical loads (CLs) define maximum atmospheric deposition levels apparently preventative of ecosystem harm. We present first nitrogen CLs for northwestern North America’s maritime forests. Using multiple linear regression, we related epiphytic-macrolichen community composition to: 1) wet deposition from the National Atmospheric Deposition Program, 2) wet, dry, and total N deposition from the Communities Multi-Scale Air Quality model, and 3) ambient particulate N from Interagency Monitoring of Protected Visual Environments (IMPROVE). Sensitive species declines of 20-40% were associated with CLs of 1-4 and 3-9 kg N ha⁻¹ y⁻¹ in wet and total deposition. CLs increased with precipitation across the landscape, presumably from dilution or leaching of depositional N. Tight linear correlation between lichen and IMPROVE data suggests a simple screening tool for CL exceedance in US Class I areas. The total N model replicated several US and European lichen CLs and may therefore be helpful in estimating other temperate-forest lichen CLs.     

Nitrogen deposition and its ecological impact in China: An overview

Nitrogen (N) deposition is an important component in the global N cycle that has induced large impacts on the health and services of terrestrial and aquatic ecosystems worldwide. Anthropogenic reactive N (N_r) emissions to the atmosphere have increased dramatically in China due to rapid agricultural, industrial and urban development. Therefore increasing N deposition in China and its ecological impacts are of great concern since the 1980s. This paper synthesizes the data from various published papers to assess the status of the anthropogenic N_r emissions and N deposition as well as their impacts on different ecosystems, including empirical critical loads for different ecosystems. Research challenges and policy implications on atmospheric N pollution and deposition are also discussed. China urgently needs to establish national networks for N deposition monitoring and cross-site N addition experiments in grasslands, forests and aquatic ecosystems. Critical loads and modeling tools will be further used in N_r regulation.     

Comparison of annual dry and wet deposition fluxes of selected pesticides in Strasbourg, France

This work summarizes the results of a study of atmospheric wet and dry deposition fluxes of Deisopropyl-atrazine (DEA), Desethyl-atrazine (DET), Atrazine, Terbuthylazine, Alachlor, Metolachlor, Diflufenican, Fenoxaprop-p-ethyl, Iprodione, Isoproturon and Cymoxanil pesticides conducted in Strasbourg, France, from August 2000 through August 2001. The primary objective of this work was to calculate the total atmospheric pesticide deposition fluxes induced by atmospheric particles. To do this, a modified one-dimensional cloud water deposition model was used. All precipitation and deposition samples were collected at an urban forested park environment setting away from any direct point pesticide sources. The obtained deposition fluxes induced by atmospheric particles over a forested area showed that the dry deposition flux strongly contributes to the total deposition flux. The dry particle deposition fluxes are shown to contribute from 4% (DET) to 60% (cymoxanil) to the total deposition flux (wet + dry).     

华北地区温度和风速对冬季灰霾形成的潜在影响

针对华北地区灰霾日渐严重的问题,利用1973—2012年地面气象观测数据,从冬季采暖耗能排污和平均风速变化的角度,结合Mann-Kendall法分析了气候变化背景下华北冬季灰霾相关气象因素的长时间尺度演化规律。研究表明,华北大部地区冬季平均风速明显下降,影响大气污染物稀释扩散,容易积累高浓度污染,有助于抬升灰霾发生的频率和强度;除个别地区受气候变化引发极寒事件影响、采暖度日变化趋势持平外,华北各地受长时间尺度上气候变化所致冬季增温效应影响,采暖日和采暖度日整体呈下降趋势,采暖耗能排污减少,有利于降低粉尘污染排放。因华北地区统一采用固定120 d时限的供暖制度,采暖日和采暖度日的下降并没有转化为采暖耗能排污的下降,个别城市采暖度日甚至有所上升。因华北南部及沿海站点计算得到的采暖日明显低于120 d,在这些城市根据天气条件试行灵活供暖,可能明显降低冬季采暖耗能排污,有助于消解雾霾。     

东部平原湖区沉积物中溶解性有机氮分布特征

选择东部平原湖区11个湖泊进行水质和表层沉积物调查,采用综合营养状态指数（TLI）对各湖泊营养状态进行评价,研究了沉积物溶解性有机氮（DON）和游离氨基酸（FAA）的含量分布及DON分子质量分级特征,并探讨了不同湖泊沉积物有机质来源。结果表明：除固城湖和骆马湖处于中营养水平外,东部平原湖区其他湖泊均处于富营养化状态。沉积物DON浓度差异较大,在9.98~182.00 mg·kg-1之间波动,均值为57.25 mg·kg-1,太湖、滆湖、阳澄湖沉积物DON含量较高,均在140 mg·kg-1以上,其他湖泊沉积物DON含量均在50 mg·kg-1以下。区域内氨基酸（FAA）分布比较均匀,FAA浓度在3.58~13.28 mg·kg-1之间,平均值是8.14 mg·kg-1。沉积物DON和FAA含量与沉积物其他形态氮、溶解性有机碳（DOC）等污染指标均表现出显著正相关性。东部平原湖区沉积物分子质量分级结果表明：该湖区沉积物DON、DOC和SUV254基本都分布在 30 kDa 2个范围内。东部平原湖区C/N比的值介于2.31~89.02之间,除滆湖外其他湖泊沉积物C/N值均大于10,说明该地区湖泊沉积物有机质主要来自外源。     

Concentration, size distribution, and dry deposition rate of particle-associated metals in the Los Angeles region

Daily averaged atmospheric concentrations and dry deposition fluxes of particulate metals were measured seasonally at six urban sites and one non-urban coastal site in the Los Angeles region using a conventional total suspended particulate matter (TSP) filter, surrogate surface deposition plates, and a Noll Rotary Impactor (NRI), which provides information about particle size distribution in four size ranges above 6 μm. With the exception of the non-urban site, particulate metal concentrations and deposition fluxes were remarkably uniform spatially and temporally. At all sites there were significant metal concentrations on particles greater than 10 μm, a commonly used upper limit for many air quality monitoring studies, and these large particles were estimated to be responsible for most of the deposited mass of metals. Annual averaged values of deposition rates measured with a surrogate surface were in good agreement with values estimated using theoretical deposition velocities in conjunction with measured size-segregated particle concentrations. Image analysis of particles deposited on NRI stage A, which collects all particles greater than 6 μm, indicated nighttime metal concentrations and deposition at the non-urban coastal site was higher than in the day time due to offshore advection of urban air associated with the diurnal land breeze. Measured enrichments of crustal elements and metals were correlated, indicating efficient mixing of natural and anthropogenic material from different sources, hypothesized to be the result of cyclical resuspension and deposition of dust by moving vehicles and wind.     

Atmospheric deposition, retention, and stream export of dioxins and PCBs in a pristine boreal catchment

The mass-balance between diffuse atmospheric deposition of organic pollutants, amount of pollutants retained by the terrestrial environment, and levels of pollutants released to surface stream waters was studied in a pristine northern boreal catchment. This was done by comparing the input of atmospheric deposition of polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) and PCBs with the amounts exported to surface waters. Two types of deposition samplers were used, equipped with a glass fibre thimble and an Amberlite sampler respectively. The measured fluxes showed clear seasonality, with most of the input and export occurring during winter and spring flood, respectively. The mass balance calculations indicates that the boreal landscape is an effective sink for PCDD/Fs and PCBs, as 96.0-99.9 % of received bulk deposition was retained, suggesting that organic pollutants will continue to impact stream water in the region for an extended period of time.     

Nitrogen concentrations in mosses indicate the spatial distribution of atmospheric nitrogen deposition in Europe

In 2005/6, nearly 3000 moss samples from (semi-)natural location across 16 European countries were collected for nitrogen analysis. The lowest total nitrogen concentrations in mosses (<0.8%) were observed in northern Finland and northern UK. The highest concentrations (≥1.6%) were found in parts of Belgium, France, Germany, Slovakia, Slovenia and Bulgaria. The asymptotic relationship between the nitrogen concentrations in mosses and EMEP modelled nitrogen deposition (averaged per 50 km × 50 km grid) across Europe showed less scatter when there were at least five moss sampling sites per grid. Factors potentially contributing to the scatter are discussed. In Switzerland, a strong (r² = 0.91) linear relationship was found between the total nitrogen concentration in mosses and measured site-specific bulk nitrogen deposition rates. The total nitrogen concentrations in mosses complement deposition measurements, helping to identify areas in Europe at risk from high nitrogen deposition at a high spatial resolution.     

Seasonal and spatial occurrence and distribution of atmospheric polycyclic aromatic hydrocarbons (PAHs) in rural and urban areas of the North Chinese Plain

Passive air sampling (PAS) was employed to study the occurrence of gaseous and particle-bound PAHs in the North Chinese Plain. The averaged concentrations of gaseous and particle-bound PAHs were 485 ± 209 ng/m³ and 267 ± 161 ng/m³, respectively. The PAHs concentrations at urban sites were generally higher than those at rural ones with ratios <1.5 in spring, summer and fall, but differences between them were not significant for the wintertime and annually averaged concentrations. This urban-rural distribution pattern was related to the PAHs emission sources. PAHs spatial variation can be partially (49%) explained by emission with a simple linear regression method. Both the gaseous and particle-bound PAHs were highest in winter and lowest in summer, with winter/summer ratios of 1.8 and 8, respectively. Emission strength was the most important factor for the seasonality.     

Elevated atmospheric deposition and dynamics of mercury in a remote upland forest of southwestern China

Mt. Gongga area in southwest China was impacted by Hg emissions from industrial activities and coal combustion, and annual means of atmospheric TGM and PHg concentrations at a regional background station were 3.98 ng m⁻³ and 30.7 pg m⁻³, respectively. This work presents a mass balance study of Hg in an upland forest in this area. Atmospheric deposition was highly elevated in the study area, with the annual mean THg deposition flux of 92.5 μg m⁻² yr⁻¹. Total deposition was dominated by dry deposition (71.8%), and wet deposition accounted for the remaining 28.2%. Forest was a large pool of atmospheric Hg, and nearly 76% of the atmospheric input was stored in forest soil. Volatilization and stream outflow were identified as the two major pathways for THg losses from the forest, which yielded mean output fluxes of 14.0 and 8.6 μg m⁻² yr⁻¹, respectively.     

Historical nitrogen content of bryophyte tissue as an indicator of increased nitrogen deposition in the Cape Metropolitan Area, South Africa

Information on changes in precipitation chemistry in the rapidly expanding Cape Metropolitan Area (CMA) of South Africa is scarce. To obtain a long-term record of N deposition we investigated changes in moss foliar N, C:N ratios and nitrogen isotope values that might reflect precipitation chemistry. Tissue from 9 species was obtained from herbarium specimens collected between 1875 and 2000 while field samples were collected in 2001/2002. There is a strong trend of increasing foliar N content in all mosses collected over the past century (1.32-1.69 %N). Differences exist between ectohydric mosses which have higher foliar N than the mixohydric group. C:N ratios declined while foliar δ¹⁵N values showed no distinct pattern. From relationships between moss tissue N and N deposition rates we estimated an increase of 6-13 kg N ha⁻¹ a⁻¹ since 1950. Enhanced N deposition rates of this magnitude could lead to biodiversity losses in native ecosystems.     

Bioaccumulation behaviour of transplants of the lichen Flavoparmelia caperata in relation to total deposition at a polluted location in Portugal

This experiment compares the short and long time element accumulation behaviour of transplants of Flavoparmelia caperata lichen thalli and total deposition in an atmospheric polluted area. It was found that lichens exposed for a short time behaved differently from lichens in cumulative exposition suggesting the presence of acclimatization behaviour. The lichen transplant elemental content does not unequivocally represent the average or cumulative environmental availability of the exposure period. Reflection characteristics depend on the element and the lichen physiological conditions. Good correlations between lichen elemental contents and total deposition were obtained when a physiological lichen parameter was introduced in a mathematical model, suggesting that metabolically mediated accumulation is important.     

Generation of reactive oxygen species in cyanobacteria and green algae induced by allelochemicals of submerged macrophytes

Inhibition of phytoplankton by allelochemicals released by submerged macrophytes is reported to be one of the mechanisms that maintain a clear-water state in shallow lakes. In order to elucidate this mechanism, the ability of six polyphenols and two long-chain fatty acids to induce the generation of reactive oxygen species (ROS) in phytoplankton was studied using the ROS sensitive probe 2′,7′- dichlorodihydrofluorescein diacetate (DCFH-DA). The results showed that only (+)-catechin (CA) and pyrogallic acid (PA) could induce ROS formation in Microcystis aeruginosa and Pseudokirchneriella subcapitata. 25 mg L⁻¹ CA caused 1.2, 1.4 and 1.8 times increase of ROS levels in M. aeruginosa at 1, 2 and 4 h exposure, respectively, and, correspondingly in P. subcapitata cells, these values were 3.7, 6.2 and 7.7, respectively. PA also significantly increased the levels of intracellular ROS in P. subcapitata (P < 0.01); however, significant ROS generation in M. aeruginosa was observed at only 4 h exposure (P < 0.01). Light enhanced ROS generation in CA treated cells, but not in the cells treated with PA. CA and PA may act as redox cyclers after uptake by test organisms and produce ROS successively. These results suggest that the oxidative stress induced by the redox cycling property of allelochemicals may be one of the important causes for the inhibitory effect of some submerged macrophytes towards undesired phytoplankton in natural aquatic ecosystems.     

Spatial distribution and source identification of wet deposition at remote EANET sites in Japan

Wet deposition of major ions was discussed from the viewpoint of its potential sources for six remote EANET sites in Japan (Rishiri, Happo, Oki, Ogasawara, Yusuhara, and Hedo) having sufficiently high data completeness during 2000–2004. The annual deposition for each site ranged from 12.1 to 46.6 meq m⁻² yr⁻¹ for nss-SO₄²⁻, from 5.0 to 21.9 meq m⁻² yr⁻¹ for NO₃⁻. The ranges of annual deposition of the two ions for the sites were lower than those for urban and rural sites in Japanese Acid Deposition Survey by Ministry of the Environment, Japan, and higher than those for global remote marine sites. Factor analysis was performed on log-transformed daily wet deposition of major ions for each site. The obtained two factors were interpreted as (1) acid and soil source (or acid source for some sites), and (2) sea-salt source for all the sites. This indicates that wet deposition of ions over the remote areas in Japan has a similar structure in terms of types of sources. Factor scores of acid and soil source were relatively high during Kosa (Asian dust) events in spring in western Japan. Back-trajectories for high-deposition episodes of acid and soil source (or acid source) for the remote sites showed that episodic air masses frequently came from the northeastern area of Asian Continent in spring and winter, and from central China in summer and autumn. This indicates a large contribution of continental emissions to wet deposition of ions over the remote areas in Japan.