Total Dry Deposition Research Articles

Measured black carbon deposition over the central Himalayan glaciers: Concentrations in surface snow and impact on snow albedo reduction

Deposition of ambient black carbon (BC) aerosols over snow-covered areas reduces surface albedo and accelerates snowmelt. Based on in-situ atmospheric BC data and the WRF-Chem model, we estimated the dry and wet deposition of BC over the Yala glacier of the central Himalayan region in Nepal during 2016–2018. The maximum and minimum BC dry deposition was reported in pre- and post-monsoon respectively. Approximately 50% of annual dry deposition occurred in the pre-monsoon season (March to May) and 27% of the annual dry deposition occurred in April. The total dry BC deposition rate was estimated as ∼4.6 μg m−2 day−1 providing a total deposition of 531 μg m−2 during the pre-monsoon season. The contribution of biomass burning and fossil fuel sources to BC deposition on an annual basis was 28% and 72% respectively. The annual accumulated wet deposition of BC was 196 times higher than the annual dry deposition. The ten months of observed dry deposition of BC (October 1, 2016 to August 31, 2017 – except December 2016) was ∼39% lower than that of WRF-Chem's estimated annual dry deposition from September 1, 2016 to August 31, 2017 partially due to model bias. The deposited content of BC over the snow surface has an important role in albedo reduction, therefore snow samples were collected from the surface of the Yala Glacier and the surrounding region in April 2016, 2017, and 2018. Samples were analyzed for BC mass concentration through the thermal optical analysis and single particle soot photometer method. The BC calculated via the thermal optical method was in the range of 352–854 ng g−1, higher than the BC calculated through the particle soot photometer method and estimated BC in 2 cm surface snow (imperial equation). The maximum surface snow albedo reduction due to BC was 8.8%, estimated by a widely used snow radiative transfer model and a linear regression equation.

Modeling of mercury deposition in India: evaluating emission inventories and anthropogenic impacts.

Mercury (Hg), a ubiquitous atmospheric trace metal posing serious health risks, originates from natural and anthropogenic sources. India, the world's second-largest Hg emitter and a signatory to the Minamata Convention, is committed to reducing these emissions. However, critical gaps exist in our understanding of the spatial and temporal distribution of Hg across the vast Indian subcontinent due to limited observational data. This study addresses this gap by employing the GEOS-Chem model with various emission inventories (UNEP2010, WHET, EDGAR, STREETS, and UNEP2015) to simulate Hg variability across the Asian domain, with a specific focus on India from 2013 to 2017. Model performance was evaluated using ground-based GMOS observations and available literature data. Emission inventory performance varied across different observational stations. Hence, we employed ensemble results from all inventories. The maximum relative bias for Total Gaseous Mercury (TGM) and Gaseous Elemental Mercury (GEM; Hg0) concentrations is about ±20%, indicating simulations with sufficient accuracy. Total Hg wet deposition fluxes are highest over the Western Ghats and the Himalayan foothills due to higher rainfall. During the monsoon, the Hg wet deposition flux is about 65.4% of the annual wet deposition flux. Moreover, westerly winds cause higher wet deposition in summer over Northern and Eastern India. Total Hg dry deposition flux accounts for 72-74% of total deposition over India. Hg0 dry deposition fluxes are higher over Eastern India, which correlates strongly with the leaf area index. Excluding Indian anthropogenic emissions from the model simulations resulted in a substantial decrease (21.9% and 33.5%) in wet and total Hg deposition fluxes, highlighting the dominant role of human activities in Hg pollution in India.

Comparisons of Spatial and Temporal Variations in PM2.5-Bound Trace Elements in Urban and Rural Areas of South Korea, and Associated Potential Health Risks

PM2.5-bound trace elements were chosen for health risk assessment because they have been linked to an increased risk of respiratory and cardiovascular illness. Since the Korean national air quality standard for ambient particulate matter is based on PM2.5 mass concentration, there have only been a few measurements of PM2.5 particles together with trace elements that can be utilized to evaluate their effects on air quality and human health. Thus, this study describes the trace elements bound to PM2.5 in Seoul (urban area) and Seosan (rural area) using online nondestructive energy-dispersive X-ray fluorescence analysis from December 2020 to January 2021. At both the Seoul and Seosan sites, S, K, Si, Ca, and Fe constituted most of the PM2.5-bound trace elements (~95%); major components such as S, K, and soil (estimatedcalculatedcalculated based on oxides of Si, Fe, Ca, and Ti) were presumably from anthropogenic and crustal sources, as well as favorable meteorological conditions. During winter, synoptic meteorology favored the transport of particles from severely contaminated regions, such as the East Asian outflow and local emissions. The total dry deposition flux for crustal elements was 894.5 ± 320.8 µg m−2 d−1 in Seoul and 1088.8 ± 302.4 µg m−2 d−1 in Seosan. Moreover, potential health risks from the trace elements were estimated. Cancer risk values for carcinogenic trace elements (Cr, As, Ni, and Pb) were within the tolerable limit (1 × 10−6), suggesting that adults and children were not at risk of cancer throughout the study period in Seoul and Seosan. Furthermore, a potential risk assessment of human exposure to remaining carcinogens (Cr, As, Ni, and Pb) and non-carcinogens (Cu, Fe, Zn, V, Mn, and Se) indicated that these trace elements posed no health risks. Nevertheless, trace element monitoring, risk assessment, and mitigation must be strengthened throughout the study area to confirm that trace-element-related health effects remain harmless. Researchers and policymakers can use the database from this study on spatial and temporal variation to establish actions and plans in the future.

Contribution of biomass burning to black carbon deposition on Andean glaciers: consequences for radiative forcing

Andean glaciers have melted rapidly since the 1960s. While some melting is likely due to anthropogenic climate change driven by increasing greenhouse gases, deposition of light-absorbing particles such as black carbon (BC) may also play a role. We hypothesize that BC from fires in the Amazon Basin and elsewhere may be deposited on Andean glaciers, reducing the surface albedo and inducing further melting. Here we investigate the role of BC deposition on albedo changes in the Andes for 2014–2019 by combining atmospheric chemistry modeling with observations of BC in snow or ice at four mountain sites in Peru (Quelccaya, Huascarán, Yanapaccha, and Shallap) and at one site in Bolivia (Illimani). We find that annual mean ice BC concentrations simulated by the chemical transport model GEOS-Chem for 2014–2019 are roughly consistent with those observed at the site with the longest record, Huascarán, with overestimates of 15%–40%. Smoke from fires account for 20%–70% of total wet and dry deposition fluxes, depending on the site. The rest of BC deposited comes from fossil fuel combustion. Using a snow albedo model, we find that the annual mean radiative forcing from the deposition of smoke BC alone on snow ranges from +0.1 to +3.2 W m−2 under clear-sky conditions, with corresponding average albedo reductions of 0.04%–1.1%. These ranges are dependent on site and snow grain size. This result implies a potentially significant climate impact of biomass burning in the Amazon on radiative forcing in the Andes.

Comparison of vertical and horizontal atmospheric deposition of nitrate at Central European mountain-top sites during three consecutive winters

Nitrogen (N) deposition, a key process of atmospheric self-cleaning, represents an important pathway for nutrients and pollutants to ecosystems. Enhanced N deposition flux contributes to acidification, eutrophication and loss of biodiversity. N-NO3− concentrations in rime and snow were measured at 10 Czech plots situated in borderline mountains in 2009–2011 winters. The results were put in context with data-driven geostatistical modelling results of annual wet vertical and horizontal deposition. Our hypotheses were that: (i) rime and snow would be more polluted in the highly industrialized north than in the south, (ii) the N-NO3− concentrations would differ in the three winters studied, and (iii), that N-NO3− rime deposition is not negligible in Central European mountain ranges. Our results indicated that winter N-NO3− concentrations were significantly higher in rime than in snow and that there were much larger between-site differences in N-NO3− concentrations for rime than for snow. Relatively large differences were found between individual years. Atmospheric input of N-NO3− in winter was dominated by vertical deposition, i.e., snow. Modelled results showed that mean winter rime deposition corresponded to about 6–25 %, and mean winter snow deposition made up 25–72.5 % of mean annual N-NO3− wet-only deposition. Model N-NO3−occult deposition estimated from throughfall and total (wet and dry) deposition is highly uncertain, however: N throughfall is not a relevant proxy for estimation of realistic total N deposition due to N exchange between the tree canopy and atmosphere.

High NH3 deposition in the environs of a commercial fattening pig farm in central south China

Intensive livestock production has been increasing, and has resulted in the emission of more than seven teragram per year of ammonia (NH3) in China in recent years. However, little is known about the fate of the emitted NH3, especially the dry deposition of NH3 in the environs of intensive animal farms. In this study, the spatial and temporal variations of NH3 deposition in the environs of an intensive fattening pig farm were investigated in the central south of China. NH3 concentrations were measured at sites situated 50, 100, 200, 300, and 500 m in the downwind direction from the farm each month from July 2018 to June 2019. The NH3 deposition was calculated based on a bidirectional NH3 exchange model. The monthly NH3 emissions from the pig farm were estimated based on the breeding stock. The annual average NH3 concentrations ranged from 1200 to 14 μg m−3 at the downwind sites within 500 m of the pig farm, exhibiting exponential decay as distance increased. Strong seasonality in NH3 deposition was observed, with the highest season being in the summer and lowest in the winter, and air temperature was found to be an important factor affecting this seasonal variation. The estimated monthly total dry deposition within 500 m of the pig farm ranged from 92 to 1400 kg NH3–N mo−1, which accounted for 4.1%–14% of the total monthly NH3 emissions from the pig farm. The estimated total NH3 emissions and NH3 deposition from the pig farm were 63 000 kg NH3–N yr−1 and 5400 kg NH3–N yr−1, respectively, with the annual average ratio of NH3 deposition to NH3 emission being 8.6%. This study found NH3 deposition around intensive pig farms is high, and determined it as a significant fate of the NH3 emitted from pig farms.

Technical note: AQMEII4 Activity 1: evaluation of wet and dry deposition schemes as an integral part of regional-scale air quality models

We present in this technical note the research protocol for phase 4 of the Air Quality Model Evaluation International Initiative (AQMEII4). This research initiative is divided into two activities, collectively having three goals: (i) to define the current state of the science with respect to representations of wet and especially dry deposition in regional models, (ii) to quantify the extent to which different dry deposition parameterizations influence retrospective air pollutant concentration and flux predictions, and (iii) to identify, through the use of a common set of detailed diagnostics, sensitivity simulations, model evaluation, and reduction of input uncertainty, the specific causes for the current range of these predictions. Activity 1 is dedicated to the diagnostic evaluation of wet and dry deposition processes in regional air quality models (described in this paper), and Activity 2 to the evaluation of dry deposition point models against ozone flux measurements at multiple towers with multiyear observations (to be described in future submissions as part of the special issue on AQMEII4). The scope of this paper is to present the scientific protocols for Activity 1, as well as to summarize the technical information associated with the different dry deposition approaches used by the participating research groups of AQMEII4. In addition to describing all common aspects and data used for this multi-model evaluation activity, most importantly, we present the strategy devised to allow a common process-level comparison of dry deposition obtained from models using sometimes very different dry deposition schemes. The strategy is based on adding detailed diagnostics to the algorithms used in the dry deposition modules of existing regional air quality models, in particular archiving diagnostics specific to land use–land cover (LULC) and creating standardized LULC categories to facilitate cross-comparison of LULC-specific dry deposition parameters and processes, as well as archiving effective conductance and effective flux as means for comparing the relative influence of different pathways towards the net or total dry deposition. This new approach, along with an analysis of precipitation and wet deposition fields, will provide an unprecedented process-oriented comparison of deposition in regional air quality models. Examples of how specific dry deposition schemes used in participating models have been reduced to the common set of comparable diagnostics defined for AQMEII4 are also presented.

Numerical simulation of the 18 February 2017 frontal dust storm over southwest of Iran using WRF-Chem, satellite imagery, and PM10 concentrations

In the past two decades, dust storms in the Middle East have caused many problems for people in the south and southwest regions of Iran. During this period, there has been an increase in the trend of strong dust storm activities in this region, even in non-summer seasons. In this research, the February 18, 2017 frontal dust storm over the Khuzestan province of Iran is studied in detail. Satellite images, synoptic data, PM10 data, aerosol index, and numerical simulation were used to analyze the event. The simulation results indicated that about 1.2 Tg of dust was emitted from the simulation area between 17–18 February 2017. About 0.2 Tg of the emitted dust was deposited in the simulation area during 17–18 February. Comparing the emission and deposition amounts showed that although the Khuzestan province had a contribution of about 1% to the total dust emission, it hosted about 16% of the total dry deposition. These results show that the main sources of dust in the Khuzestan province are external and it requires international cooperation and management.

Ammonia Dry Deposition in an Alpine Ecosystem Traced to Agricultural Emission Hotpots.

Elevated reactive nitrogen (Nr) deposition is a concern for alpine ecosystems, and dry NH3 deposition is a key contributor. Understanding how emission hotspots impact downwind ecosystems through dry NH3 deposition provides opportunities for effective mitigation. However, direct NH3 flux measurements with sufficient temporal resolution to quantify such events are rare. Here, we measured NH3 fluxes at Rocky Mountain National Park (RMNP) during two summers and analyzed transport events from upwind agricultural and urban sources in northeastern Colorado. We deployed open-path NH3 sensors on a mobile laboratory and an eddy covariance tower to measure NH3 concentrations and fluxes. Our spatial sampling illustrated an upslope event that transported NH3 emissions from the hotspot to RMNP. Observed NH3 deposition was significantly higher when backtrajectories passed through only the agricultural region (7.9 ng m-2 s-1) versus only the urban area (1.0 ng m-2 s-1) and both urban and agricultural areas (2.7 ng m-2 s-1). Cumulative NH3 fluxes were calculated using observed, bidirectional modeled, and gap-filled fluxes. More than 40% of the total dry NH3 deposition occurred when air masses were traced back to agricultural source regions. More generally, we identified that 10 (25) more national parks in the U.S. are within 100 (200) km of an NH3 hotspot, and more observations are needed to quantify the impacts of these hotspots on dry NH3 deposition in these regions.

Concentrations and biosphere–atmosphere fluxes of inorganic trace gases and associated ionic aerosol counterparts over the Amazon rainforest

Abstract. The Amazon rainforest presents a unique, natural laboratory for the study of surface–atmosphere interactions. Its alternation between a near-pristine marine-influenced atmosphere during the wet season and a vulnerable system affected by periodic intrusions of anthropogenic pollution during the dry season provides an opportunity to investigate some fundamental aspects of boundary-layer chemical processes. This study presents the first simultaneous hourly measurements of concentrations, fluxes, and deposition velocities of the inorganic trace gases NH3, HCl, HONO, HNO3, and SO2 as well as their water-soluble aerosol counterparts NH4+, Cl−, NO2-, NO3- and SO42- over the Amazon. Species concentrations were measured in the dry season (from 6 October to 5 November 2017), at the Amazon Tall Tower Observatory (ATTO) in Brazil, using a two-point gradient wet-chemistry instrument (GRadient of AErosols and Gases Online Registration, GRAEGOR) sampling at 42 and 60 m. Fluxes and deposition velocities were derived from the concentration gradients using a modified form of the aerodynamic gradient method corrected for measurement within the roughness sub-layer. Findings from this campaign include observations of elevated concentrations of NH3 and SO2 partially driven by long-range transport (LRT) episodes of pollution and the substantial influence of coarse Cl− and NO3- particulate on overall aerosol mass burdens. From the flux measurements, the dry season budget of total reactive nitrogen dry deposition at the ATTO site was estimated as −2.9 kg N ha-1a-1. HNO3 and HCl were deposited continuously at a rate close to the aerodynamic limit. SO2 was deposited with an average daytime surface resistance (Rc) of 28 s m−1, whilst aerosol components showed average surface deposition velocities of 2.8 and 2.7 mm s−1 for SO42- and NH4+, respectively. Deposition rates of NO3- and Cl− were higher at 7.1 and 7.8 mm s−1, respectively, reflecting their larger average size. The exchange of NH3 and HONO was bidirectional, with NH3 showing emission episodes in the afternoon and HONO in the early morning hours. This work provides a unique dataset to test and improve dry deposition schemes for these compounds for tropical rainforest, which have typically been developed by interpolation from conditions in temperate environments. A future campaign should focus on making similar measurements in the wet season in order to provide a complete view of the annual pattern of inorganic trace gas and coarse aerosol biosphere–atmosphere exchange over tropical rainforest.

A study of atmospheric pollutants (particulates, metallic elements) at an agricultural site

In this study, the total suspended particulate (TSP) concentrations and dry deposition of ambient air particulates are measured using a high-volume air sampler and a dry deposition plate at an agricultural sampling site in central Taiwan from March of 2019 to February of 2020. In addition, the concentrations of metallic elements attached to the particulates and dry deposits are analyzed using inductively coupled plasma atomic emission spectroscopy (ICP-AES). Finally, the TSP and metallic elements concentrations in TSP at different sampling sites around the world are also compared and discussed. The results indicated that the average highest TSP concentrations and dry depositions values both occurred in autumn, and the agricultural sampling site had the average greatest ambient air particulates dry depositions velocities when compared with other previous characteristic-related studies in Taiwan. In addition, metallic element Al had the average highest concentrations and dry depositions and metallic element Cd had the average lowest concentrations and dry depositions values in this study. In addition, metallic elements Cr, Cu, Pb, and Zn had the average highest concentrations when compared with other typical sampling site studies (airport, suburban, downtown, residential, industrial, and wetlands) in central Taiwan. Furthermore, when compared with the other previous metallic elements concentrations found in related studies in other regions from 1978 to 2020, the results obtained in this study indicated that the average metallic element concentrations Cr, Cu, Pb, and Zn in Taiwan were only lower than those reported in India and China. Taiping District is the main fruits production area in central Taiwan. Therefore, continued monitoring of ambient air related pollutants and finding the possible pollution sources have become an important issue for this agricultural site. From the above analysis, we also conclude that ambient air particulates and all the metallic elements dry deposition values obtained in this study were higher than those from the other characteristic sampling sites where studies were previously conducted in Taiwan.

Origin, transport and deposition of aerosol iron to Australian coastal waters

Australia is a major source of Fe-laden dust to the anemic marine phytoplankton in the Southern Ocean and to Southern Hemisphere (SH) low latitudes diazotrophic bacteria. However, the paucity of observations and laboratory experiments on SH aerosols biases model predictions of atmospheric Fe deposition to the southern oceans and the subsequent response of ocean productivity. As a result of an extensive shipboard aerosol sampling effort, this study presents laboratory measurements of aerosol Fe concentrations, solubilities and fluxes and analysis of chemical tracers, highlighting the large heterogeneity between aerosol Fe sources in 5 coastal regions around Australia. While dust-sourced high Fe loadings and low Fe solubilities (5%) aerosols dominate the atmospheric burden of the western coasts of Australia, much lower Fe concentrations but greater Fe solubilities (10.5% and 13%) were measured in aerosols along the east coast which was attributed to solubility-enhancing atmospheric reactions with anthropogenic pollutants. Surprisingly high aerosol Fe solubilities (>20%) in northern Australia aerosols were associated with direct emissions or atmospheric reactions with bushfire emissions at tropical latitudes, which accounted for 49% of the total (sum) atmospheric dry deposition flux of labile Fe measured across the continent's surrounding seawaters in this study.

Wet deposition of sulfur and nitrogen at Mt. Emei in the West China Rain Zone, southwestern China: Status, inter-annual changes, and sources

The West China Rain Zone (WCRZ) is of ecological importance and thus, anthropogenic impacts on its vitality are of concern. To ascertain if China's SO2 and NOx emissions reductions in the recent years are reflected in reduced impacts, sulfur and nitrogen wet deposition at Mt. Emei was observed during 2017–2019. The source contributions to sulfur and nitrogen wet deposition were estimated using the positive matrix factorization (PMF) and the source-oriented Community Multi-scale Air Quality (CMAQ) model. The annual Volume Weighted Mean (VWM) pH of precipitation increased from 4.01 to 4.75 in the 1980s–2000s to 5.39 in 2017–2019. However, 12% of the samples during 2017–2019 had pH < 4.50. The VWM SO42− concentration decreased from 80.9 to 26.0 μeq L−1 from 2007–2009 to 2017–2019. The VWM NO3− concentration (18.3 μeq L−1) in 2017–2019 was close to that measured in 2007–2009. Although the dry deposition fluxes onto forest canopy were under-estimated, the mean annual total wet and dry deposition flux of nitrogen (24.3 kg N ha−1 yr−1) was higher than the critical load (CL: 10.0–15.0 kg N ha−1 yr−1), while the flux of sulfur (12.1 kg S ha−1 yr−1) was lower than the CL (16.0–32.0 kg S ha−1 yr−1). The annual wet deposition fluxes of SO42− and NO3− were mainly from industries (54% and 43%, respectively) and power plants (21% and 25%, respectively), and that of NH4+ was mostly from agriculture (88%). Emissions within and outside the Sichuan Basin (SCB) were both important sources of the wet deposition fluxes of sulfur (45% and 39%, respectively) and nitrogen (68% and 29%, respectively), and other unidentified sources accounted for 16% and 3% of the sulfur and nitrogen fluxes, respectively. This study suggests that to protect Mt. Emei's ecosystems, efforts are needed to further control sulfur and nitrogen deposition through reducing emissions within and outside the SCB.

Update and evaluation of the ozone dry deposition in Oslo CTM3 v1.0

Abstract. High concentrations of ozone in ambient air are hazardous not only to humans but to the ecosystem in general. The impact of ozone damage on vegetation and agricultural plants in combination with advancing climate change may affect food security in the future. While the future scenarios in themselves are uncertain, there are limiting factors constraining the accuracy of surface ozone modeling also at present: the distribution and amount of ozone precursors and ozone-depleting substances, the stratosphere–troposphere exchange, as well as scavenging processes. Removal of any substance through gravitational settling or by uptake by plants and soil is referred to as dry deposition. The process of dry deposition is important for predicting surface ozone concentrations and understanding the observed amount and increase of tropospheric background ozone. The conceptual dry deposition velocities are calculated following a resistance-analogous approach, wherein aerodynamic, quasi-laminar, and canopy resistance are key components, but these are hard to measure explicitly. We present an update of the dry deposition scheme implemented in Oslo CTM3. We change from a purely empirical dry deposition parameterization to a more process-based one which takes the state of the atmosphere and vegetation into account. We examine the sensitivity of the scheme to various parameters, e.g., the stomatal conductance-based description of the canopy resistance and the choice of ozone surface resistance, and evaluate the resulting modeled ozone dry deposition with respect to observations and multi-model studies. Individual dry deposition velocities are now available for each land surface type and agree generally well with observations. We also estimate the impact on the modeled ozone concentrations at the surface. We show that the global annual total ozone dry deposition decreases with respect to the previous model version (−37 %), leading to an increase in surface ozone of more than 100 % in some regions. While high sensitivity to changes in dry deposition to vegetation is found in the tropics and the Northern Hemisphere, the largest impact on global scales is associated with the choice of prescribed ozone surface resistance over the ocean and deserts.

Eight-year dry deposition of atmospheric mercury to a tropical high mountain background site downwind of the East Asian continent

Atmospheric deposition, either dry or wet, has been identified as an important pathway of mercury (Hg) input to terrestrial and aquatic systems. Although East Asia is the major atmospheric Hg emission source region, very few studies have been conducted to quantify atmospheric Hg deposition in its downwind region. In this study, 8-year (2009–2016) atmospheric Hg dry deposition was reported at the Lulin Atmospheric Background Station (LABS), a high mountain forest site in central Taiwan. Dry deposition of speciated Hg was estimated using a bi-directional air-surface flux exchange model for gaseous elemental mercury (GEM) and dry deposition models for gaseous oxidized mercury (GOM) and particulate-bound mercury (PBM), making use of the monitored speciated atmospheric Hg concentrations. Annual total Hg dry deposition ranged from 51.9 to 84.9 μg m−2 yr−1, with a multi-year average of 66.1 μg m−2 yr−1. Among the three forms of atmospheric Hg, GEM was the main contributor to the total dry deposition, contributing about 77.8% to the total, due to the high density of forest canopy as well as the much higher concentration of GEM than GOM and PBM at LABS. Mercury dry deposition is higher in winter and spring than in summer and fall, partly due to the elevated Hg concentrations associated with air masses from East and Southeast Asia where with high atmospheric Hg emissions. The mean annual dry/wet deposition ratio of 2.8 at LABS indicated that Hg deposition to forest landscape was governed by dry rather than wet deposition.

An Overview of Atmospheric Reactive Nitrogen Research: South Asian Perspective

The unprecedented increase in Nr is causing several environmental problems such as eutrophication, ozone depletion and climate change etc. Excessive Nr creation is also responsible for poor plant and human health, soil acidification, groundwater contamination etc. Inhabiting ~ one-fourth population of the world and sharing only 4.9% of land of the total global landmass, the South Asian region consumes 60% of the total global fertilizer nutrient. India is the largest consumer of synthetically produced fertilizer in South Asia. According to estimates, India consumes ~ 17 million tonnes Nr/yr, making South Asia and India a hot spot for the deposition of N species. In India, the fertilizer N consumption is increased 314 folds from 1950-51 to 2013-14. In 1951-52 per hectare fertilizer N consumption was 0.44 kgha-1 while it was 86.2 kgha-1 in 2013-14. Since rains are limited to a few months, most of the time the weather is hot and dry. And hence, the dry deposition is the key mechanism of pollutant removal in the region. Wet deposition predominantly occurs during the monsoon period. The wet deposition of NH3-N observed to be the highest in the Indo-Gangetic plains. The annual NO3-N deposition at the urban, suburban, rural and industrial site found to be 4.48, 2.10, 4.06 and 3.92 kgha-1 respectively, and the annual deposition of NH4-N at the urban, suburban, rural and industrial site found to be 2.38, 2.10, 2.38 and 5.05 kgha-1 respectively. The average total wet deposition of NO3-N and NH4-N in India is estimated to be 6.01kgha-1 which is equivalent to 1.97 Tg N/yr. The average total dry deposition of NH4-N and NO3-N through dust fall found to be 0.37 kg ha-1 and 0.84 kg ha-1 respectively. The average total dry deposition of NH4-N and NO3-N in the form of aerosols found to be 0.28 and 1.65 kg ha-1 while through gaseous dry deposition it was 4.72 kg ha-1 and 0.28 kg ha-1 for NH4-N and NO3-N respectively. This study highlights the need for integrated nitrogen monitoring and assessment in South Asia.

Measurement of size-fractionated particulate-bound mercury in Beijing and implications on sources and dry deposition of mercury

Particulate-bound mercury (PBM) plays an important role in the Hg cycling and is with high concentration in urban area. Totally 10-staged (range of 0.01–10μm) size-fractionated PBM was measured in Beijing during December 2016–November 2017. Our study indicated that Beijing suffered from heavy PBM pollution, with an annual average of 297.9 (17.2–1906.6) pgm−3, 22.2–52.5 times higher than that observed in North America. Overall, the concentration of PBM2.5 (PBM2.5 and PBM2.5–10 meant PBM concentration in PM with aerodynamic diameter <2.5μm and in the range of 2.5–10μm, respectively) accounted for 75%–87% of PBM10 in all seasons. The increase of PBM2.5–10 in the polluted days (PM2.5>75μgm−3) indicated the primary influence from natural sources while anthropogenic sources and secondary conversion caused the growth of PBM2.5 concentration. In addition, the generation of secondary PBM during the transport process contributed to the generation of PBM in Beijing, especially when the PM concentrations increase simultaneously. The local emissions and physicochemical conversion were the dominant cause of extremely high PBM pollution event in winter. Enhanced PBM concentrations also lead to severe dry deposition of PBM in Beijing. The estimated annual dry deposition of PBM was 40.6μgm−2yr−1, which was 3.1–203.0 times than observations from other sites in northern hemisphere. PBM2.5 contributed 53% of total dry deposition in all seasons, significantly higher than the other observation sites (28%–36%). In addition, the proportion of PBM2.5 deposition in PBM10 deposition ranged from 47% in summer to 66% in winter, which indicated that both seasonal variations of PBM size distribution characteristics should be taken into consideration. Results from this study revealed the size distribution and dry deposition characteristics of PBM in urban Beijing and provided base for the implementation of Minamata convention on mercury.

Nitrogen dry deposition to Lake Superior and Lake Michigan

Abstract Nitrate (NO3−) levels in Lake Superior have increased from historic levels of about 5 μM to its current concentration of about 25 μM. The atmosphere makes a substantial contribution to the nitrogen budgets for Lake Superior and Lake Michigan. This study provides a more well-defined estimate of nitrogen dry deposition rates derived from the measurement of over-water concentrations, and in situ meteorological measurements, which were input into the Resistance Model. We obtained a nitrogen dry deposition rate of [(3.41 ± 2.26) × 107 kg N/yr; (5.90 ± 3.91) kg N/ha/yr] over Lake Michigan, and [(1.54 ± 1.06) × 107 kg N/yr; (1.87 ± 1.27) kg N/ha/yr] over Lake Superior. Nitric acid (HNO3), which originates from the combustion of fossil fuels, contributes 84% of the total nitrogen dry deposition to Lake Michigan; and 66% to Lake Superior. Ammonia (NH3), which originates from agricultural activities and gasoline combustion, is the second highest contributor of nitrogen dry deposition to both lakes: contributing 13% to Lake Michigan and 32% to Lake Superior. The nitrogen dry deposition is approximately 68% of the nitrogen wet deposition over Lake Superior, and approximately 80% of wet deposition over Lake Michigan. The over-water dry deposition velocity of HNO3 and NH3 were also evaluated. We obtained morning deposition velocities of 0.099 cm/s for NH3 and 0.095 cm/s for HNO3; and afternoon values of 0.137 cm/s for NH3 and 0.132 cm/s for HNO3. Another key finding is that the atmospheric concentrations of nitrogen compounds near Lake Michigan and Lake Superior have decreased since 2003.

Deposition Mapping of Polycyclic Aromatic Compounds in the Oil Sands Region of Alberta, Canada and Linkages to Ecosystem Impacts.

This study produced gridded deposition estimates of polycyclic aromatic compounds (PACs), including 17 polycyclic aromatic hydrocarbons (PAHs), 21 alkylated PAHs (alk-PAHs), and 5 dibenzothiophenes (DBTs), over the oil sands region of Alberta, Canada and surrounding communities. Gridded annual total deposition of PACs in 2011 ranged from 55 to 175 000 μg m-2 yr-1 and the mean and median fluxes were 1700 and 760 μg m-2 yr-1, respectively. The domain-wide mean dry and wet deposition were 600 and 1100 μg m-2 yr-1. PAHs, alk-PAHs and DBTs contributed 19%, 74%, and 7% to the total dry deposition, and 42%, 49%, and 9% to the total wet deposition. Dominant chemical species contributing to total deposition were naphthalene, retene and phenanthrene for PAHs and C2-benz[a]anthracene/triphenylene/chrysene, C2-fluoranthene/pyrene and C2-fluorene for alk-PAHs. The highest PAC deposition was found over the surface mineable area, which received 9 times the deposition flux of outlying areas. Additional deposition hotspots were also observed south of the surface mineable area notably over in situ bitumen production sites. The deposition of alk-PAHs impacted a more extensive area than that of PAHs or DBTs. This result suggests that atmospheric deposition is a key process in wildlife exposure to PACs across the region.

Characteristics of Nitrogen Deposition in Heilongjiang Liangshui National Nature Reserve

To investigate the nitrogen deposition status in Heilongjiang Liangshui National Nature Reserve, a G78 nitrogen deposition collector was used to monitor dry particulate nitrogen deposition and wet nitrogen deposition during the growing season in 2015, and a bucket was used to monitor bulk nitrogen deposition during non-growing season. The results showed that:①Total nitrogen deposition (wet nitrogen deposition+dry particulate nitrogen deposition during the growing season and bulk deposition during the non-growing season) was 12.93 kg·(hm2·a)-1, inorganic nitrogen deposition was 8.27 kg·(hm2·a)-1 with NH4+/NO3- ratio of 1.3; organic nitrogen deposition was 4.66 kg·(hm2·a)-1, which was equivalent to 36.0% of the total nitrogen deposition. ②Total nitrogen deposition in the growing season (wet+dry particulate deposition) and non-growing season (bulk deposition) were 11.42 kg·hm-2 and 1.51 kg·hm-2respectively, which account for 88.3% and 11.7% of the total nitrogen deposition respectively. ③Total wet nitrogen deposition during the growing season was 9.28 kg·hm-2, contributing to 81.3% of the total nitrogen deposition in the growing season, and was positively correlated with precipitation (R2=0.87, P<0.001); total dry particulate nitrogen deposition in the growing season was 2.14 kg·hm-2, which was 18.7% of the total nitrogen deposition in growing season. Wet nitrogen deposition in this region is moderate compared with other regions in China, and is significantly affected by precipitation. There is a potential risk of environmental pollution in this region. Thus, environmental protection and water quality monitoring are required in the process of production.