Wet Sulfur Research Articles

Projected global sulfur deposition with climate intervention

Even with immediate implementation of global policies to mitigate carbon dioxide emissions, the impacts of climate change will continue to worsen over the next decades. One potential response is stratospheric aerosol injection (SAI), where sulfur dioxide is released into the stratosphere to block incoming solar radiation. SAI does not reduce the level of carbon dioxide in the atmosphere, but it can slow warming and act as a stopgap measure to give the world more time to pursue effective carbon reduction strategies. While SAI is controversial, it remains a technically feasible proposition. It ought to be thoroughly modeled both to characterize global risks better and to further the scientific community’s understanding of stratospheric aerosol dynamics. SAI relies on sulfate aerosols which have a lifetime of several years in the stratosphere but will eventually be deposited back onto Earth’s surface. While sulfate is an important nutrient for many ecosystems, high concentrations can cause acidification, eutrophication, and biodiversity loss. We use model outputs from the Geoengineering Model Intercomparison Project (GeoMIP) to track the impacts of sulfur deposition from SAI to various ecoregions through comparison with historical climate and future Shared Socioeconomic Pathway (SSP) scenarios. Our results demonstrate that dry sulfur deposition will continue to decline worldwide, regardless of scenario, from a high of 41 Tg S/yr in 1981 to under 20 Tg S/yr by 2100. Wet sulfur deposition, however, is much more uncertain and further work needs to be done in this area to harmonize model estimates. Under SAI, many ecoregions will experience notably different sulfur deposition regimes by the end of the century compared to historical trends. In some places, this will not be substantially different than the impacts of climate change under SSP2–4.5 or SSP5–8.5. However, in some ecoregions the model projections disagree dramatically on the magnitude of future trends in both emissions and deposition, with, for example, UKESM1–0-LL projecting that SO42- deposition in deciduous needleleaf forests under G6 Sulfur will reach 394 % of SSP2–4.5 deposition by the 2080 s while CESM2-WACCM projects that SO42- deposition will remain at 170 % of SSP2–4.5 deposition during that same time period. Our work emphasizes the lack of agreement between models and the importance of improving our understanding of SAI impacts for future climate decision-making.

How do different marine engine fuels and wet scrubbing affect gaseous air pollutants and ozone formation potential from ship emissions?

Sulphur Emission Control Areas (SECAs), mandated by the International Maritime Organization (IMO), regulate fuel sulphur content (FSC) to mitigate the environmental and health impact of shipping emissions in coastal areas. Currently, FSC is limited to 0.1% (w/w) within and 0.5% (w/w) outside SECAs, with exceptions for ships employing wet sulphur scrubbers. These scrubbers enable vessels using non-compliant fuels such as high-sulphur heavy fuel oils (HFOs) to enter SECAs. However, while sulphur reduction via scrubbers is effective, their efficiency in capturing other potentially harmful gases remains uncertain. Moreover, emerging compliant fuels like highly aromatic fuels or low-sulphur blends lack characterisation and may pose risks.Over three years, we assessed emissions from an experimental marine engine at 25% and 75% load, representative of manoeuvring and cruising, respectively. First, characterizing emissions from five different compliant and non-compliant fuels (marine gas oil MGO, hydro-treated vegetable oil HVO, high-, low- and ultra-low sulphur HFOs), we calculated emission factors (EF). Then, the wet scrubber gas-phase capture efficiency was measured using compliant and non-compliant HFOs.NOx EF varied among fuels (5200–19700 mg/kWh), with limited scrubber reduction. CO (EF 750–13700 mg/kWh) and hydrocarbons (HC; EF 122–1851 mg/kWh) showed also insufficient abatement. Carcinogenic benzene was notably higher at 25% load and about an order of magnitude higher with HFOs compared to MGO and HVO, with no observed scrubber reduction. In contrast, carbonyls such as carcinogenic formaldehyde and acetaldehyde, acting as ozone precursors, were effectively scrubbed due to their polarity and water solubility. The ozone formation potential (OFP) of all fuels was examined.Significant EF differences between fuels and engine loads were observed, with the wet scrubber providing limited or no reduction of gaseous emissions. We suggest enhanced regulations and emission abatements in the marine sector to mitigate gaseous pollutants harmful to human health and the environment.

Bioleaching of a lateritic ore (Piauí, Brazil) in percolators

Heap leaching of laterites for extraction of nickel and cobalt is an attractive alternative to capital and energy intensive high pressure acid leaching, the dominant hydrometallurgical processing technology for limonitic laterites. Conventional approach for heap leaching of laterites is leaching with sulfuric acid. Consumption of sulfuric acid during heap leaching is substantial and industrial-scale operations require construction of a sulfuric acid production plant on site. In this study, heap bioleaching of laterites was simulated in laboratory scale column percolators and bioleaching of nickel and cobalt from lateritic material was successfully demonstrated for the first time. The process is based on biooxidation of the bacterially modified “wet sulfur” inside column percolators by sulfur-oxidizing acidophilic bacteria Acidithiobacillus thiooxidans. The “wet sulfur“ was generated in a bioreactor with the bacterial culture, harvested, and mixed with lateritic ore before forming agglomerates to be filled in the percolator columns. Liquid was circulated with a flow rate of 8 mL/min. Maximum metal extraction was 66% nickel, 95% cobalt, 10% iron, 55% magnesium and 89% manganese from the Piauí lateritic ore after one month bioleaching. For comparison, chemical leaching with 1 M sulfuric acid with or without addition of 10 g/L of ferrous sulfate heptahydrate as reductant resulted in extraction of approximately 80% nickel, 86% cobalt, 33% iron, 50% magnesium and 81% manganese. With bioleaching a higher cobalt but lower nickel and iron extraction was achieved, i.e. a better selectivity of nickel over iron extraction, as well as a relatively higher pH of the pregnant leach solution requiring less limestone and, consequently, lower CO2 emission and generation of iron cake waste in case of laterite bioleaching. Overall, the results are promising and show potential of laterite heap bioleaching to be further developed to application on industrial scale.

Wet deposition of sulfur and nitrogen in the Jiuzhaigou World Heritage Site, China: Spatial variations, 2010–2022 trends, and implications for karst ecosystem conservation

Excessive sulfur and nitrogen deposition is a threat to natural ecosystems. This study investigated the spatio-temporal changes of wet sulfur and nitrogen deposition in Jiuzhaigou to understand the responses of wet deposition chemistry to local and national air pollutant emission changes and to assess relevant ecological risks. The results show that local emission sources (e.g., tourism, post-earthquake reconstruction, and vegetation damages) largely elevated the concentrations of SO42−, NO3−, NH4+, and Ca2+ at the non-background sites during 2021–2022; However, the gaps of annual sulfur and nitrogen wet deposition fluxes among the background, semi-background, and non-background sites were reduced by annual precipitation. The pH was also higher at the non-background sites due to stronger acid neutralization capacities from crustal dust there, and acid precipitation (pH < 5.6) was not detected at all the sites. During the 2010 to 2022 period, the wet deposition of SO42− and TIN (i.e. total inorganic nitrogen) and the equivalent ratio of SO42−: NO3− generally presented a declining trend at the background and semi-background sites, as a result of regional and national emission reductions. The TIN reduction from 2015 to 2016 to 2021–2022 at the background site was more from wet NH4+ deposition and the site's NO3− concentrations and fluxes were relatively stable. Compared to the critical loads (CLs) of sulfur and nitrogen for acidification and eutrophication, the annual wet and wet+dry deposition fluxes of sulfur and nitrogen were lower in almost the entire watershed, except for the CLmin of nitrogen for acidification in considerable areas. However, all the wet deposition samples were calcite-unsaturated and had annual TIN concentrations higher than the national environmental standard of total nitrogen for surface water. More field investigations are needed to better assess the ecological risks.

Humic-like Substances (HULIS) in Ship Engine Emissions: Molecular Composition Effected by Fuel Type, Engine Mode, and Wet Scrubber Usage.

Humic-like substances (HULIS), known for their substantial impact on the atmosphere, are identified in marine diesel engine emissions obtained from five different fuels at two engine loads simulating real world scenarios as well as the application of wet sulfur scrubbers. The HULIS chemical composition is characterized by electrospray ionization (ESI) ultrahigh resolution mass spectrometry and shown to contain partially oxidized alkylated polycyclic aromatic compounds as well as partially oxidized aliphatic compounds, both including abundant nitrogen- and sulfur-containing species, and clearly different to HULIS emitted from biomass burning. Fuel properties such as sulfur content and aromaticity as well as the fuel combustion efficiency and engine mode are reflected in the observed HULIS composition. When the marine diesel engine is operated below the optimum engine settings, e.g., during maneuvering in harbors, HULIS-C emission factors are increased (262-893 mg kg-1), and a higher number of HULIS with a shift toward lower degree of oxidation and higher aromaticity is detected. Additionally, more aromatic and aliphatic CHOS compounds in HULIS were detected, especially for high-sulfur fuel combustion. The application of wet sulfur scrubbers decreased the HULIS-C emission factors by 4-49% but also led to the formation of new HULIS compounds. Overall, our results suggest the consideration of marine diesel engines as a relevant regional source of HULIS emissions.

An acid rain–friendly NH3 control strategy to maximize benefits toward human health and nitrogen deposition

Ammonia (NH3) abatement remains controversial in China owing to its effectiveness in reducing PM2.5 pollution and nitrogen deposition but with the potential risk of promoting acid rain formation, necessitating scientific guidance. Here, we propose a novel method for designing an NH3 control strategy to mitigate both air pollution and nitrogen deposition without significantly exacerbating acid rain. This method involves extending the response surface model (RSM) to deposition using a delicately developed polynomial response function of deposition (i.e., dep-RSM). The Yangtze River Delta (YRD) dep-RSM application reveals that 16 out of 41 cities have NH3 control potentials from 15 % to 71 %. Excellent NH3 control potentials have been noted between April and June (78 %–92 %). From 2013 to 2017, the effective SO2 and NOx control significantly reduced wet sulfur and oxidized nitrogen deposition, providing considerable NH3 abatement potentials (15 %–24 %) to further reduce PM2.5 and nitrogen deposition by up to 2 % and 9 %, respectively, without acid rain exacerbation (the wet neutralization factor was maintained). Additionally, 57 % and 73 % NH3 emission reduction potentials were obtained under acid rain constraints with 75 % and 86 % reductions in the other precursors to reduce the average PM2.5 concentration below 25 and 15 μg/m3, and an additional 8408 and 14,459 premature deaths could only be avoided at an extra cost of 8.7 and 19.7 billion CNY, respectively. Meanwhile, the N deposition considerably reduced by 10 and 13 kgN/ha·yr. However, the YRD region could still simultaneously obtain substantial amounts of PM2.5 and N deposition mitigation using the strategy proposed herein. The expanded optimization system can be directly adopted by policymakers to implement coordinated control in regions or countries facing the same NH3 control conundrum.

In-vitro Evaluation of Fungicides against Leaf Spot and Flower Blight of Marigold

Marigold belonging to family Asteraceae, are most common in plant kingdom. It is an important commercial ornamental plant and garden flower. It is found in different colours and different fragrance. Yellow colour is most common. Leaf spot and flower blight is serious disease of marigold causing yield loss in crop. The present investigation was carried out with an objective to study the efficacy of new fungicides available in the market in in-vitrocondition. Eleven fungicides such as azoxystrobin, tebuconazole, azoxystrobin + tebuconazole, difenoconazole, azoxystrobin + difenoconazole, tebuconazole + sulphur, wet sulphur, mancozeb, metalaxly, chlorothalonil, chlorothalonil + metalaxly were evaluated at the concentration of 0.1%, 0.15% ,0.1%, 0.1%, 0.1%, 0.15%, 0.25%, 0.3%,0.2%, 0.3%, and 0.3% respectively. it has been found that combination of azoxystrobin + tebuconazole recorded mycelia growth inhibition of (97.30%) followed by tebuconazole + sulphur (95.95%) and Metalaxly of 95.05%. The least inhibition of 18.47% was recorded by wettable sulphur. Further the effectiveness of new fungicides may be tested under field condition against Alternaria zinniae.

Climate and atmospheric deposition drive the inter-annual variability and long-term trend of dissolved organic carbon flux in the conterminous United States

The lateral flux of dissolved organic carbon (DOC) from soils to inland waters and ultimately to the ocean represents a fundamental component of the global carbon cycle. To estimate the DOC flux, we developed an empirical terrestrial-aquatic DOC fluxes model (TAF-DOC). TAF-DOC incorporates various environmental factors (e.g., meteorology, sulfur, and nitrogen deposition) that to-date have not been comprehensively considered or well-represented in existing modeling frameworks. TAF-DOC was applied to estimate spatial-temporal patterns of DOC flux and potential fates across the conterminous United States during the 1985 to 2018 time period. Our results suggest that TAF-DOC successfully characterized spatial-temporal of DOC flux. As expected, the interannual pattern of DOC flux was strongly regulated by precipitation, but the long-term trend was significantly influenced by the rate of atmospheric wet sulfur deposition. From 1985 to 2018, TAF-DOC estimated DOC loading from terrestrial to aquatic ecosystems in the conterminous United States to be 33.5 ± 2.2 TgC per year, which was roughly 0.39–0.49% of total soil organic carbon stock estimates. The dominant fate of terrestrially-derived DOC was delivery to the coastal ocean in riverine export (41%), with another 21% buried in sediment and the remaining 12.8 ± 0.4 TgC per year (38%) returned to the atmosphere through outgassing from inland waters. Assuming the quantities of DOC sediment burial and export to the ocean as an annual sink of terrestrially-derived carbon, budget inventories and models that do not account for DOC flux in the conterminous United States will underestimate the net annual carbon sink by as much as 5.5–6.4%.

Estimating monthly wet sulfur (S) deposition flux over China using an ensemble model of improved machine learning and geostatistical approach

The wet S deposition was treated as a key issue because it played the negative on the soil acidification, biodiversity loss, and global climate change. However, the limited ground-level monitoring sites make it difficult to fully clarify the spatiotemporal variations of wet S deposition over China. Therefore, an ensemble model of improved machine learning and geostatistical method named fruit fly optimization algorithm-random forest-spatiotemporal Kriging (FOA-RF-STK) model was developed to estimate the nationwide S deposition based on the emission inventory, meteorological factors, and other geographical covariates. The ensemble model can capture the relationship between predictors and S deposition flux with the better performance (R2 = 0.68, root mean square error (RMSE) = 7.51 kg ha−1 yr−1) compared with the original RF model (R2 = 0.52, RMSE = 8.99 kg ha−1 yr−1). Based on the improved model, it predicted that the highest and lowest S deposition flux were mainly concentrated on the Southeast China (69.57 kg S ha−1 yr−1) and Inner Mongolia (42.37 kg S ha−1 yr−1), respectively. The estimated wet S deposition flux displayed the remarkably seasonal variation with the highest value in summer (22.22 kg S ha−1 sea−1), follwed by ones in autumn (18.30 kg S ha−1 sea−1), spring (16.27 kg S ha−1 sea−1), and the lowest one in winter (14.71 kg S ha−1 sea−1), which was closely associated with the rainfall amounts. The study provides a novel approach for the S deposition estimation at a national scale.

(Invited) Passivation of High K/GaN Interfaces for GaN Tunnel FETs

A combined wet and dry cleaning process for GaN(0001) has been investigated with XPS, capacitance voltage measurement. Capacitance–voltage characterization showed that combined ex-situ wet sulfide passivation and in-situ cyclic trimethylaluminum (TMA)/hydrogen plasma exposure led to reductions in the densities of both interface traps and border traps. In situ XPS studies show that after the wet sulfur treatment on GaN(0001), sulfur desorbs in vacuum at 25C prior to gate oxide deposition. Ex-situ depth profiling ARXPS post-ALD deposition shows that the a-Al2O3 gate oxide bonds directly to the GaN substrate leaving both the gallium surface atoms and the oxide interfacial atoms with bulk-like charge. DFT calculations predict that the oxide/GaN(0001) interface will have bulk-like charges and a low density of band gap states. This passivation is consistent with the oxide restoring the surface gallium atoms to tetrahedral bonding by eliminating the gallium empty dangling bonds on bulk terminated GaN(0001). A key application of gate oxide on GaN is GaN tunnel FETs. Tunneling FETs (TFETs) are one promising option for reducing power consumption per logic function due to their potential for subthreshold slopes steeper than the thermionic limit of 60 mV/decade. While TFETs based on narrow-gap semiconductors have been demonstrated, the narrow band gaps of these materials also lead to limited on-off current ratios, compromising their power efficiency. GaN-based TFETs offer a potential solution to this problem, since the large band gap effectively reduces off-state current, and the large polarization fields present in III-N heterostructures (which arise from the lack of inversion symmetry in the wurtzite crystal structure of the III-N system)—and GaN/InGaN/GaN heterojunctions in particular—can be used to dramatically increase tunneling currents (and thus TFET on-state currents). However, implementation of a GaN-based TFET required a low defect gate oxide/GaN interface. This has been achieved using the two-step wet-dry surface passivation.

Comparative study of wet sulfur passivation process on GaSb (100) surface

ABSTRACTA comparative study for the pristine and sulfur passivated surfaces of gallium antimonide (GaSb) grown using molecular beam epitaxy is presented with the results recorded through X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) techniques. The as-grown GaSb surfaces were treated separately with 20% aqueous ammonium sulphide, ((NH4)2S), at 60°C for 10 m, aqueous sodium sulfide nonahydrate (Na2S.9H2O) with molarity 1 for 4 m at room temperature and base-thioacetamide (base-TAM) with molarity 0.18 for 40 m at 70°C. AFM topography shows the formation of very clean and flat surface for base-TAM treated GaSb. XPS results reveal lowest concentration of Ga2O3for GaSb surface treated with base-TAM.

The composition, seasonal variation, and potential sources of the atmospheric wet sulfur (S) and nitrogen (N) deposition in the southwest of China.

The composition, seasonal variation, and potential sources of sulfate (S) and nitrogen (N) deposition in precipitation in the southwest of China from 2003 to 2013 were investigated. The results showed that the concentration of SO4 (2-), NO3 (-), and NH4 (+) in rainwater were 10.57-1360, 7.16-523.71, and 7.54-1020 μeq l(-1), with an annual volume-weighted mean (VWM) concentration of 103.99, 46.73, and 97.30 μeq l(-1), respectively. The annual wet deposition of SO4 (2-), NO3 (-), and NH4 (+) was 21.66, 8.16, and 17.49 kg S (N) ha(-1), respectively. The temporal variations of the ions showed that the abrupt decreasing breakpoints were in 2008 for SO4 (2-) and in 2009 for NO3 (-) and NH4 (+), and increasing trends were observed after 2010 for the three ions. These trends reflected the effect of economy recession and the policy of controlling SO2 and NOx emissions. The acid rain type of precipitation was shifted from sulfur to a mixed one. The ions of SO4 (2-), NO3 (-), and NH4 (+) presented high values in winter and spring and low values in autumn and summer. A highly positive linear correlation between SO4 (2-) and NO3 (-) (R(2) = 0.71), SO4 (2-) and NH4 (+) (R(2) = 0.74), and NO3 (-) and NH4 (+) (R(2) = 0.84) existed while a strong negative correlation was found between the three main ionic concentrations and precipitation. The SO4 (2-) was mainly from fossil fuel combustion (60.53%), aged sea salt (19.03%), agriculture (11.38%), crust (6.66%), and biomass burning (2.40%); the NO3 (-) was mainly from fossil fuel combustion (75.41%), biomass burning (9.67%), aged sea salt (7.97%), and agriculture (6.96%); and the NH4 (+) was mainly from agriculture (86.38%), fossil fuel combustion (10.52%), and aged sea salt (3.09%).

Preparation of gallium nitride surfaces for atomic layer deposition of aluminum oxide.

A combined wet and dry cleaning process for GaN(0001) has been investigated with XPS and DFT-MD modeling to determine the molecular-level mechanisms for cleaning and the subsequent nucleation of gate oxide atomic layer deposition (ALD). In situ XPS studies show that for the wet sulfur treatment on GaN(0001), sulfur desorbs at room temperature in vacuum prior to gate oxide deposition. Angle resolved depth profiling XPS post-ALD deposition shows that the a-Al2O3 gate oxide bonds directly to the GaN substrate leaving both the gallium surface atoms and the oxide interfacial atoms with XPS chemical shifts consistent with bulk-like charge. These results are in agreement with DFT calculations that predict the oxide/GaN(0001) interface will have bulk-like charges and a low density of band gap states. This passivation is consistent with the oxide restoring the surface gallium atoms to tetrahedral bonding by eliminating the gallium empty dangling bonds on bulk terminated GaN(0001).

Wet sulfur passivation of GaSb(1 0 0) surface for optoelectronic applications

A comparative analysis of the properties of the non-passivated and S-passivated GaSb(1 0 0) surfaces has been performed through PL, AFM and RHEED characterization. The samples treated with a 1 M Na 2S aqueous solution demonstrate an increase in the 5 K PL intensity. According to AFM data, the annealing of the S-passivated GaSb(1 0 0) leads to the formation of the clean flat (1 0 0) surface. Moreover, after annealing the PL intensity of the S-passivated GaSb(1 0 0) surfaces decreases by 20%, whereas for the non-passivated samples it drops by more than a factor of 4. The method of wet sulfur passivation has shown great effectiveness in pre-epitaxial processing for LPE and MBE growth of the GaSb-related materials for optoelectronics.

An investigation into the use of ionizing radiation for the destruction of sulphur mustard

Chemical warfare agents have been stockpiled for almost a decade and their destruction has become an environmental issue that will continue to require attention for many years. There are hundreds of thousands of tonnes yet to be destroyed, and the current chemical or incineration techniques are not without problems. While many researchers are seeking better chemical techniques, we decided to try ionizing radiation to destroy sulphur mustard with the goal of producing non-toxic products. We irradiated a variety of sulphur mustard samples by both a mixed field source (β, γ and neutrons) and a pure gamma source. The mixed field irradiation of wet sulphur mustard for long irradiation times was the most successful at destroying the chemical agent.

Wet deposition of non sea-salt sulphate in the United Kingdom: The influence of natural sources

Because of its position to the west of Europe, much of the wet sulphur deposition in the west of the UK is background in the sense that it is not attributable to pollutants emitted within Europe less than four days previously. There are both natural and anthropogenic sources of this sulphur. An important natural source, especially during the summer, is dimethylsulphide (DMS) produced by marine phytoplankton. To identify the contribution of marine biogenic sulphur we have measured stable sulphur isotope ratios in precipitation. We show that biogenic sulphur is significant in summer but contributes little in winter and that around 5–10% of the annual background wet sulphur deposition is due to biogenic sources. During July and December 1993, airflow across the UK was predominantly westerly. The measured biogenic component of precipitation sulphate accounted for around 30 % of background sulphate in July but was negligible in December. Investigation of five day back-trajectories for the period indicated little opportunity for re-circulation of European emissions, suggesting that other (non-DMS) natural sources and non-European anthropogenic emissions were responsible for most of the background sulphur.

Assessment of wet sulphur deposition over the former USSR

Assessment of wet sulphur deposition over the former USSR

Assessment of wet sulphur deposition over the former USSR

The data obtained by different national and international networks of precipitation chemistry monitoring the territory of the former Soviet Union (FSU) have been generalized. Analyses of long-term trends of sulphur concentrations in precipitation for a 30-year period showed that the changes did not correlate with the dynamics of anthropogenic sulphur emissions into the atmosphere both over the FSU territory and Europe as a whole. Sulphur concentrations in precipitation reveal an obvious seasonal dependence with the spring maximum while deposition intensity has its maximum during summer time. All the FSU territory has been divided into 20 regions, and the mean values of sulphur concentration in precipitation and wet deposition have been estimated for each of them. The highest values were characteristic of the south-western part of the country and lowest ones of the remote areas of NorthEast. In the 80s, about 6.0 Tg of sulphur were annually wet deposited over the European territory of the FSU, about 3.0 Tg over the territory of Kazahstan and Central Asia, about 5.7 Tg in Siberia and the Russian Far East. The total wet sulphur deposition made up 60–90% of the anthropogenic sulphur emissions into the FSU atmosphere. DOI: 10.1034/j.1600-0889.1994.t01-2-00004.x

Wet deposition monitoring and modelling in New Brunswick — An area dominated by wet deposition due to long-range transport

Abstract Two wet deposition monitoring networks, the Coleson Cove Precipitation Monitoring Network (CCPMN) (12 stations) located in the Coleson Cove-Saint John area of south New Brunswick, and the Expanded New Brunswick Precipitation Monitoring Network (ENBPMN) (6 stations) covering the remainder of the province, were established in May 1988. The monitoring networks and a complementary modelling study were implemented to assess the relative contributions of local and distant sources to wet deposition in New Brunswick. Quality assurance/quality control activities for the networks included independent external audits, collocated samplers at one site and comparisons of weekly measurements at the ENBPMN sampler and the Canadian Air and Precipitation Monitoring Network (CAPMoN) sampler which makes daily measurements. The intercomparisons provided reassurance that the networks provided high quality data. Analysis of 2 years (June 1988–May 1990) data from the networks included routine statistical analyses for acid rain chemistry as well as analysis of 1 year of daily back trajectory data from Harcourt, New Brunswick. Three-day back trajectories determined at 12-h intervals from Harcourt on days with precipitatio showed that air masses originate mainly from regions in Quebec, Ontario and northeast U.S.A. which are known to have high sulphur oxide emissions. Some 18 trajectories were associated with 50% of the wet sulphate deposition and over 200 trajectories with 75% of the deposition in the 1-year period ending 31 May 1989. The MESOPUFF model, applied to an 800 km by 800 km domain that included the entire province of New Brunswick, was used to make predictions of wet sulphate and nitrate deposition at each of the wet deposition monitoring stations for a 2-year period, 1 June 1988-31 May 1990. Model predictions averaged over all receptors due to all sources in the model domain accounted for 7–25% of the measured seasonal average wet sulphate deposition and less than 3% of the measured wet nitrate deposition at all monitoring stations. Wet deposition in New Brunswick is thus dominated by distant sources through long-range transport. The model estimated that the oil-fired Coleson Cove thermal generating station contributed between 7% and 16% to the seasonal wet sulphur deposition and less than 3% of the seasonal wet nitrogen deposition at monitoring stations in the Coleson Cove-Saint John area. The estimates for wet nitrogen deposition are limited by the NO χ emissions information which is considered less reliable than SO 2 emissions information.

Coupling of wet scavenging of sulphur to clouds in a numerical weather prediction model

The in-cloud conversion of SO 2 to sulphate is an important part of the modelling of sulphur dispersion. The description of this process requires a coupling to meteorological processes in particular clouds and precipitation. In this study, the description of bulk wet scavenging is coupled to clouds and precipitation in a weather prediction model. Results are shown for summer, autumn and winter episodes of regional scale wet sulphur deposition over Scandinavia. We find that the liquid-phase formation of sulphate is in all cases comparable to the uptake of sulphate through cloud condensation nuclei. Sub-cloud scavenging by precipitation is small. The formation of sulphate through liquid reaction between SO 2 and ozone is small for the summer simulation where the hydrogen peroxide concentrations was chosen equal to 1 ppb, but important for the winter case with large-scale stratiform precipitation and hydrogen peroxide level of 0.25 ppb. The study indicates that the wet deposition is particularly sensitive to the initial hydrogen peroxide concentrations and subgrid mixing of hydrogen peroxide. Comparison with surface measurements show realistic patterns of sulphur concentrations in rain, and that most concentrations are within a factor of two of the measurements. DOI: 10.1034/j.1600-0889.1993.00001.x