Dry Deposition Of SO2 Research Articles

Trend of SO2 Gas Dry Deposition in Vietnam

This research used the calculating method of dry deposition to estimate SO2 dry deposition value and evaluate its trend in 5 recent years. The results indicate that SO2 emission at Northern sites is more changing than Southern ones in months by affecting meteorology and weather. Summer and autumn seasons have SO2 emitted concentrations higher than other seasons in 2019, 2020, and 2022 year at Yen Bai, Hoa Binh, and Ha Noi stations. The 2021 year has the highest SO2 dry deposition and the 2019 year has the lowest SO2 dry deposition in 5 recent years. The Hanoi site has the highest SO2 dry deposition value from 2019 to 2022 year. Hoa Binh site has the highest SO2 dry deposition at 2.45 kg/ha/year in 2023. High SO2 dry deposition occurs normally in the summer and autumn (from April to August). Southern sites have lower SO2 dry deposition amounts with not much change than the Northern sites of Vietnam. The increasing trend of SO2 dry deposition happened from 1999 to 2023 year and it increases sharply from 1999 to 2021. Therefore, SO2 dry deposition will have a light-increasing trend in the future.

UKESM1.1: development and evaluation of an updated configuration of the UK Earth System Model

Abstract. Many Coupled Model Intercomparison Project phase 6 (CMIP6) models have exhibited a substantial cold bias in the global mean surface temperature (GMST) in the latter part of the 20th century. An overly strong negative aerosol forcing has been suggested as a leading contributor to this bias. An updated configuration of UK Earth System Model (UKESM) version 1, UKESM1.1, has been developed with the aim of reducing the historical cold bias in this model. Changes implemented include an improved representation of SO2 dry deposition, along with several other smaller modifications to the aerosol scheme and a retuning of some uncertain parameters of the fully coupled Earth system model. The Diagnostic, Evaluation and Characterization of Klima (DECK) experiments, a six-member historical ensemble and a subset of future scenario simulations are completed. In addition, the total anthropogenic effective radiative forcing (ERF), its components and the effective and transient climate sensitivities are also computed. The UKESM1.1 preindustrial climate is warmer than UKESM1 by up to 0.75 K, and a significant improvement in the historical GMST record is simulated, with the magnitude of the cold bias reduced by over 50 %. The warmer climate increases ocean heat uptake in the Northern Hemisphere oceans and reduces Arctic sea ice, which is in better agreement with observations. Changes to the aerosol and related cloud properties are a driver of the improved GMST simulation despite only a modest reduction in the magnitude of the negative aerosol ERF (which increases by +0.08 W m−2). The total anthropogenic ERF increases from 1.76 W m−2 in UKESM1 to 1.84 W m−2 in UKESM1.1. The effective climate sensitivity (5.27 K) and transient climate response (2.64 K) remain largely unchanged from UKESM1 (5.36 and 2.76 K respectively).

Long-term declines in atmospheric nitrogen and sulfur deposition reduce critical loads exceedances at multiple Canadian rural sites, 2000–2018

Abstract. Daily air concentrations of inorganic nitrogen (N) species, including gaseous HNO3 and particulate-bound (p)NH4+ and pNO3-, and sulfur (S) species, including SO2 and pSO42-, and precipitation concentrations of NO3-, NH4+, and SO42-, have been routinely monitored by the Canadian Air and Precipitation Monitoring Network (CAPMoN) since 1983. Data at 15 rural sites from 2000–2018 were used to estimate dry and wet N and S deposition fluxes, which were then used to explore their spatiotemporal trends and assess ecosystem damage through a retrospective analysis of critical loads (CLs) exceedances. Total (dry + wet) N deposition ranged from 1.7–9.5 kgNha-1yr-1 among the 15 sites, though dry deposition of NH3 and some oxidized N species were not included due to lack of monitoring data. Based on additional N measurements in 2010 at one of the sites, annual total N deposition may be underestimated by up to 32 %. Total N deposition was dominated by wet NO3- and wet NH4+ deposition, which together comprised 71 %–95 %. Contributions to dry N deposition were 40 %–74 % by HNO3, 11 %–40 % by pNH4+, and 5 %–25 % by pNO3-. Total S deposition ranged from 1.3–8.5 kgSha-1yr-1 and was dominated by wet deposition of SO42- and dry deposition of SO2. Relative percentages of wet and dry S deposition were 45 %–89 % and 11 %–55 %, respectively. Acidic ion fluxes were greatest in southeastern Canada and were comparable among the west coast, prairie, remote, and eastern Canadian sites. Oxidized N (dry HNO3, dry pNO3-, wet NO3-) deposition was greater than that of reduced N (dry pNH4+, wet NH4+) in the early 2000s. In 2014–2018, reduced N deposition surpassed that of oxidized N in southeastern Canada. Total N and S deposition decreased significantly at a rate of −0.03 to −0.25 kgNha-1yr-1 (−1.1 % yr−1 to −3.3 % yr−1) and −0.08 to −0.66 kgSha-1yr-1 (−3.5 % yr−1 to −6.6 % yr−1), respectively, among the sites. The weak declining trend in total N deposition at the west coast site was consistent with the slower decline in NOx emissions in western Canada. Reductions in total N deposition were driven by its oxidized form as trends in reduced N were non-significant. As a result, reduced N contributions to total N deposition increased on average from 42 % in 2000–2004 to 53 % in 2014–2018. Anthropogenic NOx and SO2 emissions reductions in both eastern Canada and eastern US were highly effective in reducing total oxidized N and total S deposition, respectively, in eastern Canada. Acidic deposition exceeded terrestrial CL at 5 of the 14 sites and aquatic CL at 2 of the 5 sites in the early 2000s. However, exceedances have been trending downwards and acidic deposition fluxes were mostly near or below CL after 2012 for the subset of sites assessed, which support recovery from historical acidification. Further assessments of CL exceedances are required in other Canadian regions susceptible to acidification and affected by elevated or increasing N and S emissions.

Sulfur deposition in the Beijing-Tianjin-Hebei region, China: Spatiotemporal characterization and regional source attributions

Elevated atmospheric sulfur (S) deposition, which can affect ecosystems and human health, is a severe environment problem in the Beijing-Tianjin-Hebei (BTH) region. Here we investigated the spatiotemporal characteristics of S deposition and its regional sources in January (winter) and July (summer), 2015 in BTH using the CMAQ model coupled with the Integrated Source Apportionment Method (CMAQ-ISAM). The results showed that S deposition in high ecological risk areas (regions with S deposition significantly exceeding the critical load) of BTH was higher in summer (1.99 kg S ha−1 mon−1) than in winter (1.18 kg S ha−1 mon−1), with 82% (18% for winter) attributed to wet deposition and the rest to dry deposition. The daily variation of S dry deposition was mainly dependent on sulfur dioxide (SO2) dry deposition velocity in winter while S concentration in summer. SO2 dry deposition velocity was mainly caused by the change of resistance to surface resistance (Rc). In summer, during the periods of significant wet deposition due to precipitation, S concentration decreased significantly by ∼70%. The results of the regional source appointment suggested that local emissions (inside BTH) contributed ∼65% to dry deposition but only 8% and 28% to wet deposition in January and July respectively. For the contribution from non-local emission (outside BTH), Shandong contributed most to S dry deposition (17% on average). The contributions from Shandong (23%) and Shanxi (12%) to S wet deposition were higher in July than in January (10% and 3%, respectively). Analysis of daily contributions suggests that the contribution from non-local emissions to dry deposition could be enhanced by the southwest background wind. Local emissions took an important part in S total deposition (∼70%) during dry days while non-local emissions contributed significantly (∼65%) to total deposition during wet days. For seasonally, S total deposition was contributed more by local emissions (56%) in January but was dominated by non-local emissions (65%) in July. It demonstrates the need for a comprehensive strategy on local and non-local emissions for pollutant control against ecological risk caused by deposition.

Evaluation of SO<sub>2</sub>, SO<sub>4</sub><sup>2−</sup> and an updated SO<sub>2</sub> dry deposition parameterization in the United Kingdom Earth System Model

Abstract. In this study we evaluate simulated surface SO2 and sulfate (SO42-) concentrations from the United Kingdom Earth System Model (UKESM1) against observations from ground-based measurement networks in the USA and Europe for the period 1987–2014. We find that UKESM1 captures the historical trend for decreasing concentrations of atmospheric SO2 and SO42- in both Europe and the USA over the period 1987–2014. However, in the polluted regions of the eastern USA and Europe, UKESM1 over-predicts surface SO2 concentrations by a factor of 3 while under-predicting surface SO42- concentrations by 25 %–35 %. In the cleaner western USA, the model over-predicts both surface SO2 and SO42- concentrations by factors of 12 and 1.5 respectively. We find that UKESM1’s bias in surface SO2 and SO42- concentrations is variable according to region and season. We also evaluate UKESM1 against total column SO2 from the Ozone Monitoring Instrument (OMI) using an updated data product. This comparison provides information about the model's global performance, finding that UKESM1 over-predicts total column SO2 over much of the globe, including the large source regions of India, China, the USA, and Europe as well as over outflow regions. Finally, we assess the impact of a more realistic treatment of the model's SO2 dry deposition parameterization. This change increases SO2 dry deposition to the land and ocean surfaces, thus reducing the atmospheric loading of SO2 and SO42-. In comparison with the ground-based and satellite observations, we find that the modified parameterization reduces the model's over-prediction of surface SO2 concentrations and total column SO2. Relative to the ground-based observations, the simulated surface SO42- concentrations are also reduced, while the simulated SO2 dry deposition fluxes increase.

Declining dry deposition of NO2 and SO2 with diverse spatiotemporal patterns in China from 2013 to 2018

The nitrogen and sulfur deposition results in damages on ecosystems, while the lack of direct observation on dry deposition limits our understanding of the total deposition. This study aimed to improve the methodology and estimates of NO2 and SO2 dry deposition in China and to explore the efficacy of China's recent emission control measures on dry deposition at the national and regional scales. We combined the random forest algorithm and the GEOS-Chem chemical transport model to predict the dry deposition fluxes of NO2 and SO2 and their inter-annual variabilities during 2013–2018 in mainland China. The annual NO2 dry deposition ranged between 2.1 and 3.1 kg N ha−1 yr−1, with an annual reduction rate of 0.21 kg N ha−1 yr−1 over this period. The areas with large deposition were located in the east, while the biggest reduction existed in the relatively clean Tibet Plateau region. The annual SO2 dry deposition ranged between 7.5 and 18.4 kg S ha−1 yr−1, with the annual reduction rate at 2.4 kg S ha−1 yr−1. Both the magnitude and relative reduction in the north were generally larger than the south. Regarding the four typical economically developed regions, the NO2 deposition declined slower than the national average, while SO2 generally declined faster than or equivalently to the national average, except for Pearl River Delta. The reduced emissions attributed to the national action on air pollution control were identified as an important reason for the declining deposition. However, the increased traffic and industrial capacity in the east weakened its benefit on NO2.

Impacts of transportation sector emissions on future U.S. air quality in a changing climate. Part II: Air quality projections and the interplay between emissions and climate change

In Part II of this work we present the results of the downscaled offline Weather Research and Forecasting/Community Multiscale Air Quality (WRF/CMAQ) model, included in the “Technology Driver Model” (TDM) approach to future U.S. air quality projections (2046–2050) compared to a current-year period (2001–2005), and the interplay between future emission and climate changes. By 2046–2050, there are widespread decreases in future concentrations of carbon monoxide (CO), nitrogen oxides (NOx = NO + NO2), volatile organic compounds (VOCs), ammonia (NH3), sulfur dioxide (SO2), and particulate matter with an aerodynamic diameter ≤ 2.5 μm (PM2.5) due mainly to decreasing on-road vehicle (ORV) emissions near urban centers as well as decreases in other transportation modes that include non-road engines (NRE). However, there are widespread increases in daily maximum 8-hr ozone (O3) across the U.S., which are due to enhanced greenhouse gases (GHG) including methane (CH4) and carbon dioxide (CO2) under the Intergovernmental Panel on Climate Change (IPCC) A1B scenario, and isolated areas of larger reduction in transportation emissions of NOx compared to that of VOCs over regions with VOC-limited O3 chemistry. Other notable future changes are reduced haze and improved visibility, increased primary organic to elemental carbon ratio, decreases in PM2.5 and its species, decreases and increases in dry deposition of SO2 and O3, respectively, and decreases in total nitrogen (TN) deposition. There is a tendency for transportation emission and CH4 changes to dominate the increases in O3, while climate change may either enhance or mitigate these increases in the west or east U.S., respectively. Climate change also decreases PM2.5 in the future. Other variable changes exhibit stronger susceptibility to either emission (e.g., CO, NOx, and TN deposition) or climate changes (e.g., VOC, NH3, SO2, and total sulfate deposition), which also have a strong dependence on season and specific U.S. regions.

Ship emissions and the use of current air cleaning technology: contributions to air pollution and acidification in the Baltic Sea

Abstract. The shipping sector is a significant contributor to emissions of air pollutants in marine and coastal regions. In order to achieve sustainable shipping, primarily through new regulations and techniques, greater knowledge of dispersion and deposition of air pollutants is required. Regional model calculations of the dispersion and concentration of sulfur, nitrogen, and particulate matter, as well as deposition of oxidized sulfur and nitrogen from the international maritime sector in the Baltic Sea and the North Sea, have been made for the years 2011 to 2013. The contribution from shipping is highest along shipping lanes and near large ports for concentration and dry deposition. Sulfur is the most important pollutant coupled to shipping. The contribution of both SO2 concentration and dry deposition of sulfur represented up to 80 % of the total in some regions. WHO guidelines for annual concentrations were not trespassed for any analysed pollutant, other than PM2.5 in the Netherlands, Belgium, and central Poland. However, due to the resolution of the numerical model, 50 km × 50 km, there may be higher concentrations locally close to intense shipping lanes. Wet deposition is more spread and less sensitive to model resolution. The contribution of wet deposition of sulfur and nitrogen from shipping was up to 30 % of the total wet deposition. Comparison of simulated to measured concentration at two coastal stations close to shipping lanes showed some underestimations and missed maximums, probably due to resolution of the model and underestimated ship emissions. A change in regulation for maximum sulfur content in maritime fuel, in 2015 from 1 to 0.1 %, decreases the atmospheric sulfur concentration and deposition significantly. However, due to costs related to refining, the cleaning of exhausts through scrubbers has become a possible economic solution. Open-loop scrubbers meet the air quality criteria but their consequences for the marine environment are largely unknown. The resulting potential of future acidification in the Baltic Sea, both from atmospheric deposition and from scrubber water along the shipping lanes, based on different assumptions about sulfur content in fuel, scrubber usage, and increased shipping density has been assessed. The increase in deposition for different shipping and scrubber scenarios differs for the basins in the Baltic Sea, with highest potential of acidification in the southern basins with high traffic. The proportion of ocean-acidifying sulfur from ships increases when taking scrubber water into account and the major reason for increasing acidifying nitrogen from ships is increasing ship traffic. Also, with the implementation of emission control for nitrogen, the effect of scrubbers on acidification is evident. This study also generates a database of shipping and scrubber scenarios for atmospheric deposition and scrubber exhaust from the period 2011 to 2050.

Mapping recession risk for cultural heritage stone in Mexico City due to dry and wet deposition of urban air pollutants

Air pollution is a threat to cultural heritage because it accelerates the natural deterioration of monuments, palaces, churches, and archaeological ruins, which have an irreplaceable value. In the Mexico City Metropolitan Area (MCMA), there are 19 968 buildings registered as archaeological, historic, or artistic monuments. Some are built with calcareous rocks (limestone and marble) but many of them are made with andesite, tezontle and tuff stone. This paper reports for the first time the spatial distribution of the potential risk of deterioration on calcareous rocks in terms of surface recession with regard to Mexican cultural heritage in the MCMA for the base year 2007. The risk estimate was performed using Lipfert’s damage function, only applicable to carbonate stones of medium and low porosity. These include mainly medium/high density limestone and marble. Carrara white marble has a density of 2.69 g cm –3 and a porosity of 0.37%, and limestone has a density of 2.2-2.6 g cm –3 and a porosity of 5-20%. For high porosity (low density) limestone the function would be applicable with a potential under-estimation. In this function, annual recession rate is a function of annual averages of precipitation, pH, and dry deposition of SO 2 and HNO 3 . Data from several meteorological monitoring networks, the MCMA air quality and acid deposition monitoring networks, and a 3D air quality model (MCCM) were interpolated in a GIS in order to obtain map layers for these variables. These overlaid maps were used to apply the Lipfert functions at the specific coordinates of a small sample of relevant historic or artistic monuments. The complexity of climate gradients, wind patterns, and emissions distribution within the Mexico Megacity leads to gradients as large as 50% in estimated recession rates using the Lipfert function at nearby sites made of the same type of building materials. The Comision Ambiental de la Megalopolis (Environmental Commission of the Megacity) divides the MCMA into five sectors. Differences in recession rates between them were, in 1990, as large as those between estimated values for Oviedo, Paris, and Prague in Europe for the period 1980-2000. Recession rates decreased by about 50% from 1990 to 2007, the base year for this report, due to the success of air pollution control actions focused on the protection of public health. Nevertheless, strong recession gradients are still expected for carbonate stone within the MCMA. The recession values reported in this work must be taken as conservative estimates due to the not yet optimal performance of 3D air quality models in urban meteorology and the high degree of uncertainty in modeling emissions inventories. Most notable is the SO 2 emissions inventory. These maps call for a program of experimental determination of recession rates for building materials that comprise a very large part of Mexico’s unique cultural heritage. These maps should also be added to the critical level maps obtained for human exposure, crops, and ecosystems in order to properly estimate the actual cost of air pollution in the MCMA and the area under its influence.

Contribution of ship emissions to the concentration and deposition of air pollutants in Europe

Abstract. Emissions from the marine transport sector are one of the least-regulated anthropogenic emission sources and contribute significantly to air pollution. Although strict limits were introduced recently for the maximum sulfur content in marine fuels in the SECAs (sulfur emission control areas) and in EU ports, sulfur emissions outside the SECAs and emissions of other components in all European maritime areas have continued to increase in the last two decades. We have used the air quality model CAMx (Comprehensive Air Quality Model with Extensions) with and without ship emissions for the year 2006 to determine the effects of international shipping on the annual as well as seasonal concentrations of ozone, primary and secondary components of PM2.5, and the dry and wet deposition of nitrogen and sulfur compounds in Europe. The largest changes in pollutant concentrations due to ship emissions were predicted for summer. Concentrations of particulate sulfate increased due to ship emissions in the Mediterranean (up to 60 %), the English Channel and the North Sea (30–35 %), while increases in particulate nitrate levels were found especially in the north, around the Benelux area (20 %), where there were high NH3 land-based emissions. Our model results showed that not only are the atmospheric concentrations of pollutants affected by ship emissions, but also depositions of nitrogen and sulfur compounds increase significantly along the shipping routes. NOx emissions from the ships, especially in the English Channel and the North Sea, cause a decrease in the dry deposition of reduced nitrogen at source regions by moving it from the gas phase to the particle phase which then contributes to an increase in the wet deposition at coastal areas with higher precipitation. In the western Mediterranean region, on the other hand, model results show an increase in the deposition of oxidized nitrogen (mostly HNO3) due to the ship traffic. Dry deposition of SO2 seems to be significant along the shipping routes, whereas sulfate wet deposition occurs mainly along the Scandinavian and Adriatic coasts. The results presented in this paper suggest that evolution of NOx emissions from ships and land-based NH3 emissions will play a significant role in future European air quality.

Dry deposition of O3 and SO2 estimated from gradient measurements above a temperate mixed forest

Vertical profiles of O3 and SO2 concentrations were monitored at the Borden Forest site in southern Ontario, Canada from May 2008 to April 2013. A modified gradient method (MGM) was applied to estimate O3 and SO2 dry deposition fluxes using concentration gradients between a level above and a level below the canopy top. The calculated five-year mean (median) dry deposition velocity (Vd) were 0.35 (0.27) and 0.59 (0.54) cm s−1, respectively, for O3 and SO2. Vd(O3) exhibited large seasonal variations with the highest monthly mean of 0.68 cm s−1 in August and the lowest of 0.09 cm s−1 in February. In contrast, seasonal variations of Vd(SO2) were smaller with monthly means ranging from 0.48 (May) to 0.81 cm s−1 (December). The different seasonal variations between O3 and SO2 were caused by the enhanced SO2 uptake by snow surfaces in winter. Diurnal variations showed a peak value of Vd in early morning in summer months for both O3 and SO2. Canopy wetness increased the non-stomatal uptake of O3 while decreasing the stomatal uptake. This also applied to SO2, but additional factors such as surface acidity also played an important role on the overall uptake.

Trends of deposition fluxes and loadings of sulfur dioxide and nitrogen oxides in the artificial Three Northern Regions Shelter Forest across northern China

This study provides the first estimate of dry deposition fluxes of criteria air pollutants (SO2 and NOx) across the Three Northern Regions Shelter Forest (TNRSF) region in Northern China and their long-term trends from 1982 to 2010 using the inferential method. Dry deposition velocities of SO2 and NOx increased in many places of the TNRSF up to 118.2% for SO2 and 112.1% for NOx over the last three decades due to the increased vegetation coverage over the TNRSF. The highest atmospheric deposition fluxes of SO2 and NOx were found in the Central-North China region, followed by the Northeast and the Northwest China regions of the TNRSF. A total of 820,000 t SO2 and 218,000 t NOx was estimated to be removed from the atmosphere through dry deposition process over the TNRSF from 1982 to 2010. About 50% of the total removal occurred in the Central-North China region. The estimated total SO2 and NOx dry deposition fluxes from 1982 to 2010 between a TNRSF site in this region and an adjacent farmland outside the TNRSF showed that the fluxes of these two chemicals at the TNRSF site were the factors of 2–3 greater than their fluxes in the farmland.

An evaluation of simulated particulate sulfate over East Asia through global model intercomparison

AbstractSulfate aerosols simulated by an aerosol module coupled to the Nonhydrostatic Icosahedral Atmospheric Model (NICAM) at a spatial resolution (220 km) widely used by global climate models were evaluated by a comparison with in situ observations and the same aerosol module coupled to the Model for Interdisciplinary Research on Climate (MIROC) over East Asia for January, April, July, and October 2006. The results indicated that a horizontal gradient of sulfate from the source over China to the outflow over Korea‐Japan was present in both the simulations and the observations. At the observation sites, the correlation coefficients of the sulfate concentrations between the simulations and the observations were high (NICAM: 0.49–0.89, MIROC: 0.61–0.77), whereas the simulated sulfate concentrations were lower than those obtained by the observation with the normalized mean bias of NICAM being −68 to −54% (all), −77 to −63% (source), and −67 to −30% (outflow) and that of MIROC being −61 to −28% (all), −77 to −63% (source), and −60 to +2% (outflow). Both NICAM and MIROC strongly underpredict surface SO2 over China source regions and Korea‐Japan outflow regions, but the MIROC SO2 is much higher than NICAM SO2 over both regions. These differences between the models were mainly explained by differences in the sulfate formation within clouds and the dry deposition of SO2. These results indicated that the uncertainty of the meteorological and cloud fields as well as the vertical transport patterns between the different host climate models has a substantial impact on the simulated sulfate distribution.

Global dry deposition of nitrogen dioxide and sulfur dioxide inferred from space‐based measurements

AbstractA method is developed to estimate global NO2 and SO2 dry deposition fluxes at high spatial resolution (0.1°×0.1°) using satellite measurements from the Ozone Monitoring Instrument (OMI) on the Aura satellite, in combination with simulations from the Goddard Earth Observing System chemical transport model (GEOS‐Chem). These global maps for 2005–2007 provide a data set for use in examining global and regional budgets of deposition. In order to properly assess SO2 on a global scale, a method is developed to account for the geospatial character of background offsets in retrieved satellite columns. Globally, annual dry deposition to land estimated from OMI as NO2 contributes 1.5 ± 0.5 Tg of nitrogen and as SO2 contributes 13.7 ± 4.0 Tg of sulfur. Differences between OMI‐inferred NO2 dry deposition fluxes and those of other models and observations vary from excellent agreement to an order of magnitude difference, with OMI typically on the low end of estimates. SO2 dry deposition fluxes compare well with in situ Clear Air Status and Trends Network‐inferred flux over North America (slope = 0.98, r = 0.71). The most significant NO2 dry deposition flux to land per area occurs in the Pearl River Delta, China, at 13.9 kg N ha−1 yr−1, while SO2 dry deposition has a global maximum rate of 72.0 kg S ha−1 yr−1 to the east of Jinan in China's Shandong province. Dry deposition fluxes are explored in several urban areas, where NO2 contributes on average 9–36% and as much as 85% of total NOy dry deposition.

Dry deposition of nitrogen compounds (NO<sub>2</sub>, HNO<sub>3</sub>, NH<sub>3</sub>), sulfur dioxide and ozone in west and central African ecosystems using the inferential method

Abstract. This work is part of the IDAF program (IGAC-DEBITS-AFRICA) and is based on the long-term monitoring of gas concentrations (1998–2007) established at seven remote sites representative of major African ecosystems. Dry deposition fluxes were estimated by the inferential method using on the one hand surface measurements of gas concentrations (NO2, HNO3, NH3, SO2 and O3) and on the other hand modeled exchange rates. Dry deposition velocities (Vd) were calculated using the big-leaf model of Zhang et al. (2003b). The bidirectional approach is used for NH3 surface–atmosphere exchange (Zhang et al., 2010). Surface and meteorological conditions specific to IDAF sites have been used in the models of deposition. The seasonal and annual mean variations of gaseous dry deposition fluxes (NO2, HNO3, NH3, O3 and SO2) are analyzed. Along the latitudinal transect of ecosystems, the annual mean dry deposition fluxes of nitrogen compounds range from −0.4 to −0.8 kg N ha−1 yr−1 for NO2, from −0.7 to −1.0 kg N ha−1 yr−1 for HNO3 and from −0.7 to −8.3 kg N ha−1 yr−1 for NH3 over the study period (1998–2007). The total nitrogen dry deposition flux (NO2+HNO3+NH3) is more important in forests (−10 kg N ha−1 yr−1) than in wet and dry savannas (−1.6 to −3.9 kg N ha−1 yr−1). The annual mean dry deposition fluxes of ozone range between −11 and −19 kg ha−1 yr−1 in dry and wet savannas, and −11 and −13 kg ha−1 yr−1 in forests. Lowest O3 dry deposition fluxes in forests are correlated to low measured O3 concentrations, lower by a factor of 2–3, compared to other ecosystems. Along the ecosystem transect, the annual mean of SO2 dry deposition fluxes presents low values and a small variability (−0.5 to −1 kg S ha−1 yr−1). No specific trend in the interannual variability of these gaseous dry deposition fluxes is observed over the study period.

Spatial distribution and temporal variations of atmospheric sulfur deposition in Northern China: insights into the potential acidification risks

Abstract. Atmospheric sulfur (S) deposition via precipitation, particles and gases was investigated at ten sites in Northern China. Measurements were performed continuously between December 2007 and November 2010. The total S deposition flux in the target area ranged from 35.0 to 100.7 kg S ha−1 yr−1, noticeably higher than the values documented in Europe, North America, and East Asia. The ten-site, 3-yr average total S deposition was 64.8 kg S ha−1 yr−1, with 68% attributed to dry deposition (mainly SO2) and the rest to wet deposition. Consequently, the spatial distribution of the total flux was consistent to that of dry deposition, that is, higher values were observed at industrial and urban sites than at agricultural and rural sites. However, the seasonal variation in the total S deposition was not obvious across the entire year because of opposite seasonal trends in wet and dry deposition. It was found that the wet deposition, without significant spatial and interannual differences, was influenced by the volume of precipitation, the air-column concentrations of S compounds and in-cloud scavenging. Similar to the wet deposition, the dry-deposited sulfate was also less dependent on the surface concentration. Nevertheless, the regional differences in SO2 dry deposition were mostly explained by the ambient concentration, which is closely associated with local emissions. As expected, the spatial pattern of total S deposition resembled that of the emission inventory, indicating the dramatic anthropogenic imprints on the regional S budget. Although at most of the study sites the "acid equivalents" deposition of S was comparable to that of nitrogen (N), the importance of S in the acidification risks was more pronounced at the industrial sites. The ten-site, 3-yr mean total "acid equivalents" deposition of S and N was estimated to be 8.4 (range: 4.2–11.6) keq ha−1 yr−1, which exceeds the critical loads for natural ecosystems in Northern China. Taking these findings and our previous studies together, a multi-pollutant perspective and joint mitigation strategies to abate SO2 and NH3 simultaneously in the target area are recommended to protect natural ecosystems from excess acid deposition.

A comparison of observed and parameterized SO2 dry deposition over a grassy clearing in Duke Forest

Deposition of trace gases, such as sulfur dioxide (SO 2 ), can affect plant and soil chemistry in different ecosystems. Measurements over a complex ecosystem, like a forest clearing, are necessary to determine more accurate deposition rates that can be used to improve parameterizations and models. The flux-gradient technique was used to determine SO 2 fluxes over grass in a clearing at Duke Forest, North Carolina, USA on 25 June – 2 July 2008. The mean flux was −0.037 ± 0.024 μg m −2 s −1 . Dew on the canopy enhanced the uptake of SO 2 , which increased deposition rates. Deposition velocities ( V d ) fluctuated greatly with a mean of 1.00 ± 0.48 cm s −1 . The large variation in V d was not fully captured by estimates determined from a multilayer model (MLM) and a big-leaf model (BLM). Mean deposition velocities derived from the MLM and BLM were 1.25 ± 0.21 cm s −1 and 0.63 ± 0.12 cm s −1 , respectively. The model estimations of V d in this study were probably affected by uncertainties associated with canopy resistance, particularly with stomatal and non-stomatal processes. ► Stomatal and non-stomatal resistances were significant contributors to canopy resistance for SO 2 deposition. ► Deposition rates increased when the canopy was wet with rain or dew. ► Deposition velocities from a multilayer model generally agreed with observed deposition velocities.

Sources, transport, and sinks of SO2 over the equatorial Pacific during the Pacific Atmospheric Sulfur Experiment

The Pacific Atmospheric Sulfur Experiment (PASE) is the first sulfur-budget field experiment to feature simultaneous flux measurements of DMS marine emissions and SO2 deposition to the ocean surface. We make use of these data to constrain a 1-D chemical transport model to study the production and loss pathways for DMS and SO2 over the equatorial Pacific. Model results suggest that OH is the main sink for DMS in the boundary layer (BL), and the average DMS-to-SO2 conversion efficiency is ~73%. In an exploratory run involving the addition of 1 pptv of BrO as a second oxidant, a 14% increase in the DMS flux is needed beyond that based on OH oxidation alone. This BrO addition also reduces the DMS-to-SO2 conversion efficiency from 73% to 60%. The possibility of non-DMS sources of marine sulfur influencing the estimated conversion efficiency was explored and found to be unconvincing. For BL conditions, SO2 losses consist of 48% dry deposition, while transport loss to the BuL and aerosol scavenging each account for another 19%. The conversion of SO2 to H2SO4 consumes the final 14%. In the BuL, cloud scavenging removes 85% of the SO2, thus resulting in a decreasing vertical profile for SO2. The average SO2 dry deposition velocity from direct measurements (i.e., 0.36 cm sec−1) is approximately 50% of what is calculated from the 1-D model and the global GEOS-Chem model. This suggests that the current generation of global models may be significantly overestimating SO2 deposition rates over some tropical marine areas. Although the specific mechanism cannot be determined, speculation here is that the dry deposition anomalous results may point to the presence of a micro-surface chemical phenomenon involving partial saturation with either S(IV) and/or S(VI) DMS oxidation products. This could also appear as a pH drop in the ocean’s surface microfilm layer in this region. Finally, we propose that the enhanced SO2 level observed in the lower free troposphere versus that in the upper BuL during PASE is most likely the result of transported DMS/SO2-rich free-tropospheric air parcels from the east of the PASE sampling area, rather than an inadequate representation in the model of local convection.

Effect of SO2 Dry Deposition on Porous Dolomitic Limestones

The present study is concerned with the assessment of the relative resistance of a monumental dolomitic limestone (Laspra – Spain) used as building material in stone monuments and submitted to artificial ageing by SO2 dry deposition in the presence of humidity. To investigate the protection efficiency of different polymeric coatings, three commercially available siloxane-based oligomers (Lotexan-N, Silres BS 290 and Tegosivin HL 100) and a newly synthesized hybrid nanocomposite with silsesquioxane units (TMSPMA) were used. A comparative assessment of the data obtained in this study underlines that a better limestone protection was obtained when treated with the hybrid nanocomposite with silsesquioxane units.

Evaluation of SO<SUB align=right>2 dry deposition over a cassava plantation in Rayong, Thailand

SO2 emissions have become a significant problem in the East Asian region. Long term exposure to high SO2 concentration can affect human health and the environment. Approximately half of the SO2 is delivered to the earth by the dry deposition process; the other half is deposited by wet deposition. Thus, an assessment of SO2 dry deposition is necessary for understanding its qualitative and quantitative effects. In the research program described here, SO2 dry deposition was studied in terms of SO2 dry deposition flux and deposition velocity using the Bowen ratio technique. All necessary parameters were measured above a cassava plantation at a site in Rayong, Thailand during the period from June to September 2004. The Bowen ratio technique was most applicable during the 8:00 to 17:00 time period of each day. The results yield an average transfer coefficient of 10.6 cm/s, relevant to the height interval across which differences were measured. The average dry deposition flux was 0.17 mg/m²/hr and the average dry deposition velocity was 0.14 cm/s.