Average Dry Deposition Fluxes Research Articles

Urban air PCDD/Fs: Dry deposition fluxes and mass transfer coefficients determined using a water surface sampler

Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) cause significant environmental concerns. Atmospheric PCDD/Fs permeate water bodies and other ecosystems through wet and dry deposition. In an urban site, dry deposition flux samples of gaseous phase PCDD/Fs were collected by a water surface sampler (WSS) operated between June 2022 and June 2023. There is a conspicuous absence of literature on the direct measurement of dry deposition flux levels in the gaseous phase of PCDD/Fs. In the study, PCDD/Fs in the gas phase reaching the WSS dissolved in the water according to Henry's Law. The PCDD/Fs in the water were transferred to an XAD-2 resin column, sorbing the dissolved PCDD/Fs. The average monthly gas phase dry deposition flux was 34.07 ± 9.35 pg/m2-day (7.35 ± 2.16 pg I-TEQ/m2-day). The highest flux was measured in March (49.53 pg/m2-day), and the lowest was in August (18.64 pg/m2-day). These values indicated the direct flux from air to water. The atmospheric concentration of the gas-phase ranged from 68.38 to 126.88 fg/m3 (13.22–25.01 fg I-TEQ/m3). Dry deposition fluxes and concentrations of atmospheric PCDD/Fs were bigger in the colder months than in the warmer months. This was probably due to a significant increase in residential heating during the colder months, decreased photochemical reactions, and lower mixing heights. Regarding congeners in the dry deposition flux and concentration values in I-TEQ units, 2,3,7,8-TCDD compound predominated with the proportions of 31.61 ± 7.76% and 29.09 ± 12.34%, respectively. Concurrently measured dry deposition flux (Fg) and ambient air concentration (Cg) of PCDD/Fs were considered in the determination of mass transfer coefficient (MTC = Fg/Cg) calculation for each PCDD/F congener. The average MTC for targeted 17 PCDD/Fs was 0.45 ± 0.15 cm/s, and it fluctuated between 0.89 ± 0.30 cm/s for 2,3,7,8-TCDF and 0.2 ± 0.16 cm/s for OCDD.

Characteristics of Cd Fluxe in Topsoil Around Typical Mining Area in Hezhou, Guangxi

Guangxi is a typical geological high background area in southwest China, where carbonates, black rock series, basic-ultrabasic rock mass, and metal deposits (mineralized bodies) exhibit strong weathering into loam, resulting in higher cadmium (Cd) content in the soil than that in other areas of China. In order to investigate the degree of influence of mining activities on topsoil environmental quality in the area with high geological background, we chose a mining area and control area in Hezhou for this research and systematically carried out a comparative study on Cd transport routes and transport flux density in topsoil. The results showed that the average atmospheric dry and wet deposition flux densities of Cd in the soil of the mining area and control area were 1.87 g·(hm2·a)-1 and 1.52 g·(hm2·a)-1, accounting for 61.5% and 60.3% of the total input flux density, respectively. The flux density of Cd in the soil by fertilization and irrigation was lower. Surface water infiltration was the main avenue of soil Cd output in both the mining area and control area, accounting for 75.4% and 86.6% of the total output flux density, respectively. The harvest output flux density in the mining area was higher than that in the control area, and the Cd content of rice planted in the mining area was higher than the standard, whereas that of maize was safe. On the whole, the net transport flux densities of soil Cd in the mining area and control area were -3.05 g·(hm2·a)-1 and -4.05 g·(hm2·a)-1, both of which showed Cd leaching in the soil. However, the points of high atmospheric deposition flux density and exceeding Cd content in rice were mainly distributed around the mining area, which may have posed a potential threat to the health of local residents. Therefore, it is suggested to control the soil Cd pollution through monitoring and planting structure adjustment.

Input Characteristics of Dry Deposition of Atmospheric Particulates and Metals in Farmland in the Suburb of Nanjing

The dry deposition of heavy metals in atmospheric particulates is one of the important sources of heavy metals in agricultural areas, but there are few observational studies on the atmospheric deposition of heavy metals in agricultural areas. In this study, the concentrations of atmospheric particulates with different particle sizes and ten kinds of metal elements in them were analyzed by sampling a typical rice-wheat rotation area in the suburb of Nanjing for one year, and the dry deposition fluxes were estimated using the big leaf model, so as to understand the input characteristics of particulates and heavy metals. The results showed that the particulate concentrations and dry deposition fluxes were high in winter and spring but low in summer and autumn. In winter and spring, coarse particulates (2.1-9.0 μm) and fine particulates (<2.1 μm) had dual effects on particulate pollution, whereas in summer and autumn, particulate pollution was mainly attributed to the fine particulates. The concentrations of metal elements were the lowest in giant particulates (>9.0 μm) and were similar in coarse particulates and fine particulates, whereas Pb, Mn, As, and Cd elements were relatively high in fine particulates. The average annual dry deposition fluxes[g·(m2·a)-1] of particulates was giant particulates (8.31)>coarse particulates (5.99)>fine particulates (0.629). The order of average annual dry deposition fluxes[mg·(m2·a)-1] of the 10 metals was Ca(2096.4)>Al(1710.4)>Zn(855.0)>Fe(256.1)>Pb(40.35)>Cu(31.93)>V(26.21)>Mn(9.10)>As(2.48)>Cd(0.28). The average annual dry deposition fluxes of the 10 metal elements in fine particulates, coarse particulates, and giant particulates were 179.03, 2124.97, and 2724.18 mg·(m2·a)-1, respectively. These results will provide a reference for a more comprehensive understanding of the impact of human activities on the quality and safety of agricultural products and soil ecological environment.

Seasonal variations, source apportionment and dry deposition of chemical species of total suspended particulate in Pengjia Yu Island, East China Sea

Total of 172 total suspended particulate (TSP) samples and its chemical compositions were collected and analyzed from January to December 2010 in Pengjia Yu Island, an open region in East China Sea (ECS). Despite the predominance of sea-salt major ions (Na+, Cl−), the presence of non-sea-salt SO42− (nss-SO42−) and NO3− as well as combustion-derived trace metals clearly establishes the impact of anthropogenic sources over ECS. The annual contributions of coal, heavy-fuel oil and traffic to the measured chemical species were 21.0 %, 15.0 % and 15.5 %, respectively. Especially in spring, the contributions of crustal minerals to measured chemical species during dust period (33.6 %) were higher than that (13.2 %) during non-dust period. The calculated annual average dry deposition fluxes for trace metals and total inorganic nitrogen were 246.1 ± 345.8 μg/m2/d and 2950.4 ± 2245.0 μg/m2/d, suggesting that atmospheric deposition is an important source of nutrient elements for the south of ECS.

Impact of dry deposition flux and dust intrusion phenomena on elemental concentrations of air particulate matter

Depositions of trace elements of air particulates in the atmosphere have gained much attention in recent times due to their environmental, climatic and health impacts. In the current study, trace elements of size-segregated rural and urban particulate matter (PM2.5 and PM2.5−10) were characterized using particle-induced X-ray emission method. Effects of dry deposition flux and Saharan dust intrusion on the elemental concentrations were determined. The mean elemental concentration in the rural fine PM ranged between 0.0002 ± 0.0002 μg m−3 (for Se) and 0.6658 ± 0.5816 μg m−3 (for S) whereas in the urban fine PM the concentration ranged between 0.0007 ± 0.0008 μg m−3 (for As) and 0.5869 ± 0.3429 μg m−3 (for Ca). In the coarse PM fraction, concentration ranged between 0.0001 ± 0.0001 μg m−3 (for Se) and 0.5886 ± 0.5343 μg m−3 (for Ca) at the rural site; and between 0.0002 ± 0.0002 μg m−3 (for Se) and 1.9201 ± 1.911 μg m−3 (for Ca) at the urban site. Mainly crustal elements (Al, Ca, Fe) and ‘pollution’ source element (S) recorded high and significant dry deposition fluxes across the two sites in both PM modes. Deposition flux was relatively higher in the coarse than in the fine PM mode. The average dry deposition flux estimated for fine and coarse PM at the rural and urban sites were 33.68 ± 57.19 μg m−2 day−1 and 47.71 ± 92.19 μg m−2 day−1; 36.66 ± 61.95 μg m−2 day−1 and 107.02 ± 237.71 μg m−2 day−1, respectively. Mainly crustal (Al, Ca, Fe) and “pollution” (S) element recorded high and significant dry deposition fluxes across the two sites and in the two PM modes. The impacts of dust on climate, air quality, and the environment in general have increased the need to better understand the dust flow system. In the current study, dust intruding the study area from the Sahara was analyzed using the NMMB/BSC dust model. The model’s output indicated that, the highest daily surface dust concentration was observed in the central and south-west of Turkey which corresponded with the peak period of Saharan dust transport to the Eastern Mediterranean in the month of March.

Measurements and predictions of ambient air particulates dry depositions at Taichung Shuinan Economic and Trade Park (T.S.E.T.P) during summer and autumn seasons

This study collected ambient air particulate concentrations and dry depositions at Taichung Shuinan Economic and Trade Park (T.S.E.T.P.) sampling site. The global dry depositions model was applied with known particle sizes, pollutant concentrations in ambient air pollutants dry deposition estimates at T.S.E.T.P. site in Central Taiwan. Statistical analysis of the correlated relationships among ambient air particulate concentration, dry depositions, and dry deposition velocities with respect to the meteorological conditions at T.S.E.T.P. site was also conducted. The results indicated that the average dry deposition fluxes were 377.81 µg/m2*min, the average TSP concentrations were 41.53 µg/m3, and the average dry depositions velocity (Vd ) was 15.26 cm/s. In addition, 40 μm was selected as the best ambient air particulate size for the calculated dry deposition velocities to estimate ambient air dry deposition fluxes using the Global model at this T.S.E.T.P. sampling site. Moreover, ambient air particulates concentrations were higher in the fall season than that of the summer season. Sincepollutants parcels were not easily diffused during the fall season because of the low mixed atmospheric layer in this season. Therefore, atmospheric particulates concentrations were higher from the northern side than that of southern side in this study. Furthermore, wind speed V.S. particulate dry depositions and wind V.S. dry depositions velocity displayed a moderate correlated relationship, while particulate dry depositions V.S. particulate dry depositions velocity presented the highest correlated relationship at this T.S.E.T.P. sampling site. However, particulate dry depositions and dry depositions velocity presented significant differences. Finally, particulate dry depositions and dry depositions velocity were not only highly correlation related but also displayed significant differences at the T.S.E.T.P. sampling site.

Applying principal component, health risk assessment, source identification for metallic elements of ambient air total suspended particulates at Taiwan Scientific Park.

This study collected ambient air total suspended particle (TSP) concentrations and dry depositions at Taichung Science Park sampling site. The metallic elements concentrations and dry depositions were analyzed. The possible pollutant sources are discussed in this study. In addition, this study used the principal component analysis method to find metallic element sources and their transportation pathway and distributions at Taichung Science Park (T.S.P). The results indicated that the average highest TSP concentrations and dry deposition fluxes occurred in the autumn and winter seasons. The highest average metallic element concentration and dry deposition was Fe, while the lowest average metallic element concentration and dry deposition was Hg(p). The study results further indicated that the lowest metallic element concentrations and dry depositions all occurred in the summer season. The pollutant parcels originated from the northern Taiwan counties and sea surface in the autumn, winter and spring seasons. Factor 1 was responsible for the local industrial emission results and traffic road dust. The metallic elements Hg(p) yield a value greater than 0.7 in Factor 2 which revealed that ambient air particulate pollutants were generated from Taichung Thermal Power Plant (T.T.P.P.) emissions and were transported from the coastal area of mainland China cities. The mean seasonal concentration differences existed for ambient air particulates, and there were no mean seasonal concentrations differences for all metallic elements. In addition, there were no significant mean concentrations differences for all metallic elements and meteorological factors such as temperature, humidity and wind speed. Therefore, the ambient air metallic element emissions were stable and considered primary emissions sources. The health risk value for metallic element Cr was higher than that for the acceptable health risk value suggested by the EPA. Metallic element Cr revealed that it was no mean seasonal concentrations differences. Thus, metallic element Cr was considered came from local emission source at this T.S.P. sampling site.

Atmospheric Concentration, Particle-bound Content, and Dry Deposition of PCDD/Fs

In this study, the atmospheric total-PCDD/Fs-WHO2005-TEQ concentrations, gas-particle partitioning, PM2.5 concentration, PM2.5-bound total PCDD/Fs-WHO2005-TEQ content and dry deposition flux in Shanghai and Nanjing were investigated from 2018-2020. In Shanghai, the total PCDD/Fs-WHO2005-TEQ concentration dropped from 0.0291 pg-WHO2005-TEQ m–3 from 2018–2019 to 0.0250 pg-WHO2005-TEQ m–3 in 2020, while in Nanjing, it dropped from 0.0423 pg-WHO2005-TEQ m–3 to 0.0338 pg-WHO2005-TEQ m–3. The average concentrations of PCDD/Fs-WHO2005-TEQ in spring and winter in Shanghai and Nanjing were 47.6% and 53.8% higher than those in summer, respectively. From 2018-2019, the average particle phase fractions of total-PCDD/Fs-WHO2005-TEQ in Shanghai and Nanjing were 50.3% and 57.5%, respectively, while in 2020, they were 47.8% and 55.1%, respectively. From 2018-2019, the average PM2.5-bound total PCDD/Fs-WHO2005-TEQ content was 0.342 and 0.493 ng-WHO2005-TEQ g–1 in Shanghai and Nanjing, respectively, while in 2020, it was 0.312 and 0.489 ng-WHO2005-TEQ g–1, respectively. In Shanghai and Nanjing, the average PM2.5-bound total PCDD/Fs-WHO2005-TEQ content in spring and winter was 77.5% and 73.2% higher than that in summer, respectively. From 2018–2019, the dry deposition flux of total-PCDD/Fs-WHO2005-TEQ was 316.3 and 460.5 pg WHO2005-TEQ m–2 month–1 in Shanghai and Nanjing, respectively, while in 2020, it was 272.5 and 368.4 pg WHO2005-TEQ m–2 month–1, respectively. The average dry deposition flux of total-PCDD/Fs-WHO2005-TEQ in spring and winter was 47.6% and 53.8% higher than that summer in Shanghai and Nanjing, respectively. The above results indicate that COVID-19 in 2020 had a positive effect on air quality improvement in PCDD/Fs. On average, more than 98.88% of the total PCDD/Fs-WHO2005-TEQ dry deposition flux was primarily contributed by the particle phase. This was attributed to the fact that dry deposition of particle phase PCDD/Fs was mainly due to gravitational settling accompanied by higher dry deposition velocities, while the gas phase PCDD/Fs were deposited mostly by diffusion at a lower dry deposition velocity. © The Author(s).

Changes in spatial patterns of ammonia dry deposition flux and deposition threshold exceedance according to dispersion model formalism and horizontal resolution.

Ammonia (NH3) emitted into the atmosphere from agricultural sources may affect nearby sensitive ecosystems due to high dry deposition fluxes on vegetation and soil surfaces, contributing to critical load exceedances. Ammonia fluxes near sources are simulated by either short-range atmospheric models or regional models using large grid cell sizes. However, studies are missing on the comparison of the results simulated by these two types of models. This paper presents the effect of model formalism, input factors, especially grid cell size and wind speed and the choice of deposition threshold on the spatial patterns of NH3 dry deposition fluxes and deposition threshold exceedances. We used the Eulerian chemistry-transport model CHIMERE and the Gaussian plume model OPS-ST on two study domains characterised by contrasting land use. We showed that the average annual NH3 dry deposition fluxes over each whole domain are similar for both models. By contrast, NH3 dry deposition fluxes near sources are higher when simulated with OPS-ST that provides analytical solutions that can be sampled with small grid cell sizes (i.e., from 25 to 1600m in this study), than with CHIMERE, which uses large grid cell sizes (i.e., 800 and 1600m). As a result, the spatial patterns of deposition threshold exceedance were very different between both models. These patterns depend mainly on grid cell size, the input factors and the choice of the deposition threshold value. We show that the model formalism has a relatively small effect on the results and that the differences result mainly from the spatial resolutions to which they can be applied. Simulation results must therefore be interpreted carefully, taking into account the simulation conditions.

Seasonal Evolution of Size-Segregated Particulate Mercury in the Atmospheric Aerosol Over Terra Nova Bay, Antarctica.

Size-fractionated particulate mercury (PHg) measurements were performed from November 2017 to January 2018 at Terra Nova Bay (Antarctica) for the first time. Samples were collected every 10 days by a six-stage high-volume cascade impactor with size classes between 10 μm and 0.49 μm. Total PHg concentrations were maxima (87 ± 8 pg m−3) in November, then decreased to values ~40% lower and remained almost constant until the end of the sampling period (~30 pg m−3). The trimodal aerosol mass distribution reveals that from 30% to 90% of the total PHg came in the size > 1.0 μm. Hg in the two coarse fractions was probably produced by the adsorption of oxidized Hg species transported by air masses from the Antarctic plateau or produced locally by sea ice edges. PHg in accumulation mode seemed to be related to gas–particle partitioning with sea salt aerosol. Finally, average dry deposition fluxes of PHg were calculated to be 0.36 ± 0.21 ng m−2 d−1 in the accumulation mode, 47 ± 44 ng m−2 d−1 in the first coarse mode, and 37 ± 31 ng m−2 d−1 in the second coarse mode. The present work contributed to the comprehension of the Hg biogeochemical cycle, but further research studies are needed.

Atmospheric Trace Metal Deposition near the Great Barrier Reef, Australia

Aerosols deposited into the Great Barrier Reef (GBR) contain iron (Fe) and other trace metals, which may act as micronutrients or as toxins to this sensitive marine ecosystem. In this paper, we quantified the atmospheric deposition of Fe and investigated aerosol sources in Mission Beach (Queensland) next to the GBR. Leaching experiments were applied to distinguish pools of Fe with regard to its solubility. The labile Fe concentration in aerosols was 2.3–10.6 ng m−3, which is equivalent to 4.9%–11.4% of total Fe and was linked to combustion and biomass burning processes, while total Fe was dominated by crustal sources. A one-day precipitation event provided more soluble iron than the average dry deposition flux, 0.165 and 0.143 μmol m−2 day−1, respectively. Scanning Electron Microscopy indicated that alumina-silicates were the main carriers of total Fe and samples affected by combustion emissions were accompanied by regular round-shaped carbonaceous particulates. Collected aerosols contained significant amounts of Cd, Co, Cu, Mo, Mn, Pb, V, and Zn, which were mostly (47.5%–96.7%) in the labile form. In this study, we provide the first field data on the atmospheric delivery of Fe and other trace metals to the GBR and propose that this is an important delivery mechanism to this region.

Two years measurement of speciated atmospheric mercury in a typical area of the north coast of China: Sources, temporal variations, and influence of regional and long-range transport

Abstract Measurements of speciated atmospheric mercury (Hg) were conducted at the Changdao Island from October 2013 to July 2015 to characterize their seasonal and diurnal patterns, to identify the relationships between atmospheric Hg and meteorological parameters as well as trace gases, and furthermore to verify the potential sources of atmospheric Hg. There was a seasonal variation of gaseous elemental Hg (GEM) with the order of winter (2.87 ± 1.16 ng m−3), spring (2.58 ± 0.84 ng m−3), summer (2.25 ± 0.51 ng m−3), and fall (2.15 ± 0.39 ng m−3). The mean GEM value (2.52 ± 0.82 ng m−3) in the Changdao Island was about 1.7 times higher than that in the Northern Hemisphere, indicating that the Changdao and peripheral regions were polluted to some extent. Gaseous oxidized Hg (GOM) shows a clear seasonal variation with the highest value in summer (12.2 ± 9.4 pg m−3) and the lowest value in winter (4.6 ± 4.2 pg m−3). Moreover, the mean GOM concentration was significantly higher in daytime (11.9 ± 9.4 pg m−3) than in nighttime (6.3 ± 4.8 pg m−3) mainly due to the influence of solar radiation. In contrast, fine particulate Hg (HgP2.5) exhibited a distinct seasonal trend opposite to that of GOM. There was no significant difference between daytime HgP2.5 concentration (25.6 ± 23.9 pg m−3) and nighttime concentration (30.4 ± 31.2 pg m−3). The size distribution of HgP in PM10 was observed to be one-modal with the peak around the range of 1.1–2.1 μm in the winter, while it was bi-modal with a higher peak in the range of 1.1–2.1 μm and a lower peak in the range of 4.8–5.9 μm in other seasons. Generally, more than half of HgP was concentrated on fine particles (PM2.1). The temporal variation pattern of PM2.5/PM10 ratio was similar to those of HgP2.1/HgP10 or HgP3.3/HgP10. This further supports that HgP is mainly concentrated in fine particles. Correlation analysis shows that the GEM was positively correlated with SO2 and NO2. The average dry deposition flux of HgP10 was calculated to be 4.76 ng m−2 d−1 with a range of 0.86–13.46 ng m−2 d−1 based on all the size-fractionated HgP over the Changdao Island. This indicates that the dry deposition of HgP is an important part of atmospheric Hg deposition in coastal region because it happens all the time.

Atmospheric dry and bulk nitrogen deposition to forest environment in the North China Plain

Atmospheric nitrogen (N) deposition fluxes has dramatically increased in past few decades and has aroused great concerns of its impacts on forest ecosystems. However, complete quantitative information on dry and wet deposition of various reactive nitrogen (Nr) species is very limited for forest environments. Therefore, two-year (2014–2015) measurements of gaseous NH3, NO2, and HNO3 and particulate NH4+ and NO3− (pNH4+ and pNO3-) in air and/or precipitation were conducted in Jigong Mountain National Nature Reserve in the North China Plain (NCP). Our results showed that ambient concentrations of all Nr species were highest in winter and lowest in summer except for NH3; conversely, bulk deposition fluxes of each Nr species generally peaked in summer and were lowest in winter. Annual mean bulk Nr deposition fluxes was 15.5 kg N ha−1 yr−1 (7.9 kg N ha−1 yr−1 for NH4+ and 7.6 kg N ha−1 yr−1 for NO3−), with higher monthly fluxes occurring in spring and summer. Average annual dry Nr deposition fluxes was 44.3 kg N ha−1 yr−1 (30.1 kg N ha−1 yr−1 for reduced N (NH3 plus pNH4+) and 14.2 kg N ha−1 yr−1 for oxidized N (the sum of HNO3, NO2 and pNO3-). Total Nr deposition fluxes (dry plus bulk) reached 59.8 kg N ha−1 yr−1 with more contributions from reduced N than from oxidized N (64% vs 36%). When consider the N critical load (10–20 kg N ha−1 yr−1) in forest ecosystem, potential negative effects may cause by N deposition in the NCP which should be paid more attention.

Comparison of spatial patterns of ammonia concentration and dry deposition flux between a regional Eulerian chemistry-transport model and a local Gaussian plume model

Agricultural activities are the principal sources of ammonia (NH3) emitted into the atmosphere. High ammonia deposition flux may impact sensitive ecosystems. Regional models of NH3 dispersion, transport and deposition may under- or overestimate NH3 fluxes. We compared NH3 dry deposition fluxes simulated with local and regional models on different theoretical scenarios characterised by varying the values of several input factors: grid cell sizes, characteristics of the NH3 sources such as location and emission rate, characteristics such as canopy resistance (Rc) or roughness length (z0) at the NH3 sinks, and meteorological conditions such as wind speed and direction. Our results showed that, for a given grid cell size, both models provide similar predictions of average NH3 concentration and dry deposition flux over the whole simulation domain. A sensitivity analysis of NH3 concentration and dry deposition flux to wind speed and to surface resistance also showed a similar behaviour between both models. However, the differences of model formalism and changes in the values of the input factors, especially grid cell size and vertical resolution, provide different spatial patterns of NH3 dry deposition flux and concentration. Our results would suggest that regional models operating with large grid cell sizes (e.g. larger than 1 km) could not predict accurately patterns of NH3 dry deposition fluxes close to the sources (e.g. a few tens or hundreds of metres) on heterogeneous landscapes in terms of NH3 fluxes.

Sources and dry deposition of carbonaceous aerosols over the coastal East China Sea: Implications for anthropogenic pollutant pathways and deposition

75 paired TSP and PM2.5 samples were collected over four seasons on Huaniao Island (HNI), an island that lies downwind of continental pollutants emitted from mainland China to the East China Sea (ECS). These samples were analyzed for organic carbon (OC) and elemental carbon (EC), with a special focus on char-EC (char) and soot-EC (soot), to understand their sources, and the scale and extent of pollution and dry deposition over the coastal ECS. The results showed that char concentrations in PM2.5 and TSP averaged from 0.13 to 1.01 and 0.31–1.44 μg m−3; while for soot, they were from 0.03 to 0.21 and 0.16–0.56 μg m−3, respectively. 69.0% of the char and 36.4% of the soot were present in PM2.5. The char showed apparent seasonal variations, with highest concentrations in winter and lowest in summer; while soot displayed maximum concentrations in fall and minimum in summer. The char/soot ratios in PM2.5 averaged from 3.29 to 17.22; while for TSP, they were from 1.20 to 7.07. Both of the ratios in PM2.5 and TSP were highest in winter and lowest in fall. Comparisons of seasonal variations in OC/EC and char/soot ratios confirmed that char/soot may be a more effective indicator of carbonaceous aerosol source identification than OC/EC. Annual average atmospheric dry deposition fluxes of OC and EC into ECS were estimated to be 229 and 107 μg m−2 d−1, respectively, and their deposition fluxes significantly increased during episodes. It was estimated that the loadings of OC + EC and EC accounted for 1.3% and 4.1% of the total organic carbon and EC in ECS surface sediments, respectively, implying a relatively small contribution of OC and EC dry deposition to organic carbon burial. This finding also indicates a possibly more important contribution of wet deposition to organic carbon burial in sediments of ECS, and this factor should be considered for future study.

Atmospheric deposition of antimony in a typical mercury-antimony mining area, Shaanxi Province, Southwest China

Mercury-antimony (HgSb) mining activities are important anthropogenic sources of Hg and Sb to the local environment. The Xunyang HgSb mine situated in Shaanxi Province is an active Hg mine in China. To understand the emission, transportation, and deposition of Sb through HgSb mining activities, current study systematically monitored the Sb concentration in precipitation in the Xunyang HgSb mining district. Five groups of experimental pots were carefully designed to further investigate the influence of HgSb mining activities on the Sb contamination in the local surface soil. Based on the overtime increasing of the Sb concentrations in soil from experimental pots, for the first trial, we estimated the atmospheric deposition flux/mass of Sb in the Xunyang HgSb mining district. Our results showed that the concentrations of Sb in precipitation in the Xunyang HgSb mining district ranged from 0.71 μg L−1 to 19 μg L−1 (mean = 4.2 ± 4.5 μg L−1), which was orders of magnitude higher than that at the control site. As expected, the concentration of Sb in precipitation was highly elevated near of the HgSb smelter and gradually decreased with distance from the smelter. After 12 months exposure, Sb concentrations in soil of experimental pots were increased by 1.2–8.5 times. The average atmospheric wet and dry deposition flux of Sb in the Xunyang HgSb mining district were 7.2 ± 6.9 μg m−2 day−1 and 2.1 ± 4.7 mg m−2 day−1, respectively; the annual wet and dry deposition mass of Sb through HgSb mining activities were estimated to be 1.6 t y−1 and 158 t y−1, respectively, indicating that dry deposition was the dominant pathway (98 ± 1.2%) for the removal of Sb from the atmosphere. Our results confirmed that the ongoing HgSb mining activities resulted to serious Sb contamination to terrestrial ecosystems, posing a potential threat to local residents in the Xunyang HgSb mining district.

Seasonal atmospheric deposition and air–sea gas exchange of polycyclic aromatic hydrocarbons over the Yangtze River Estuary, East China Sea: Implications for source–sink processes

In this work, air samples and surface seawater samples covering four seasons from March 2014 to January 2015 were collected from a background receptor site in the YRE to explore the seasonal fluxes of air–sea gas exchange and dry and wet deposition of 15 polycyclic aromatic hydrocarbons (PAHs) and their source–sink processes at the air–sea interface. The average dry and wet deposition fluxes of 15 PAHs were estimated as 879 ± 1393 ng m−2 d−1 and 755 ± 545 ng m−2 d−1, respectively. Gaseous PAH release from seawater to the atmosphere averaged 3114 ± 1999 ng m−2 d−1 in a year round. The air–sea gas exchange of PAHs was the dominant process at the air–sea interface in the YRE as the magnitude of volatilization flux of PAHs exceeded that of total dry and wet deposition. The gas PAH exchange flux was dominated by three-ring PAHs, with the highest value in summer and lowest in winter, indicating a marked seasonal variation owing to differences in Henry's law constants associated with temperature, as well as wind speed and gaseous-dissolved gradient among seasons. Based on the simplified mass balance estimation, a net 11 tons y−1 of PAHs (mainly three-ring PAHs) were volatilized from seawater to the atmosphere in a ∼20,000 km2 area in the YRE. Other than the year-round Yangtze River input and ocean ship emissions, the selective release of low-molecular-weight PAHs from bottom sediments in winter due to resuspension triggered by the East Asian winter monsoon is another potential source of PAHs. This work suggests that the source–sink processes of PAHs at the air–sea interface in the YRE play a crucial role in regional cycling of PAHs.

The concentration, source and deposition flux of ammonium and nitrate in atmospheric particles during dust events at a coastal site in northern China

Abstract. Asian dust has been reported to carry anthropogenic reactive nitrogen during transport from source areas to the oceans. In this study, we attempted to characterize NH4+ and NO3− in atmospheric particles collected at a coastal site in northern China during spring dust events from 2008 to 2011. Based on the mass concentrations of NH4+ and NO3− in each total suspended particle (TSP) sample, the samples can be classified into increasing or decreasing types. In Category 1, the concentrations of NH4+ and NO3− were 20–440 % higher in dust day samples relative to samples collected immediately before or after a dust event. These concentrations decreased by 10–75 % in the dust day samples in Categories 2 and 3. Back trajectory analysis suggested that multiple factors, such as the transport distance prior to the reception site, the mixing layer depth on the transport route and the residence time across highly polluted regions, might affect the concentrations of NH4+ and NO3−. NH4+ in the dust day samples was likely either in the form of ammonium salts existing separately to dust aerosols or as the residual of incomplete reactions between ammonium salts and carbonate salts. NO3− in the dust day samples was attributed to various formation processes during the long-range transport. The positive matrix factorization (PMF) receptor model results showed that the contribution of soil dust increased from 23 to 36 % on dust days, with decreasing contributions from local anthropogenic inputs and associated secondary aerosols. The estimated deposition flux of NNH4++NO3− varied greatly from event to event; e.g., the dry deposition flux of NNH4++NO3− increased by 9–285 % in Category 1 but decreased by 46–73 % in Category 2. In Category 3, the average dry deposition fluxes of particulate nitrate and ammonium decreased by 46 % and increased by 10 %, respectively, leading to 11–48 % decrease in the fluxes of NNH4++NO3−.

Sensitivity Analyses for Atmospheric Scavenging Ratio of Total PCDD/Fs-TEQ Wet Deposition: Case of Wuhu City, China

This study investigated the monthly average dry, wet and total deposition fluxes in total-PCDD/Fs-WHO2005-TEQ in Wuhu and Bengbu, respectively. In addition, sensitivity analyses for both scavenging ratio and wet deposition of total-PCDD/Fs-WHO2005-TEQ in Wuhu were also conducted. In 2015, the annual dry deposition fluxes, wet deposition fluxes, and total deposition fluxes were 6407, 1538, and 7945 pg WHO2005-TEQ m–2 year–1 in Wuhu, and were 7101, 1525, and 8626 pg WHO2005-TEQ m–2 year–1 in Bengbu. The annual scavenging ratios of total-PCDD/Fs-WHO2005-TEQ were 30144 and 31267 in Wuhu and Bengbu, respectively. As to the sensitivity analysis for the scavenging ratio of total-PCDD/Fs-WHO2005-TEQ, the most positive sensitivity parameters were PCDD/Fs concentration and PM10 concentration; the second positively correlated sensitivity parameter was PM2.5 concentration, then, followed by atmospheric temperature, which was negatively correlated; the last negative correlated sensitivity factor was the rainfall. In terms of the sensitivity analysis for wet deposition of total-PCDD/Fs-WHO2005-TEQ, the most positive sensitivity parameter was air temperature; the second positive or negative correlated sensitivity factor was atmospheric PCDD/Fs mass concentration, followed by PM2.5 and PM10 concentration, which were positively correlated; the last positive correlated sensitivity factor was the rainfall. This study led to greater insight into the parameters affecting the atmospheric wet deposition of PCDD/Fs, which will benefit development of appropriate control strategies for PCDD/Fs and provided useful information for the scientific community.

Sensitivity Analysis of Atmospheric PM2.5-Bound Content and Dry Deposition of Total PCDD/Fs-TEQ: In the Case of Xiamen and Zhangzhou, China

This study investigated atmospheric PM2.5 concentration, PM2.5/PM10 ratio, total PCDD/Fs concentration, PCDD/F phase distribution, PM2.5-bound total PCDD/Fs-WHO2005-TEQ content, and dry deposition of PCDD/Fs for Xiamen and Zhangzhou Cities during 2015–2017, and sensitivity analysis of both atmospheric PM2.5-bound total PCDD/Fs-WHO2005-TEQ content and dry deposition of PCDD/Fs in these two cities. During 2015–2017, the three-year average concentration of PM2.5 in Xiamen was 27.6 µg m–3, while that of Zhangzhou was 33.9 µg m–3; this level is still higher than the WHO annual PM2.5 standard (10.0 µg m–3). In addition, the summer PM2.5-bound total PCDD/Fs-WHO2005-TEQ content in Xiamen and Zhangzhou Cities was 0.131 ng-WHO2005-TEQ g–1 and 0.161 ng-WHO2005-TEQ g–1. And it is lower than the average of the other three seasons. In Xiamen, the average monthly dry deposition flux in these three years was 322 pg WHO2005-TEQ m–2 month–1, while that of Zhangzhou was 378 pg WHO2005-TEQ m–2 month–1, respectively. Sensitivity analysis of atmospheric PM2.5-bound total PCDD/Fs-WHO2005-TEQ content showed that the most sensitive parameters are total PCDD/F mass concentration and PM10 concentration, followed by atmospheric temperature and PM2.5 concentration; in addition, the sensitivity analysis of atmospheric dry deposition is similar to those of atmospheric PM2.5-bound total PCDD/Fs-WHO2005-TEQ content. The results of this study provide useful information for better understanding PM2.5, particle-bound PCDD/Fs content and PCDD/Fs dry deposition in the ambient air of urban cities.